Poly Trimethylene Terephthalate. Based Blends, IPNs, Composites and Nanocomposites 9789811973024, 9789811973031

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Materials Horizons: From Nature to Nanomaterials

A. R. Ajitha Sabu Thomas Editors

Poly Trimethylene Terephthalate Based Blends, IPNs, Composites and Nanocomposites

Materials Horizons: From Nature to Nanomaterials Series Editor Vijay Kumar Thakur, School of Aerospace, Transport and Manufacturing, Cranfield University, Cranfield, UK

Materials are an indispensable part of human civilization since the inception of life on earth. With the passage of time, innumerable new materials have been explored as well as developed and the search for new innovative materials continues briskly. Keeping in mind the immense perspectives of various classes of materials, this series aims at providing a comprehensive collection of works across the breadth of materials research at cutting-edge interface of materials science with physics, chemistry, biology and engineering. This series covers a galaxy of materials ranging from natural materials to nanomaterials. Some of the topics include but not limited to: biological materials, biomimetic materials, ceramics, composites, coatings, functional materials, glasses, inorganic materials, inorganic-organic hybrids, metals, membranes, magnetic materials, manufacturing of materials, nanomaterials, organic materials and pigments to name a few. The series provides most timely and comprehensive information on advanced synthesis, processing, characterization, manufacturing and applications in a broad range of interdisciplinary fields in science, engineering and technology. This series accepts both authored and edited works, including textbooks, monographs, reference works, and professional books. The books in this series will provide a deep insight into the state-of-art of Materials Horizons and serve students, academic, government and industrial scientists involved in all aspects of materials research. Review Process The proposal for each volume is reviewed by the following: 1. Responsible (in-house) editor 2. One external subject expert 3. One of the editorial board members. The chapters in each volume are individually reviewed single blind by expert reviewers and the volume editor.

A. R. Ajitha · Sabu Thomas Editors

Poly Trimethylene Terephthalate Based Blends, IPNs, Composites and Nanocomposites

Editors A. R. Ajitha International and Interuniversity Centre for Nanoscience and Nanotechnology Mahatma Gandhi University Kottayam, India

Sabu Thomas School of Chemical Science, International and Interuniversity Centre for Nanoscience and Nanotechnology Mahatma Gandhi University Kottayam, India

ISSN 2524-5384 ISSN 2524-5392 (electronic) Materials Horizons: From Nature to Nanomaterials ISBN 978-981-19-7302-4 ISBN 978-981-19-7303-1 (eBook) https://doi.org/10.1007/978-981-19-7303-1 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Contents

Part I 1

Introduction

Poly(Trimethylene Terephthalate): Introduction . . . . . . . . . . . . . . . . . A. R. Ajitha, V. K. Abitha, and Sabu Thomas

Part II

PTT Based Blends and IPNs

2

PTT-Based Polymer Blends and IPNs: Preparation Methods . . . . . . Sreekala S. Sharma, V. N. Anjana, and Anu K. John

3

Characterization Techniques of PTT-Based Polymer Blends and IPNs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V. R. Remya and H. Akhina

4

3

PTT/Rubber, Thermoplastic and Thermosetting Polymer Blends and IPNs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rinku Mariam Thomas, Sreedha Sambhudevan, S. Hema, and Arunima Reghunadhan

13

37

49

Part III PTT Based Composites and Nanocomposites 5

PTT-Based Micro and Nanocomposites: Methods of Preparation and Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Anju Paul and Sreedevi Krishnakumar

81

6

Characterization Techniques Used to Study Various Macro and Nanocomposites of PTT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 P. S. Sari and Arunima Reghunadhan

7

Crystallization and Solid-State Characterization of Poly(Trimethylene Terephthalate) and Its Nanocomposites . . . . . . 129 Nadarajah Vasanthan

v

vi

Contents

8

Functional Properties of PTT-Based Composites and Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Sandra Paszkiewicz

9

PTT-Based Green Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 Amit Chanda, Jaideep Adhikari, Manojit Ghosh, and Prosenjit Saha

10 Morphological Studies and Its Effects on PTT-Based Micro, Nanocomposites, and Polymer Blends Properties . . . . . . . . . . . . . . . . . 187 Natália Ferreira Braga, Erick Gabriel Ribeiro dos Anjos, Thais Ferreira da Silva, Larissa Stieven Montagna, and Fabio Roberto Passador Part IV Applications of PTT 11 Industrial Applications of PTT-Based Polymer Blends, Composites, and Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 S. Hema, Sreedha Sambhudevan, C. Sreelekshmi, Malavika Sajith, and K. Rashid Sulthan 12 Textile Applications of PTT-Based Polymer Blends, Composites, and Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 Abjesh Prasad Rath and M. K. Kanny 13 Antistatic Packaging for Electronic Devices of PTT-Based Polymer Blends, Composites, and Nanocomposites . . . . . . . . . . . . . . . 251 Natália Ferreira Braga, Thais Ferreira da Silva, Erick Gabriel Ribeiro dos Anjos, Henrique Morales Zaggo, Yves Nicolau Wearn, Eduardo Antonelli, and Fabio Roberto Passador 14 Comparative Study of Physical, Chemical, and Dyeing Performances of PET, PTT, and PET/PTT Bicomponent Filaments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 Marwa Souissi, Ramzi Khiari, and Nizar Meksi

About the Editors

A. R. Ajitha completed her Ph.D. in Polymer Science and currently working as assistant professor at MES College Marampally, Kerala. She received a patent for an invention entitled “A Poly (Trimethylene Terephthalate)/polypropylene blend nanocomposites- for effective electromagnetic shielding material for electronic applications” in 2021. Dr. Ajitha has over 6 years of experience in this field, and her research areas include the preparation of nanocomposites, their characterization, and modification of nanofillers. Dr. Ajitha has published eight research articles in international journals and edited one book and ten book chapters. Sabu Thomas is currently a vice chancellor of Mahatma Gandhi University. He is also a full professor of Polymer Science and Engineering at the School of Chemical Sciences of Mahatma Gandhi University, Kottayam, Kerala, India, and the founder director and the professor of the International and Inter-University Centre for Nanoscience and Nanotechnology. Dr. Thomas’s ground-breaking inventions in polymer nanocomposites, polymer blends, green bionanotechnological, and nanobiomedical sciences have made transformative differences in the development of new materials for automotive, space, housing, and biomedical fields. In collaboration with India’s premier tyre company, Apollo Tyres, Professor Thomas’s group invented new high-performance barrier rubber nanocomposite membranes for inner tubes and inner liners for tyres. Prof Thomas has published over 1000 peer-reviewed research papers, reviews, and book chapters. He has co-edited and written 137 books published by Royal Society, Wiley, Wood head, Elsevier, CRC Press, Springer, Nova, etc. He is the inventor of 15 patents. Prof Thomas has guided nearly 107 Ph.D. scholars in India and abroad. Prof Thomas is an outstanding leader with sustained international acclaim for his work in nanoscience, polymer science and engineering, polymer nanocomposites, elastomers, polymer blends, interpenetrating polymer networks, polymer membranes, green composites and nanocomposites, nanomedicine, and green nanotechnology.

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Part I

Introduction

Chapter 1

Poly(Trimethylene Terephthalate): Introduction A. R. Ajitha, V. K. Abitha, and Sabu Thomas

1 Introduction 1.1 Poly(Trimethylene Terephthalate) (PTT) Poly(trimethylene terephthalate (PTT) is an important semicrystalline linear aromatic polyester with three methylene units in its chemical structure. The physical and chemical properties of PTT are based on the odd number of methylene groups. The structure of PTT is given in Fig. 1, and this distinct structure of PTT leads to tremendous elastic recovery capability. They are widely used in many areas such as fibers, films, and engineering thermoplastics. It can be considered as a promising engineering plastic and textile fiber, since PTT is an excellent fiber material and exhibits excellent fiber performance than nylons and other polyesters. The crystalline structure of PTT shows that the aliphatic part of PTT has the gauche–gauche conformation and has a triclinic crystalline structure [1]. PTT is derived commercially from terephthalic acid and 1,3-propanediol (PDO) and carried out at a high temperature, pressure, and vacuum. Poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) were developed and commercially produced for more than 60 years. Even though Polytrimethlyene terephthalate A. R. Ajitha (B) Department of Chemistry, MES College Marampally, Aluva, Kerala, India e-mail: [email protected] A. R. Ajitha · S. Thomas International and Interuniversity Centre for Nanoscience and Nanotechnology, Kottayam, Kerala, India V. K. Abitha · S. Thomas School of Chemical Sciences, Mahatma Gandhi University, Kottayam, Kerala, India S. Thomas School of Energy Materials, Mahatma Gandhi University, Kottayam, Kerala, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. R. Ajitha and S. Thomas (eds.), Poly Trimethylene Terephthalate, Materials Horizons: From Nature to Nanomaterials, https://doi.org/10.1007/978-981-19-7303-1_1

3

4 Fig. 1 Chemical structure of PTT

A. R. Ajitha et al. O

O

O

O

n

(PTT) was also reported several years ago and patented in 1941; it was not commercialized until the late 1990s. PTT was first reported by Whinfield and Dickson, but it was later commercially synthesized by Shell Chemicals after the development of 1,3propanediol in a very low-cost method. Shell Chemicals developed 1,3 –propanediol (PDO) monomer by hydroformylation of ethylene oxide [2]. PTT was first synthesized through the polycondensation process of the terephthalic acid and 1,3- propanediol in 1941 [3]. PTT has been commercially prepared by Shell Chemicals under the trade name Cortera. PET has two methylene units between terephthalate units, and it can be termed as 2 GT. PBT is also termed 4GT due to its four methylene units present between terephthalate units. Similarly, PTT is termed as 3 GT since it has three methylene units between the terephthalate units [4]. On comparing with PET and PBT, it can be clearly said that PTT has prominent or similar physical properties to PET and its processing characteristics similar to PBT. The excellent stain resistance, dyeing ability, and softness make them as a good candidate for fiber applications. Due to these properties, PTT has more applicability of PTT in carpet and other textile applications is interesting more than other polyesters [5]. PTT exhibits properties between those of PET and PBT with comparable important properties of PET and processing characteristics of PBT. This makes PTT as good material in many fields, such as fiber, film, carpets, clothing materials, and engineering thermoplastic applications. The PTT has better elastic property than PET and PBT [6]. Qualitative differential scanning calorimetry (DSC) reported that the melting temperature of PTT has been suggested to be about 237 °C and a glass transition temperature between 42–72 °C [7]. As we already discussed in comparison with poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), PTT has mechanical properties similar to PET and has similar processing characteristics of PBT. This is favored to be a potential candidate in carpet and other textile fiber applications because of its stain resistance, softness, etc. However, its applications as an engineering plastic are limited due to its low heat distortion temperature, low melt viscosity, and pronounced brittleness [8–11]. And, it can be overcome by blending/incorporating with other polymers or nanofillers. Numerous studies based on crystallization, electrical, mechanical, and various properties of PTT have been reported [12–22].

1 Poly(Trimethylene Terephthalate): Introduction

5

2 Manufacturing of PTT As we already discussed, the synthesis of 1, 3-propanediol (PDO) in a much more cost-effective method by Shell Chemicals opened the door to the relatively inexpensive synthesis of PTT. Shell Chemicals synthesized PDO by hydroformylation of ethylene oxide with synthesis gas. The route introduced by Shell Chemicals is tremendously attractive. Then, the commonly used method for the inexpensive synthesis of PTT was by the direct esterification and polycondensation with terephthalic acid and PDO as explained by Whinfield and Dickson. The esterification reaction is carried out in temperature control of 215–235 °C and a pressure of 0.2–0.3 MPa. A temperature range of 250–270 °C is maintained for polycondensation reaction under vacuum [23].

3 Properties and Applications of PTT Poly(trimethylene terephthalate) (PTT) is a relatively new material that has recently come to market. PTT spinning processes have been developed for carpet, textile, and nonwoven fibers, as well as special applications such as racket guts and musical bowstrings, papermaking machine fabrics, umbrella fabric, pantyhose, cheese packaging, artificial leather, and hook-and-loop fasteners. PTT can be molded into magnetic recording disks, bottles, and electric connectors, as well as processed into a film for packaging. PTT’s recent commercialization is due to a variety of factors, including new and more cost-effective polymerization processes, as well as an intriguing and valuable combination of characteristics. Physical, mechanical, rheological, chemical resistance, flammability, and toxicity characteristics of PTT are listed in Tables 1, 2, 3, 4, and Fig. 2 [24–26].

4 Summary PTT is an important aromatic semicrystalline polyester. Understanding the full properties and basic concepts of PTT may increase their usage in the future applications. The present chapter discusses some general details of PTT. The following chapters will provide a detailed discussion on PTT-based blends, interpenetrating networks, and composites. Its preparations, properties, and application are the main focused areas.

6 Table 1 Physical properties of PTT

A. R. Ajitha et al. Physical properties Density (@20)

1.33–1.35, 1.432(C)–1.295(A)

Color

White

Refractive index

1.6–1.62, 1.636 (Uniaxial Orientation)

Birefringence

0.029–0.06

Melting temp

226–233 (°C)

Decomposition temp

265,374 (°C)

Thermal expansion coefficient 0.25–1.325 × 10–4

Table 2 Mechanical and rheological properties of PTT

Glass transition temperature

40–75 (40DSC) 55(DMA) (°C)

Heat of fusion

60.3–145.63 (Jg−1 )

Enthalpy of melting (hard segments)

43.2 (Jg−1 )

Mechanical and Rheological properties Tensile strength

50–65; 110–165 MPa (15–30% glass fiber (gf))

Tensile modulus

2,400–2,550; 6,200–11,000 (15–30% gf)

Yield stress

60 MPa

Elongation

10–15; 2.0–3% (15–30% gf); 36–42% (fiber)

Yield strain

5.5–6%

Flexural strength

84–103; 170–245 (15–30% gf) (MPa)

Flexural modulus

2,400–2,800; 5700–9600 MPa (15–30% gf)

Impact strength

25–50 KJm−2 (15–30% gf) Charpy (Un) (23 °C)

Impact strength

30–45 KJm−2 (15–30% gf) Charpy (Un) (−30 °C)

Impact strength

4–5; 5–9 KJm−2 (15–30% gf) Charpy (n) (23 °C)

Impact strength

6–9 KJm−2 (15–30% gf) Charpy (n) (−30 °C)

Impact strength

214 Jm−1 Izod (Un) (23 °C)

Impact strength

27–57 Jm−1 Izod (Un) (23 °C) (continued)

1 Poly(Trimethylene Terephthalate): Introduction Table 2 (continued)

7

Mechanical and Rheological properties Tenacity

3.4–3.7 Cn/dtex

Poisson ratio

0.35 (15–30% glass fiber)

Shrinkage

1–1.3; 0.3–0.8 (15–30% glass fiber)

Intrinsic viscosity

0.56–0.94dlg−1 (25 °C)

Melt viscosity

85 Pa S

Melt index

35 g/10 min (250 °C/2.16 kg)

Water absorption

0.2–0.4% (equilibrium in water at 23 °C)

Table 3 Chemical resistance of PTT Chemical Resistance Alcohols

Very good

Aliphatic hydrocarbons

Very good

Aromatic hydrocarbons

Very good

Esters

Good

Greases & Oils

Very good

Halogenated hydrocarbons

Poor

Good solvent

Tetrachloroethane/phenol, hexafl uoroisopropanol, trifl uoroacetic acid/methylene chloride

Table 4 Flammability and toxicity of PTT Flammability and Toxicity Autoignition temperature

> 300 °C

Activitation energy of thermal decomposition

192–210 °C

Volatile products of combustion

Acrolein, Allyl alcohol, CO, CO2 , Ethanol, Methanol, Acetic acid

NFPA: Health, Flammability, Reactivity rating

0/1/0

Carcinogenic effect

Not listed by ACGIH, NIOSH, NTP

OSHA

5 (respirable), 15 (total)mg/m3

Oral rat, LD50

> 5,000 mg/kg

8

A. R. Ajitha et al.

Fig. 2 Commercial applications of PTT

References 1. Chandran S, Antolasic F, Eichhorn K, Shanks RA, Thomas S (2014) Stereochemistry and miscibility of epoxy resin–poly (trimethylene terephthalate) blends. RSC Adv 4:25420–25429 2. Kelsey DR, Kiibler KS, Tutunjian PN (2005) Thermal stability of poly (trimethylene terephthalate). Polymer 46:8937–8946 3. Kotek R (2008) Recent advances in polymer fibers. Polym Rev 48:221–229 4. Kim K, Bae J, Kim Y (2001) Infrared spectroscopic analysis of poly (trimethylene terephthalate). Polymer 42:1023–1033 5. Chen J, Wei W, Qian Q, Xiao L, Liu X, Xu J, Huang B, Chen Q (2014) The structure and properties of long-chain branching poly (trimethylene terephthalate). Rheol Acta 53:67–74 6. Zeng W, Li H, Liu T, Yan S (2008) A study on the double melting behavior of poly (trimethylene terephthalate). Chin Sci Bull 53:2145–2155 7. Pyda M, Boller A, Grebowicz J, Chuah H, Lebedev B, Wunderlich B (1998) Heat capacity of poly (trimethylene terephthalate). J Polym Sci, Part B: Polym Phys 36:2499–2511 8. Aravind I, Albert P, Ranganathaiah C, Kurian J, Thomas S (2004) Compatibilizing effect of EPM-g-MA in EPDM/poly(trimethylene terephthalate) incompatible blends. Polymer 45:4925–4937

1 Poly(Trimethylene Terephthalate): Introduction

9

9. Ho R-M, Ke K-Z, Chen M (2000) Crystal structure and banded spherulite of poly (trimethylene terephthalate). Macromolecules 33:7529–7537 10. Chuah HH (2001) Orientation and structure development in poly (trimethylene terephthalate) tensile drawing. Macromolecules 34:6985–6993 11. Wang B, Li CY, Hanzlicek J, Cheng SZ, Geil PH, Grebowicz J, Ho R-M (2001) Poly(trimethylene terephthalate) crystal structure and morphology in different length scales. Polymer 42:7171–7180 12. Tsou C-Y, Wu C-L, Tseng Y-C, Chiu S-H, Suen M-C, Hung W, Tsou C-H (2017) Isothermal crystallization kinetics effect on the tensile properties of PLA/PTT polymer composites. Strength Mater 49:171–179 13. Huang C-L, Wang Y-J, Fan Y-C, Hung C-L, Liu Y-C (2017) The effect of geometric factor of carbon nanofillers on the electrical conductivity and electromagnetic interference shielding properties of poly(trimethylene terephthalate) composites: a comparative study. J Mater Sci 52:2560–2580 14. Paszkiewicz S, Szymczyk A, Kasprowiak I, Zenker M, Pilawka R, Linares A, Ezquerra T, Rosłaniec Z (2017) Electrical and rheological characterization of poly (trimethylene terephthalate) hybrid nanocomposites filled with COOH functionalized MWCNT and graphene nanosheets, Polymer Composites 15. Gupta A, Choudhary V (2011) Electromagnetic interference shielding behavior of poly(trimethylene terephthalate)/multi-walled carbon nanotube composites. Compos Sci Technol 71:1563–1568 16. Huang CL, Xu WZ, Wu SH, Chen WC, Lin JH (2015) Effect of oxidation condition on the synthesis of graphene nanosheets and the electrical properties of poly(trimethylene terephthalate) composites prepared using these nanosheets, applied mechanics & materials, 749 17. Huang CL, Wang YJ, Fan YC (2016) Morphological features and crystallization behavior of the conductive composites of poly (trimethylene terephthalate)/graphene nanosheets, J Appl Polym Sci, 133 18. Smith L, Vasanthan N (2015) Effect of clay on melt crystallization, crystallization kinetics and spherulitic morphology of poly(trimethylene terephthalate) nanocomposites. Thermochim Acta 617:152–162 19. Lugito G, Woo EM (2016) Three types of banded structures in highly birefringent poly(trimethylene terephthalate) spherulites. J Polym Sci, Part B: Polym Phys 54:1207–1216 20. Ramachandran AA, Mathew LP, Thomas S (2019) Effect of MA-g-PP compatibilizer on morphology and electrical properties of MWCNT based blend nanocomposites: New strategy to enhance the dispersion of MWCNTs in immiscible poly(trimethylene terephthalate)/polypropylene blends. Eur Polymer J 118:595–605 21. Mathew L, Saha P, Kalarikkal N, Thomas S, Strankowski M (2018) Tuning of microstructure in engineered poly (trimethylene terephthalate) based blends with nano inclusion as multifunctional additive. Polym Testing 68:395–404 22. Mathew LP, Kalarikkal N, Thomas S, Volova T (2018) An effective EMI shielding material based on poly(trimethylene terephthalate) blend nanocomposites with multiwalled carbon nanotubes. New J Chem 42:13915–13926 23. Schultz J, Wu J (2002) Poly(Trimethylene Terephthalate)—A Newly Commercialized Member of the Polyester Family: Sections 1–4, handbook of thermoplastic polyesters: homopolymers, copolymers, blends, and composites, 551–562. 24. Fakirov S (2002) Handbook of thermoplastic polyesters, Wiley-Vch 25. Wypych G (2016) Handbook of polymers, Elsevier 26. Chan CH, Chia CH, Thomas S (2014) Physical chemistry of macromolecules: macro to nanoscales, CRC Press

Part II

PTT Based Blends and IPNs

Chapter 2

PTT-Based Polymer Blends and IPNs: Preparation Methods Sreekala S. Sharma, V. N. Anjana, and Anu K. John

1 Introduction Poly(trimethylene terephthalate) (poly-1,3-propylene terephthalate, PTT) is one type of commercial polyester. It is a semi-aromatic and semicrystalline thermoplastic that can be easily moulded, thermoformed, and spun into fibres. PTT is the copolymer of 1,3-propanediol (PDO) and terephthalic acid or dimethyl terephthalate (Fig. 1). It is synthesized and patented in 1941 (Whinfield and Dickson) [1]. However, due to the non-availability of 1,3-propanediol in sufficient quantity and purity, the synthesis was not commercialized at that time. Then, an alternative method was developed by Shell to produce PDO economically which is the hydroformylation of ethylene oxide. This leads to the commercialization of PTT. The mechanical and thermophysical properties of PTT are similar to polyethylene terephthalate (PET) while its moulding properties are analogous to poly(butylene terephthalate (PBT). PTT has good tensile and flexural strength, good dimensional stability, and excellent flow and surface finish like PET. It also has good chemical resistance to a broad range of chemicals, including gasoline, carbon tetrachloride, oils, fat, alcohols, glycols, diluted acids, and bases similar to PBT. However, it is affected by hot water and steam [2].

S. S. Sharma (B) · V. N. Anjana Sree Sankara Vidyapeetom College, Valayanchirangara, Perumbavoor 683556, India e-mail: [email protected] A. K. John Bharata Mata College, Thrikkakara 682021, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. R. Ajitha and S. Thomas (eds.), Poly Trimethylene Terephthalate, Materials Horizons: From Nature to Nanomaterials, https://doi.org/10.1007/978-981-19-7303-1_2

13

14

S. S. Sharma et al.

Fig. 1 Poly(trimethylene terephthalate) molecule

2 Synthesis of Poly(Trimethylene Terephthalate) (PTT) It is produced by methods such as esterification or transesterification. In an esterification reaction, PDO is treated with purified terephthalic acid (PTA) and in a transesterification reaction, PDO is treated with dimethyl terephthalate (DM). The synthesis methodology is similar to that of PET. Highly active catalysts like titanium and tin are used for the polymerization reaction due to the low reactivity of PDO. PTT is polymerized at the temperature range of 250–275 °C. Acrolein and allyl alcohol are the volatile by-products of PTT production. The reaction schemes for the synthesis of PTT are given in Figs. 2 and 3. Because of the higher melt degradation rate and a faster crystallization rate, PTT requires special consideration in polymerization, pelletizing, and solid-state treatment. Direct esterification of PDO with TPA is a more cost-effective route than transesterification with DMT [3].

Fig. 2 Synthesis of PTT by esterification reaction [4]

2 PTT-Based Polymer Blends and IPNs: Preparation Methods

15

Fig. 3 Synthesis of PTT by transesterification reaction [4]

3 Properties of Poly(Trimethylene Terephthalate) (PTT) Three methylene units are present in the glycol moiety of PTT and are hence called odd number polyester. It crystallizes rapidly and is thus difficult to dissolve in various solvents, unlike PET. It has a heat of fusion between 28 and 30 kJ/mol and an equilibrium melting temperature of about 510 K (237 °C) [5]. Important properties of pristine PTT are given in Table 1. PTT is an opaque thermoplastic in the solid state, but in the liquid state, it can be extruded into sheets and films. The unique conformation of the PTT chain leads to spring-like nature along its longitudinal axis which results in high flexibility. For making composites with high strength, PTT should be modified with different fillers. Pristine PTT films are soft and shrinking at low temperatures. When PTT is modified with other polymers or fillers, they exhibit excellent strength, and modulus, high heat deflection temperature, impact strength, and rapid crystallization rate without compromising its features [6]. Table 1 Properties of pristine PTT [7]

Properties

PTT

Tensile strength (MPa)

67.6

Flexural modulus (GPa)

2.76

HDT at 1.8 MP (°C)

59

Notched Izod impact (J/m)

48

Specific gravity

1.35

Mould shrinkage (m/m)

0.02

Melt temperature (°C)

225

Glass transition temperature (°C)

45–75

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4 PTT-Based Polymer Blends A polymer blend is obtained by mixing two or more polymers, and this type of blending creates a new material with different physical properties. The interaction between different macromolecular chains in blends is either secondary intermolecular interaction or partial co-cross-linking. Different types of polymer blends are currently used to overcome the demerits of individual polymers. Polymer blends are classified into three types such as immiscible or heterogeneous polymer blends, compatible polymer blends, and miscible or homogeneous polymer blends [8, 9]. In the first category, different polymers present in the blend exist in different phases the respective glass transition temperatures are observed. In the second group, even though the blend is immiscible, it exhibits macroscopically uniform physical properties, caused by sufficiently strong interactions between the component polymers. The third class of blends is obtained from polymers with similar chemical structures which results in a blend with single-phase and single glass transition temperature. More than 20% of the total usage of engineering polymers is represented by polymer blends. Polymer blends are used in various fields due to their exceptional properties such as high toughness, high elasticity, low cost, lightweight, transparent, and easily processed [10]. PTT polymers have been blended with different types of polymers such as crystalline and amorphous thermoplastics and thermosetting elastomers. The blending of PTT results in several benefits such as lower production expenses, faster development, recycling convenience, and tailored properties [11]. Blends of PTT with crystalline thermoplastics include different blends. One among them is blends with other aromatic polyesters such as PBT and PET. The good processability of PBT and excellent mechanical performance of PET results in materials with excellent surface appearance, high strength and rigidity, and high thermal resistance. Poly(ethylene naphthalate) (PEN) is another polyester used for making blends with PTT. It is an expensive polymer. By making blends with PTT, the cost can be reduced without much compromise in properties [12, 13]. PTT has also formed blends with polyolefin such as linear low-density polyethylene (LLDPE), glycidyl methacrylate (GMA), and metallocene isotactic polypropylene (MIPP). This type of blending results in the improvement of dielectric properties at reduced cost [14–16]. Blending of PTT with polyamide results in thermal and chemical resistant materials with superior mechanical strength [14]. Various amorphous thermoplastics such as polycarbonate (PC), poly(hydroxyl ether of bisphenol A), polyetherimide (PEI) have been used for making blends with PTT. This type of blending helped to decrease moulding shrinkage and enhance dimensional stability. In this type of blend, the chemical stability and mechanical strength of PTT is combined with the impact strength of amorphous polymers [17, 18]. Blends of PTT with thermoplastic elastomers give high impact modification, flexibility, ductility, surface appearance, processability and low notch sensitivity [14].

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5 PTT-Based IPNs Interpenetrating polymer networks (IPNs) are defined as “Polymer comprising two or more networks that are at least partially interlaced on a molecular scale but not covalently bonded to each other and cannot be separated unless chemical bonds are broken” as per IUPAC [19]. Thus, mixtures of different polymers without interlacing are not included in the category of IPN. IPNs are classified into three categories such as sequential, simultaneous, and semi-IPNs. Sequential IPNs are formed by the sequential processing of more than one polymer. Simultaneous processing results in simultaneous IPNs. Polymerization of a monomeric unit in the presence of polymer results in a semi IPN [20]. IPNs generally exhibit high mechanical strength and stability. Hence, two polymers are mixed to form an IPN and we can get material with the properties of both the polymers. This type of synergy can result in the formation of multifunctional materials. Also, the formation of IPN results in an improvement in the existing properties of individual polymers [21].

6 PTT-Based Polymeric Blends—Preparation Methods A polymeric blend is a class of material prepared by mixing two or more polymers to develop new materials with different physical properties. Properties of individual polymer components such as structure, state, and molecular weight as well as the method of preparation, time and temperature of processing, morphology and morphological parameters (size, shape, interfacial area, uniformity, and distribution) and distance between adjacent dispersed particles and adhesion between polymer components determines the properties of polymer blend [21–23]. Almost all-polymer pairs are immiscible, so the blend formation will not take place spontaneously. Several methods can be fabricated to develop blends and composites where the morphology and the mixing process decide its properties. Solution blending, melt mixing, mill mixing, and in situ polymerization techniques can be widely used in addition to latex blending, coagulation spinning methods, and solidstate shear pulverization techniques. Several solid-state processing methods like shear pulverization or cryogenic mechanical alloying provide an effective mixing among the blend which will provide a nanoscale product. This blending process provides an improvement in the product performance like brittleness, modulus and dimensional stability, improve solvent and chemical resistance, improve flame resistance, etc. [22].

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6.1 Melt Mixing Melt mixing is a common method wherein which the components of the blends are mixed in the molten state in batches or extruders. Since organic solvents are not used in this technique, we can say that it is an eco-friendly technique for the synthesis of polymeric blends. Braga et al. [24] synthesised polytrimethylene terephthalate/acrylonitrile–butadiene–styrene (PTT/ABS) blends via melt-mixing method where PTT-g-MA as a compatibilizer and CNTs as nanofillers. The addition of CNTs increases the tensile strength and toughness whereas Young’s modulus decreases. Poly(trimethylene terephthalate) grafted maleic anhydride (PTT-g-MA) as a compatibilizing agent enhances the oxygen permeability of the blend as compared to that of the neat PTT and ABS. The results of high electrical conductivity and gas transport properties are due to the uniform dispersion of the CNTs within the polymer matrix that makes PTT/PTT-gMA/ABS blend-as a promising material for antistatic packaging [24]. Wei et al. synthesized poly(trimethylene terephthalate) (PTT)/maleinized acrylonitrile–butadiene–styrene (ABS-g-MAH) blends where the maleinized ABS copolymer (ABS-g-MAH) is usually used in blending to improve the compatibility of the plastic and ABS. PTT and ABS-g-MAH were mixed together with different weight ratios of ABS-g-MAH/PTT, and it is observed that ABS-g-MAH component served as both a nucleating agent for increasing the crystallization rate and as a toughening agent for improving the impact strength of PTT. Also, the addition of another polymer has an effect in crystallization as well as the subsequent melting behavior of the system [25]. PTT/ABS (Acrylonitrile–Butadiene–Styrene Blends) prepared via melt blending technique without epoxy or styrene–butadiene–maleic anhydride copolymer (SBM) as a reactive compatibilizer can be carried out by drying the PTT and ABS at different compositions and using a 35-mm twin-screw co-rotating extruder with a barrel temperature ranging from 245 to 255 °C and 144 rpm screw speed [26] (Fig. 4).

Fig. 4 Schematic diagram for melt-mixing method [23]

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The immiscible blends of poly(trimethylene terephthalate) (PTT) and polystyrene (PS) were synthesized using the compatibilizer styrene-glycidyl methacrylate (SG) copolymers with various glycidyl methacrylate (GMA) contents. An SG-g-PTT copolymer processed via melt-mixing technique possesses epoxy-functional groups in the SG copolymer that will be able to react with the PTT end groups (OCOOH or OOH). The graft copolymerized, a compatibilized PTT/PS blend formed via in situ, reduces the interfacial tension and increases the interfacial adhesion than that of the uncompatibilized blend [27]. Run, Mingtao et al. studied the glass transition temperature and nonisothermal crystallization of poly(trimethylene terephthalate)/poly(ethylene 2,6-naphthalate) (PTT/PEN) blends. The samples were prepared using the melt-mixing technique, and it was observed that the melting behavior, as well as the crystallization of the binary blends, varies with the composition of PTT and PEN. On varying the composition of the components, the blends exhibit a unique glass transition temperature which concludes that in the amorphous phase PTT and PEN are miscible and at the same time the Tg value decreases with an increase in the PTT content. The different samples of the blends prepared as per the composition of PTT and PEN with the weight ratio of PTT/PEN which was blended as follows: B1, 0/100; B2, 20/80; B3, 40/60; B4, 60/40; B5, 80/20; B6, 100/0. The DSC curve of these samples was analyzed based on the crystallization parameters and cooling rate shown in Table 2 [28], and it is concluded that with an increase in the content of PTT the crystallization rate as well as the degree of crystallinity and its dimension of growth increases [24]. By melt-mixing method poly(trimethylene terephthalate) (PTT) based blends with 30 wt% maleinized poly(ethylene–octene) copolymer (mPEO) can be synthesized which self-possessed two amorphous phases and a moderately crystalline PEO phase. In this blend grafting of PEO was agreed with a commercial maleic anhydride (MA) and dicumyl peroxide as peroxide initiator. The average particle size increases with an increase in mPEO ratio when the blend was processed at low temperature [29]. Table 2 Parameters of PTT/PEN blends during melt crystallization and melting process [28] Samples

Crystallization process

Melting process

Tonset (°C)

Tpl (°C)

TpH (°C)

ΔHc (J/g)

Tml (°C)

Tmll (°C)

ΔHm (J/g)

B1 PEN

–

–

–

–

–

–

–

B2 20PTT/80PEN

220.6

–

211.6

−31.6

–

264.9

38.0

B3 40PTT/60PEN

215.6

–

208.3

−37.9

–

262.4

42.5

B4 60PTT/40PEN

213.9

162.0

204.6

−31.1

219.2

257.0

38.5

B5 80PTT/20PEN

206.6

148.3

201.4

−28.1

222.5

253.5

43.9

B6 PTT

186.7

176.7

–

−50.5

225.5

–

65.9

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Poly(trimethylene terephthalate)-block-poly(tetramethylene oxide) (PTT– PTMO) was synthesized by Szymczyk et al. via the two-step melt polycondensation method. Dimethyl terephthalate (DMT) mixed with 1,3-propanenediol (PD) at a temperature of 160–165 °C in the presence of a small amount of catalyst tetrabutylorthotitaniate (Ti(OBu)4 ). In the second stage, after adding the remaining portion of the catalyst the temperature increased to 220 °C which leads to the separation of completely transesterified product [30]. Jafari et al. used dried pellet of PTT, polypropylene (PP), and maleic anhydride grafted polypropylene (PP-gMAH) with different weight ratios which can be used to develop a PTT/PP blend where PP-g-MAH can be used as a compatibilizer. The melting behavior and the crystallization of these blends are shown to be different, and it is directly related to the PP-g-MAH content in blends [31]. Also, PTT/PP blend prepared via the incorporation of multiwalled carbon nanotubes (MWCNTs) as filler shows an increase in the crystallization temperature and glass transition temperature of the system than that without filler [32]. The enhancement in the property of these blends can be attributed due to the nucleation effect of MWCNTs which emphasizes its need as a filler. Use of nanoclay as compatibilizer in PTT/PP system which can be processed in an intermeshing twin-screw extruder (Berstorff) at a temperature of 200–235 °C shifted the nucleation mechanism from athermal to thermal mode [16]. PTT/m-LLDPE blends with different weight percentages of PTT (75 and 25%) and compatibilizer (0, 2.5, 5, and 10 wt%) were prepared via melt blending in a twin-screw extruder with a screw speed of 100 rpm, and temperature of 230 °C [16]. Poly(ether imide) (PEI)/PTT blends were synthesized in an extruder with variable composition range wherein which the temperature ranges between 260 and 340 °C [33].

6.2 Solution Blending Solution blending is frequently used for the preparation of polymer blends on a laboratory scale. The blend components are dissolved in a common solvent and intensively stirred. The blend is separated by precipitation or evaporation of the solvent. Advantages of the process are rapid mixing of the system without large energy consumption and the potential to avoid unfavorable chemical reactions [34]. The importance of solution blending at high temperature for the inherent phase behavior in the polymeric system was studied using poly(trimethylene terephthalate) bisphenol-A polycarbonate (PTT/PC) blends by Lee et al. In their study, they prepared a set of samples by taking PTT and PC which were dissolved in dichloroactetic acid, and it was cast at 60 °C and another thermally annealed at 260 °C. It is observed that transesterification reactions have happened in PTT/PC blends upon annealing and also the annealed sample shows a homogeneous morphology and amorphous nature [35]. The reported work of Huang et al. showed that thermogravimetric analysis (TGA), polarized light microscopy (PLM) and differential scanning calorimetry (DSC) can be used to analyze the crystallization behavior, miscibility, and melting of

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poly(trimethylene terephthalate) (PTT)/poly(ether imide) (PEI) blends synthesized via solution-blending method. For that, a series of blends were prepared at 80 °C in dichloroactetic acid by varying the composition ratio. All the samples showed single and composition-dependent glass transition temperatures which implies that the blends are completely miscible in the amorphous region [36]. Maila et al. prepared poly(trimethylene terephthalate)/poly(ethylene terephthalate) (PTT/PET) mixture in chloroform/trifluoroacetic acid (CHCl3 /TFA) solution followed by co-precipitation in methanol [37].

6.3 Injection Moulding In injection moulding technique, molten polymeric material pellets are passed through a hopper into a cavity maintained at high pressure. The material is being conveyed forward employing a feeding screw and pushed into a split mold, by filling its cavity through a feeding system with a sprue gate and runners. Figure 5 represents the schematic representation of injection molding. Alper et al. prepared poly(trimethylene terephthalate) (PTT)/poly(ethylene terephthalate) (PET)-blends with microcrystalline cellulose (MCC) were prepared by injection moulding. The powdered MCC with an average particle size of 50 µm imparts reinforcement to the blends. Using a laboratory-scale grinder, PET–PTT blend–MCC compounds were granulated, dried at 105 °C for 16 h followed by the injection moulded into ASTM (American Society of Testing and Materials) test samples [39]. Uncompatibilized β-nucleated PP/poly(trimethylene terephthalate), βnucleated polypropylene (PP)/(PTT) compatibilized with maleic anhydride (MA)grafted PP (PP-g-MA) prepared with a twin-screw extruder at temperatures of 170– 200 °C which was moulded in an injection molding machine. The volume ratio of β-nucleated polypropylene (PP), PTT, and compatibilizer was set up at 70/30/5 [40].

Fig. 5 Schematic diagram for injection moulding [38]

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PTT/CD-PTT blends were prepared; PTT and CD-PTT were prepared by melt spinning in the varying proportion of PTT and CD-PTT in a melt twin-screw extruder at a temperature of 265 °C for 4.5 min at 60 rpm. It was observed that PTT/CDPTT poly-blended with 60:40 and 40:60 shows a maximum melt viscosity value [41]. Poly(trimethylene terephthalate)/metallocene polyethylene (PTT/mPE) blends developed with propylene diene monomer copolymer grafted with maleic anhydride (EPDM-g-MAH) as compatibilizer having the varying concentrations can be prepared in twin-screw extruder operated at a temperature of 260 °C and a screw speed of 100 r/min [42].

7 Ternary Blends Based on PTT Ternary polymeric blends can be prepared by mixing three homopolymers by considering the thermodynamics of mixing and phase separation. Poly(trimethylene terephthalate) (PTT)/polypropylene (PP)/poly(styrene-b-(ethylene-co-butylene)-bstyrene) (SEBS) can be prepared using maleic anhydride-assisted SEBS as compatibilizer precursor. The five different compositions of ternary blends were prepared based on the PP matrix and on varying the dispersed phase ratio of SEBS and SEBSg-MAH. The process was carried out in a barrel of the extruder at different temperature ranges of 230–235–240–245–250–255 °C. Also in all sets of blends, SEBS-gMAH and PP were pre-blended and then extruded with PC and SEBS materials [43]. Poly(trimethylene terephthalate) (PTT) blended with poly(lactic acid) (PLA) using a reactive compatibilizer, poly(ethylene-co-glycidyl methacrylate) (PEGMA) was prepared by a two-step blending process in a melt mixer under N2 gas at a rotational speed of 90 rpm and 240 °C. The sample was quenched in cold water to get an amorphous structure which on annealed at different temperatures (80, 90, 100, 110, and 120 °C) for 1 h to get crystallized product [44]. Ternary blends based on poly(trimethylene terephthalate) (PTT), poly(ethylene terephthalate), and poly(butylene terephthalate) (PBT) was prepared by mixing the three different polymers at different weight ratios using a co-rotating twin-screw extruder, at a screw speed of 60 rpm and a temperature of 280 °C. The crystallization behavior of these different systems shows that the more the PTT content, the larger crystallites formed in ternary blends [45].

8 Polymer Blends Based on PTT for Diverse Applications A new method for the synthesis analogs of PTT, namely poly(neopentylene terephthalate) (PNT), poly(2-methyl-1,3-propylene terephthalate) (PMPT), and poly(2methyl-2-propyl-1,3-propylene terephthalate) (PMPPT), has been reported by Xiang Zhu et al. based on in situ cascade polymerisation [46]. The method employs cyclic oligoesters and diol as monomer and initiator, respectively. The process involves

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Fig. 6 Schematic representation of cascade polymerisation [46]

ring-opening polymerisation (ROP) of the monomer followed by condensation polymerization, Fig. 6. The PTT analogs thus prepared were found to have a higher glass transition temperature than PTT. The effect of PTT fibres as a dispersing agent and polypropylene grafted methyl acrylate (PP-g-MA) as compatibilizer in forming polyblend fibres of polypropylene (PP)/PTT was investigated by Zargar et al. [47]. The melt-spinning process employed for the synthesis of PP/PTT blend fibres was initially modeled using a statistical method response surface methodology (RSM) to obtain a mathematical model in order to predict the mechanical properties of the blend fibres. Nitrogen gas was purged through the compatibilizer and PTT pellets initially at 140 °C for 8 h to prevent hydrolysis and degradation. The blend samples in the form of pellets were prepared using a co-rotating twin-screw-extruder. The production of PP/PTT blend fibres was then done by using the melt-spinning process in a semi-industrial machine. The extruded fibres was then used to prepare Low Oriented Yarn (LOY) fibres at different take-up speeds (1000–1600 m/minute). The evaluation of rheological properties indicated the formation of PTT fibrils in the blend. The study revealed that an optimum amount of 10 wt% of PTT fibres resulted in better mechanical properties as well as improved the crystallinity of polypropylene [47]. In order to improve the electrical properties of composites, conductive fillers can be localized on immiscible polymer blends. In this regard, a co-continuous polymer blend based on polylactic acid (PLA) and PTT was developed initially, and later poly(glycidyl methacrylate) (PGMA)-embedded reduced graphene oxide (RGO) was localized at the interface between the two polymers (PLA and PTT) by melt bending process [48]. The use of conductive fillers like graphene alone can result in agglomeration of the filler in any one of the polymer phases. The use

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Fig. 7 Schematic representation of double percolation and interfacial localization [48]

of compatibilizer containing groups such as glycidyl methacrylate (GMA) helps in improving the interfacial adhesion between the two polymers, thereby aiding the localization of RGO in the co-continuous polymer blend. Figure 7 represents the schematic illustration of the distribution of fillers in binary polymer blends. The effect of multiwalled carbon nanotubes (MWCNTs) as a conductive filler in improving the electrical properties of PTT/PP blends and the application of the conducting blend nanocomposites as electromagnetic interference shielding material (EMI) was reported by Ajitha et al. [49]. The synthetic procedure involved melt mixing of PTT (moisture-free) and PP using a Brabender melt mixer keeping temperature and rotor speed constant at 230 °C and 90 rpm for a period of 10 min. The blends were then compression molded by varying the compositions of PTT and PP and keeping the amount of MWCNTs constant (1 wt%) initially, and later, the effect of varying MWCNT loading was carried out employing the blend 90PTT/10PP. Better EMI shielding property was achieved in the case of PTT (90)/PP (10)/MWCNT (5 wt%) blend nanocomposite due to the double percolation effect of MWCNT and continuous network formation. The impact of fibrillar morphology of PTT/PP blends on the viscoelastic properties was reported by Hajiraissi [50]. PTT/PP blends were prepared by melt blending process using twin-screw extruder in four different ratios PP (99)/PTT (1), PP (94)/PTT (6), PP (90)/PTT (10) and PP (80)/PTT (20), respectively. The blends were then pelletized and extruded using a laboratory extruder (LME-Dynisco). The

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experimental setup of the laboratory extruder was set as the temperature of die and cylinder (195 °C), rotating speed (80 rpm), the distance of die from take-up system (100 cm), and speed of take-up system (10 m/min). The fibre spinning after the melt blending process helped in intensifying the storage modulus, complex viscosity, and elasticity of the fibre samples compared to extruded blends. Diederichs et al. studied the use of PTT in fused deposition modeling (FDM) for 3D printing applications were investigated by forming blends with impact modifier and chain extenders [51]. Initially, PTT was dried to remove moisture content, and the powdered chain extender (CE) poly(styrene-acrylic-co-glycidyl methacrylate) (SAGMA), impact modifier poly(ethylene-n-butylene-acrylate-co-glycidyl methacrylate) (EBA-GMA) were mixed physically to form the blend. The blends were then turned into filaments using a twin-screw extruder at 250 °C and 100 rpm screw speed in co-rotating configuration. The samples for FDM were done employing computeraided design CAD (using CuraLulzBolt Edition software), and printing was accomplished using LulzBoltTaz 6 printer by varying the printing parameters depending on the compositions of blends. The method was successful in developing FDM samples with high impact strength and tensile strength comparable to 3D printed PLA and PET. The study has been found to be highly beneficial in preparing warpage (without any deformation or bending) free samples based on a biobased polymer (partially) such as PTT in place of petroleum-based thermoplastics for additive manufacturing processes [51]. Paszkiewicz et al. synthesized block copolymers of PTT and poly(caprolactone) (PCL) by a two-step process involving transesterification as the first step and polycondensation in the presence of PCL and thermal stabilizer as the second step [52]. The study was proved to be efficient in preparing multiblock polymer with aromatic polyester (PTT) as the rigid segment and aliphatic polyester (PCL) as the flexible segment. The incorporation of flexible segments lowered the tensile strength, melting temperature, and strength at the break while the elongation at break and yielding point exhibited an enhancement. The schematic representation of the two-step process employed is depicted in Fig. 8. The impact of natural rubber (NR) and epoxidized natural rubber (ENR) as impact modifiers was analyzed by the fabrication of elastomeric blends with PTT by Snowdon et al. [53]. The blends were prepared by melt processing in which PTT with moisture content less than 0.5% was melted at 250 °C in a torque rheometer (HAAKE poly lab QC) at 100 rpm screw speed for 2 min. NR and ENR along with reactive compatibilizers such as maleated polybutadiene rubber (MR) and dicumyl peroxide (DCP) were then added to the previously melt PTT and mixed thoroughly for 2 min to obtain the rubber toughened PTT blends. Samples for testing were further processed at the same temperature (250 °C) and screw speed (100 rpm) and finally injection moulded at 30 °C. The mechanical property evaluation of the binary and ternary elastomeric blends prepared by a simple melt compounding process revealed that the impact strength of the ternary blend (PTT/ENR/MR) has 357% gradation compared to neat PTT. The coarse sea–island morphology of the ternary blend and increased crosslink density with submicron level dispersion of particles resulted in improved impact strength.

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Fig. 8 Schematic diagram of two-step synthesis [52]

In another study reported by Kultravut et al. [44], a two-step synthesis was adopted to prepare blends of biodegradable polymer poly(lactic acid) (PLA) and PTT using the reactive compatibilizer poly(ethylene-co-glycidyl methacrylate) (PEGMA). The pre-dried polymer pellets of PTT and PLA were mixed using melt-mixing process (240 °C, 90 rpm) for 5 min to obtain the binary blends of PTT/PLA. Since PEGMA is more reactive toward PLA compared to PTT, the ternary blends were prepared by a two-step procedure in which PTT and PEGMA are premixed in a melt mixer for 2.5 min. PLA was added after the premixing process, and the blending was repeated for another 2.5 min and was quenched immediately to obtain an amorphous structure. The investigation of crystallization behavior, tensile and thermal properties of the annealed, as well as toughened PLA/PTT/PEGMA blends, revealed the formation of a highly crystalline ternary blend system with spherulitic morphology which has resulted in improved tensile and thermal properties. The formation of a miscible blend of PTT in all compositions was done by blending PTT, a semicrystalline polymer with an amorphous polymer, poly(4-vinyl alcohol) (PVPh) by Lee et al. [54]. The blends were prepared by melt blending in an aluminum mold specially designed with a chamber for mixing. The PTT pellets were initially pulverized into finer particles to ensure effective mixing in a shorter time. Mechanical mixing of the polymers was done at 250 °C so that decomposition of PVPh can be avoided, and the whole mixing process was done in an inert atmosphere by the continuous inflow of nitrogen to the chamber. The study has validated the formation of a thermodynamically miscible blend with a homogeneous single-phase morphology as revealed by a single glass transition temperature. The miscibility of the blends over a broad range of temperature, i.e., in the glass state (at low temperature) as well as in the melt state (at high temperature), has been supported by the considerably high interaction parameters such as Florry–Huggins parameter (X12 ) (−0.74) energy density (B) (−32.49 J cm−3 ).

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Copolymer blends based on PTT and poly(ethylene octene) grafted with maleic anhydride and the dynamic rheology analysis was reported in a study by Luo et al. [55]. Dynamic rheology testing helps in determining the interfacial phase analysis of binary/ternary blends, thereby providing an insight into morphology and phase behavior. The toughening agent maleic anhydride attached poly(ethylene octene) (mPOE) was initially synthesized employing a twin-screw extruder having the option for grafting at 200 °C. The blends were prepared in a batch mixer designed with two roller blades which are counter-rotating (Haake, HBI system 90) at 60 rpm for five minutes at 260 °C. Later compression molded samples with 2 mm thickness were prepared under a pressure of 10 MPa at 260 °C. The results indicated that the blends were having maximum miscibility at 240 °C flow temperature and the grafting of maleic anhydride remarkably enhanced the interfacial adhesion as well as the compatibility of the binary blends. Copolymer polyester blends based on PTT by replacing terephthalic acid by 2, 5-thiophene dicarboxylic acid (TFDCA), and a bio-based acid was explored for the synthesis of poly(trimethylene 2,5-dicarboxylate-co-trimethylene terephthalate (PTTTFs) [56]. The synthesis was carried out by a two-step process involving melt polycondensation. TFDCA was made to react with 1,3-propane diol (PDO) in a glass reactor under nitrogen atmosphere at 230 °C for 3 h followed by heating under vacuum at 250 °C to complete the polymerization until rod-climbing effect was observed. The weight molecular weight of the as-synthesized polyesters are greater than 21,000 g/mol; however, the glass transition temperature showed a decrease with increasing TFDCA content. The PTTTFs exhibited higher elongation at break (396%) on account of the β-relaxation and strain-induced isodimorphic crystallisation caused due to strain. The synthesis scheme adopted for the copolyester synthesis is shown in Fig. 9. The synthesis of polyester/polycarbonate (PC) blend based on PTT was carried out to study the effect of changing the composition of blends as well as the key factors affecting phase morphology and crystallization behavior [57]. The blends were prepared by melt-blending process in a mixer (HaakeRheocord 9000) by varying

Fig. 9 Synthesis scheme of copolymer synthesis [56]

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the PTT/PC compositions. Five different compositions of PTT/PC (70/30, 50/50, 40/60, 30/70, 20/80) were chosen and the temperature of mixing (240–280°C), time (5–15 min), rotations per minute (rpm) (60–150 rpm) as well as the shear rate was changed during the melt-mixing process. The melt blends were then removed immediately, converted into sheets of 3–5 mm thickness by pressing and rapidly quenched using ice water in order to freeze the melt state morphologies. The blends were further dried under vacuum at room temperature. The results showed that PTT crystallization is highly influenced by the shear rate, temperature, and mixing time of the blends. PTT fibres commercially sold under the trade name Triexta have been widely employed in textile applications since dyeing of PTT is easier. Moreover, the soft feel, improved stain resistance, and elasticity of PTT fibres have increased the use of PTT fibres in the textile industry. In this regard, PTT/poly(lactic acid) (PLA) blend fibres were prepared using a single screw extruder with PTT content varying from 0 to 50 wt% for textile applications by Padee et al. [58]. The polymers were dried initially (8 h, 80 °C) before compounding. The compounding was done in a twinscrew extruder keeping the barrel temperature and screw speed at 190–250 °C and 50 rpm, respectively. The PTT/PLA blends were further pelletized, dried, and melt spinning in the temperature range 190–250 °C at 50 rpm was done in a single-screw extruder (ThermoHaake) to obtain PTT/PLA blend fibres. The melt spinning was successful in the case of PTT/PLA blend with 10 wt% PTT, because of the different melting temperatures of PTT and PLA at the processing temperature (250 °C). In order to increase the compatibility of PTT and PLA, a terpolymer of ethylene, glycidyl methacrylate, methyl acrylate along a chain extender (Joncryl ADR 4368) containing multifunctional epoxy groups was added to the binary blends during synthesis by Nagarajan et al. [59]. The synthesis was done by reactive extrusion method employing twin-screw micro compounder (Xplore, DSM research) at 250 °C for a short interval of time (2.5 min). The extrudate was then injection molded at 30 °C for 20 s. The influence of processing conditions such as the amount of terpolymer, chain extender as well as screw speed on impact strength and tensile strength was also studied in a mixed-level factorial design experimental model. The study revealed that the tensile strength is mainly influenced by the terpolymer content while the impact strength of the blend is highly affected by all three variable parameters.

9 Interpenetrating Networks (IPNs) Based on Poly(Alkylene Terephthalates) Interpenetrating networks (IPNs) are merged forms of two or more polymers forming a network structure and on a macroscopic scale forming continuous phases. IPNs resemble block copolymers or graft copolymers to a certain extent since there is a bonding between the chains of the two polymers. The concept of IPN was evolved as a method for combining two polymers having different properties and are otherwise

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incompatible in nature. Even though, thermodynamically driven phase separation of the two polymers is feasible, the entrapped or entangled network of the individual polymers hinders the phase separation leading homogeneous molecular level composition. IPNs can be considered superior to polymer blends on account of the less phase separation compared to the extensive phase separation in the case of polymer blends [60]. The synthesis of IPNs generally involve the swelling of a cross-linked constituent in monomer solution in a suitable solvent followed by the polymerisation of the monomer. The domain size of IPNs has a close relation with the length of the polymer chains forming cross-links. The miscibility of the component polymers while forming IPNs is favored by shorter chain lengths [19]. The various parameters such as polymerisation (rate, sequence, compatibility, and mechanism), extent of cross-linking, etc., can be varied during synthesis to produce macromolecular topology of IPNs [61]. The IPNs are generally categorised into six types depending on the synthesis methods as (1) sequential IPNs (2) simultaneous IPNs (3) Latex or interpenetrating elastomeric networks (IENs) (4) thermoplastic IPNs (5) gradient IPNs and (6) semiIPNs [62]. The details of the six different types of IPNs are summarised in Fig. 10. The compatibility between two polymers forming IPNs is enhanced to a certain degree due to the formation of a three-dimensional network structure. Hence, the phase separation between two polymers is significantly reduced in the case of highly compatible polymeric systems. The properties of IPNs can be controlled by factors such as the composition of the component polymers, cross-linking levels, and chemical compatibility of two polymers involved in IPN formation. The method of preparation of polymer blends is generally achieved by melt blending process, whereas the

Fig. 10 Different types of IPNs based on synthesis methods [62]

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synthesis of IPN involves cross-linking and polymerisation. IPNs exhibit a certain degree of co-continuity due to the dispersion of fine droplets (10–100 nm diameter) of one phase in the other phase [63]. The mechanical properties of IPNs with both flexible and stiff networks were studied by Wan et al. [64] by simulation through the coarse-grained molecular dynamics model. The IPNs were designed using the simulation model successfully and the mechanical property evaluation revealed the fact that the stress–strain behavior surpassed the sum of the corresponding individual counterparts. The material with enhanced mechanical behavior was designed by probing the change in mechanical properties upon varying the flexible and stiff components. The formation of IPNs and random copolymer networks (RCNs) is crucial in determining the end applications of polymer blends containing two or more polymers. IPNs are stiffer compared to soft RCNs, and hence, IPNs are widely employed to make automobile parts while RCNs are promising for applications in the field of tissue engineering. A theoretical model was recommended by Chatterjee et al. for devising a scheme for the formation of either RCNs or IPNs. The model was also helpful in determining the ways for tuning the mechanical or thermal behavior by altering the properties especially cross-link density. Two mechanisms have been proposed to explain the growth of polymer networks (Fig. 11). The growth of networks was initiated by submerging a primary gel (the “seed”) in the solvent and monomer mixture. At this stage (stage 0) the monomer diffusion to gel takes place leading to swelling and expansion. During the next stage (stage 1), secondary chain formation due to the polymerization of the monomer happens and the crosslinking of secondary chains leads to IPN formation while RCN is formed due to exchange reactions of secondary chains with the primary gel. The theoretical model was helpful in developing new polymeric systems which are rigid or soft suitable for diverse applications [65]. Thermoplastic-elastomer IPNs based on poly(methyl methacrylate) PMMA and styrene-butadiene rubber (SBR) was synthesized adopting sequential polymerization. The synthesis process involved the preparation of cross-linked SBR initially followed by immersion of the SBR sheets in a homogeneous mix of methyl methacrylate (MMA), divinylbenzene (DVB, cross-linker), and benzoyl peroxide (initiator). Fig. 11 Schematic illustration of the mechanism of formation of IPN and RCN [65]

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The as-obtained swollen samples of MMA were then kept at 0 °C for 3 h followed by in situ polymerization in the oven to obtain flexible SBR/PMMA IPNs. The same method of synthesis was employed in the synthesis of semi-IPNs of SBR/PMMA without using the cross-linker (DVB) during the in situ polymerization of MMA. The IPN has a 50:50 ratio of SBR/PMMA with a service range from −25 to −100 ◦ C, the finest storage modulus, and co-continuous morphology can be possibly explored for vibrational damping applications [66]. The above methods of synthesis can be adapted for the synthesis of IPNs based on PTT for different applications. The progress in the synthesis of PTT can be made use of in developing more IPNs in future for a myriad of applications since IPN formation results in synergistic polymer combinations.

10 Conclusions Poly(trimethylene terephthalate) (PTT) has gained much response as a linear engineering thermoplastic polyester for various industrial applications. The processability and hence the properties of PTT can be significantly improved by blending with other types of polymer or by forming interpenetrating networks (IPNs). The different synthetic procedures employed in PTT blend and IPN synthesis, the influence of various parameters such as morphology, miscibility of polymers, the effect of compatibilizers have been discussed. PTT in combination with other thermoplastics, elastomers, and conductive fillers has expedited the area of applications of PTT-based blends and IPNs in various fields such as damping, electrical, textile, coating, and biomedical applications.

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Chapter 3

Characterization Techniques of PTT-Based Polymer Blends and IPNs V. R. Remya and H. Akhina

1 Introduction Polymer blending is one of the most straightforward, cost-effective, and intriguing approaches for creating highly useful materials with unique properties. A polymer blend is made up of two polymers or copolymers mixed together. Polymer blends are physical combinations of two or more polymers with or without chemical bonding. Polymer mixing is a tempting way to create novel polymeric materials with desirable features without having to synthesize completely new material. Polymer blending also has the advantages of adaptability, simplicity, and low cost. Therefore, polymer blending is a viable means of achieving commercially viable products through special properties or lower costs than would be possible otherwise. Polymer mixes outperform homopolymer compounds in terms of characteristics. Several polymer blends have recently gained a lot of attention due to their diverse properties and applicability in a variety of sectors. Because of their exceptional qualities, poly (trimethylene terephthalate) (PTT)-based polymer blends and IPNs have recently gained a lot of attention [1–5]. PTT is an aromatic polyester produced by polycondensing propane 1,3-diol with terephthalic acid or dimethyl terephthalate. The aromatic polyester poly(trimethylene terephthalate) (PTT) is synthesized by polycondensing 1,3-propanediol (PDO) and terephthalic acid. PTT has been spunbonded on a Hills Inc.-Ason Technologies line and a Reifenhauser (Tandec) line. Extrusion appears to be a reasonably straightforward process based on preliminary research. In many carpet and textile fiber V. R. Remya International and Inter University Centre for Nanoscience and Nanotechnology, School of Energy Materials, Mahatma Gandhi University, Kottayam, India H. Akhina (B) International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. R. Ajitha and S. Thomas (eds.), Poly Trimethylene Terephthalate, Materials Horizons: From Nature to Nanomaterials, https://doi.org/10.1007/978-981-19-7303-1_3

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applications, PTT fibers offer many of the best properties of nylon and polyester and will offer a unique setting for spunbond. PTT research had never gone beyond academic attention until recently, owing to the high cost of its basic material, 1,3propanediol. PTT is now available in industrial quantities thanks to a recent innovation in 1,3-propanediol synthesis (at a lower cost). PTT is polyester that crystallizes quickly. The polymer is an opaque thermoplastic in its solid-state, making it ideal for applications requiring rigidity, strength, and toughness. PTT can be reinforced with surface-modified fillers to make high-strength composites for ETP applications. At low temperatures, PTT films are soft and have a high shrinkage and shrink force. Compounded resins based on the PTT matrix provide an exceptional mix of strength and modulus, as well as high heat deflection temperature, impact strength, and rapid crystallization rate, all while maintaining dimensional stability, electrical insulation, and chemical resistance. In the packaging, textile, and engineering thermoplastic markets, PTT is now a possible competitor of PBT and PET. Despite only being available as marketed polyester for a short time, PTT has attracted both scientific and industrial interest as a result of various in-depth investigations. PTT has a significant tendency to crystallize, and crystallinity has a noticeable effect on the polymer’s performance. A variety of experiments were conducted with the goal of generating structural changes throughout the PTT chain in order to modulate some of the features of the PTT homopolymer, with the copolymerization process being of particular interest [6–18]. The properties of plain PTT are comparable to those of PET and PBT, two other aromatic polyesters. The tensile strength, stretch recovery, morphological, thermal, viscoelastic, dielectric, and surface characteristics of PTT are all excellent. Hence, it is very important and essential to study the various characterization techniques and properties of PTT-based blends and IPNs. Let’s look at some of the most common characterization methods for PTT-based blends and IPNs. The morphological, mechanical, thermal, and viscoelastic properties of PTT-based blends and IPNs may now be examined [4, 11–20].

2 Different Characterization Techniques of PTT-Based Polymer Blends and IPNs 2.1 Structural and Morphological Studies There are good contributions on specialty subjects related to PTT crystallization and crystal morphology including those on spherulite morphology and its evolution during the crystallization process. PTT spherulites were unanimously reported to be of the banded type, presumably due to the numerous lamellae, and throughout the PTT crystallization process, a morphological transition was noted within the spherulites until they reached low temperatures when they transformed to the non-banded kind.

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When the sample thickness and crystallization temperature were reduced, the gap between these bands shrank [21–23]. In order to improve characteristics, increasing the degree of crystallinity is sometimes recommended. This might be accomplished in the case of PTT by introducing chemical agents [24–26], such as organic salts, or by performing self-nucleation therapy. By applying a proper amount of organic salt, a significant improvement in the crystallization rate of PTT was seen at a minimum polymer breakdown cost, based on previous studies. An increase in PTT crystallization temperature led to a decrease in crystallization activation energy and increased crystallinity in a study of PTT self-nucleation therapy. A number of research have been conducted to generate structural changes throughout the PTT chain in order to modulate specific aspects of the PTT homopolymer, with the copolymerization process being of particular interest [26– 30]. PTT was transformed into an unsaturated polyester uniquely, allowing the polymer to become potentially cross-linkable, and so overcome some of its limitations as an ETP, such as low thermal resistance. A significant group of materials is made up of crystalline ETPs and aromatic polyesters. Polyamides, poly(ethylene naphthalate) (PEN), and polyolefins are crystalline ETPs used for this application. Blends of PTT with various polymers such as PET and PBT, poly (ethylene naphthalate), polyolefin, polyamide, polycarbonate, phenoxy resin, polyetherimide, etc. produced various interesting properties such as morphological, structural, mechanical, thermal and viscoelastic, etc. The crystallinity of basic polymers was found to be negatively affected by blending. To reactively change the interface, a low-molecular-weight compatibilizer based on glycidyl methacrylate (GMA) was used. It was effective in lowering the droplet size of the dispersed phase, increasing the interfacial area, and stabilizing the blend morphology (Fig. 1). In PTT blends, cross-connecting density plays a key role in topologies that resemble interpenetrating networks (IPNs) [31]. Lin et al. have studied the surface morphology of β-nucleated PP, uncompatibilized β-nucleated PP/PTT blends, and β-nucleated PP/PTT blends compatibilized with styrene–ethylene–propylene copolymer (SEP) and PP-g-MA by using SEM analysis [32]. The little white particles were found on the smooth fracture surface of β-nucleated PP. TMB-5, a β-nucleating agent that would not melt during the compounding process, was the source of these particles. The dispersed phase of the spherical PTT, with a particle size between 5 and 12 µm, could be seen on the fracture surface of the uncompatibilized β-nucleated PP/PTT blends, and an evident interface occurred between the PTT phase and the b-nucleated PP phase. As a result of the inadequate interfacial bonding between PP and PTT, the compatibility of their mixes with the compatibilizer has to be improved. The particle size of the PTT dispersed phase of the β-nucleated PP/PTT blends compatible with SEP was smaller than that of the uncompatibilized blends, and the particle distribution on the fracture surface was more uniform. The PTT phase and the β-nucleated PP phase were closely linked, and the exposed particles were stretched as well. This could be because SEP’s chain structure was comparable to that of b-nucleated PP and PTT, lowering the interfacial energy between them and promoting good dispersion and uniform distribution of the

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Fig. 1 Surface morphology of PTT/LLDPE (linear low-density polyethylene) 72/25 in the presence of a GMA-based terpolymer: (a) without terpolymer, (b) 2.5 wt % terpolymer, (c) 5 wt % terpolymer, and (d) 10 wt % terpolymer [31]

PTT phase. As a result, SEP was able to effectively compatibilize the β-nucleated PP/PTT blending system. The particle size of the PTT phase fell to 1 µm in comparison to the SEP-modified mix, and the particle distribution on the fracture surface of the β-nucleated PP/PTT blends compatible with PP-g-MA was more uniform [32]. The blends’ fracture surfaces were smooth, and the interfacial bonding between the PTT and PP phases was strong. This could be because the MA group of PP-gMA could react with the hydroxyl group of PTT [33], resulting in much improved interfacial bonding. As a result, PP-g-MA was more beneficial for promoting PP and PTT compatibility. We can conclude from this research that polymer compatibility has a significant impact on improving surface shape and characteristics. The relationship between rheology and morphology of polypropylene/poly(trimethylene terephthalate) mix nanocomposites was investigated by Khonakdar et al. [34] In this work, organoclay particles were preferentially localized at the interface or inside the polyester phase depending on affinity levels, and they acted as a compatibilizer by forming a finer morphology. The functional compatibilizer was found to be very effective at increasing interfacial adhesion and morphological uniformity. By increasing the interlayer distance, the compatibilizer

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also increased the size of the clay gallery. Rheological tests revealed that nanoclay and compatibilizer play a significant role in the system’s complicated viscosity. Similarly, depending on the addition ratio, cross-linking density, IPN structure temperature, nature and quantity of the second phase, structure, hardener, time, compatibility, and so on, PTT blends revealed varied morphologies such as droplet, spherical, lamellar, finer, and so on. Other structural, mechanical, thermal, and other qualities have changed as a result of the varied morphologies. One of the most important is that the morphological and mechanical properties of PTT-based blends are highly correlated. Let us discuss the mechanical properties of PTT-based blends and IPNs in the following section.

2.2 Mechanical Studies The experimental data from the PTT research confirmed that this polymer’s tensile and flexural strengths were higher than PBTs; nevertheless, the latter demonstrated higher impact strength and elongation-to-break than the former. In addition, when compared to PBT, incorporating glass fiber into plain PTT enhanced mechanical characteristics more effectively. The crystallization temperature and yield strain declined as PTT samples aged at room temperature, but the tensile modulus, yield stress, breaking stress, elongation at break, and heat of crystallization increased. The change in glass-transition temperature during annealing is linked to the molecular constraint caused by recrystallization and the mobility of inflexible amorphous PTT chains, according to the researchers [35]. Regarding the performance of recycled PTT [36, 37], it was discovered that after reprocessing in an extruder for up to 4 cycles, Young’s modulus and yield stress of PTT were nearly constant and gradually dropped with subsequent extrusion cycles. They came to the conclusion that the continual loss of break characteristics owing to reprocessing was less than in similar polyesters. Several researches have been conducted to generate structural changes throughout the PTT chain in order to modulate specific aspects of the PTT homopolymer, with the copolymerization process being of particular interest [27–30]. Lin et al. investigated the effect of adding PP to PTT/PP blends on the mechanical properties, namely the tensile qualities. In general, as the PP content increases, the tensile strength at break decreases [32]. The tensile strength at break fell dramatically when the PTT/PP blending ratio was changed from 100/0 to 60/40. PTT and PP binary blends were incompatible and showed poor interfacial adhesion, resulting in low tensile strength. Furthermore, the results for elongation at break show a different trend than those for tensile strength. With the addition of PP, the elongation at break increased. The elongation shifted dramatically from 60/40 to 0/100 mixes. In terms of mechanical qualities, it’s evident that the PP-rich blends had the lowest tensile strength and the maximum elongation at break. Khonakdar et al. investigated the mechanical and morphological properties of polypropylene (PP)/poly(trimethylene terephthalate), (PTT), binary blends in the

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presence of two interfacial modifiers, and two organically modified nanoclay additions. In this work, static mechanical tests in the tensile mode were used to evaluate the specimens, confirming the hypothesis that the higher the PTT concentration, the better the mechanical performance. When a maleated compatibilizer was applied, the compatibilizer-containing blends not only had increased toughness, but also had increased stiffness. In the presence of clay nanoparticles, the tensile modulus was increased much more; however, toughness was sacrificed [34]. The tensile strength of the CNT-filled blend was 70 % higher than that of the unfilled blend. Upadhyay and colleagues used the melt-compounding approach to create PTT/PP blends with and without compatibilizer, as well as nanocomposites [38]. The impact strength and tensile characteristics of the virgin matrix improved after PP was included in the PTT matrix. Similarly, other studies focused on improving the mechanical properties of PTT mixes and IPN for a variety of applications. Morphology, compatibility, temperature, blending ratios, filler content, and other factors have all had a part in toughening, tensile, and impact properties.

2.3 Viscoelastic Properties The properties of blends strongly depend on the structure and morphology of the system, and they are determined by their viscoelastic characteristics. Dynamic mechanical analysis and various types of rheometer such as capillary rheometer, rotational rheometer, etc. can be used to understand the viscoelastic behavior of the polymeric-based materials. Among these, dynamical mechanical analysis (DMA) is a popular method for determining the complex modulus of a material by applying sinusoidal stress and monitoring the strain. To see fluctuations in the complex modulus, the temperature of the sample or the frequency of the stress are frequently changed. It can also be utilized to determine the material’s Tg and to comprehend transitions associated with other molecular movements. The critical capillary number (Cacrit ) and the minimum sphere radius of the dispersed phase (Ra ) are two additional metrics that can provide more insight into the dispersion properties of immiscible blends. The critical capillary number narrates to the point at which the dispersed phase breaks up into smaller sizes due to the continuous phase’s viscous and shear forces exceeding the restoring forces associated with the interfacial tension. The following equation suggested by Wu39 can be used for the calculation of (Cacrit ) and Ra Ca crit

(

ηd =4 ηm

)±0.84

=

γ R a ηm σ

(1)

where ηd and ηm are the viscosities of the dispersed and matrix phases in Pa·s, respectively, γ is the shear rate in s − 1, and σ is the interfacial tension between

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Fig. 2 Rheological effect of the angular frequency on the tanδ of PTT and its blends [40]

dispersed and matrix phases in N·m − 1. The exponent in the equation is positive when ηd/ηm > 1 and negative when ηd/ηm < 1. Rheological properties of binary and ternary rubber-toughened PTT blends have been investigated. On the basis of the tanδ curves (Fig. 2), all samples containing ENR had a value below 1, indicating a gel-like behavior. This gel characteristic may be explained by the cross-linking occurring from the epoxide groups present [40]. The rheological properties of poly (trimethylene terephthalate)/maleinized acrylonitrile–butadiene–styrene copolymer (PTT/ABS-g-MAH) blends were studied. The rheological results show that the melt of all the blends is pseudo-plastic fluid for the apparent viscosity decreased with increasing shear rate. However, the results of non-Newtonian index (n), apparent viscosity, and viscous flow activation energy of the blends melt suggest that the ABS has only a little influence on the rheological properties of the blends [41]. Linear and nonlinear viscoelastic properties of PTT/PP blends prepared through electrospinning and extrusion methods were analyzed. In comparison to the asextruded blend samples, the formed physical fibrillar network led the storage modulus and complicated viscosity to appear as a secondary plateau with amplified values in the low-frequency region [42].

2.4 Thermal Studies DSC analysis can be performed in order to identify their melting (Tm), crystallization (Tc), and glass transition (Tg) temperatures. The following equation can be used to compute the degree of crystallinity (Xc) of the compounds.

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Xc =

ΔH m Wr × ΔH ◦ m

(2)

where Xc is % of crystallinity, ΔHm is the enthalpy of melting, Wr is the weight fraction of the rigid segment content, and ΔH°m is the enthalpy of fusion of complete crystalline compound, which is found to be 146 J/g for PTT. The thermal stability of the PTT-based blends can be analyzed using thermogravimetric analysis. PTT was found to have a two-stage first-order thermal degradation, starting with McLafferty rearrangement of aromatic units and continuing with de-esterification and decarboxylation. It has been reported in the literature that as the PTT level of the blends grew, the thermal stability of the blends decreased; the blend with a greater PP concentration had a higher degradation temperature [43]. DSC analysis revealed two distinct melting peaks for PP/PTT blend [32, 43, 44]. This means that the PP/PTT blend is immiscible, wherein both the polymers show their clear identity. It has been reported that the thermal stability of a PP/PTT blend decreased as the PTT content increased. It can be attributed to a decrease in crystallinity of the blend fibers. The melting and crystallization behaviors of the PTT/PC blends were determined using a Mettler 820 DSC thermal analyzer [45]. The initial heating was done at 10 K/min from room temperature to 270 °C, followed by isothermal heating for 5 min, and the first cooling and second heating were done in a nitrogen environment at 10 K/min. The DSC curves of the unannealed blends(Fig. 3) show two well-defined glass transition temperatures (Tgs), indicating that the system is immiscible. The glass transition temperatures of the amorphous PTT- and PC-rich phases shift to higher and lower temperatures, respectively upon annealing. After annealing at 260 °C for more than 30 min, the two Tg s merged to a single and sharp Tg. Also, the melting temperature (Tm) decreases with the increase of the annealing time imposed on the blends. Then, as the time of annealing extended, the Tm of the blends was found to disappear which indicated the transition from semi-crystalline to an amorphous state. High-temperature annealing leads to the homogenization of the blend. Thermal treatment was shown to trigger a sequence of trans esterification processes that result in a homogeneous system with a stable morphology.

Fig. 3 Melting (second heating) and cooling curve of PTT/PC(70/30) blend [45]

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DSC analysis of PTT/PEI miscible blends was done by [46] DSC thermograms revealed only one single Tg in each of the blend compositions. Both the blend glass transition points and the peak location of cold crystallization exotherm of the crystallizing PTT component in the blends increased monotonously with the increase of PEI content in blends. Changes in cold crystallization temperature are commonly interpreted as evidence of close molecular interaction between crystallizing PTT and stiffer but amorphous PEI polymer chain segments, resulting in PTT chain stiffening and an increase in cold crystallization temperatures. The melt crystallization behavior measurements of ABS-g-MAH/PTT blends were performed [47]. The crystallization peak temperature (Tcp) of neat PTT was the lowest of all samples, and the Tcp of the blends shifted to higher temperature with increasing ABS-g-MAH content from 1 to 5%; and the Tcp values remained unchanged with further increase in ABS-g-MAH content.

2.5 X-ray Diffraction Analysis The crystallinity of PTT-based blends has been reported using the XRD method. The behavior of polymer blend crystallization is vital to understand since the process has an impact on the final blend super molecular structures, as well as their physical and mechanical properties. It can be understood from the literature that as the PTT content increases the percentage of crystallinity decreases. The intensity versus 2θ plot (Fig. 4) of melt-spun fibers of PTT and PP revealed a decrease in intensity of the X-ray diffraction peaks suggesting an increase in the amorphous content, as the PTT content increased [43].

Fig. 4 X-ray diffraction curves of PP/PTT blend fibers [43]

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3 Conclusion This chapter considers the different characterization methods used to analyze the PTT-based blends and IPNs. In the case of blends, a microscopy is an essential tool for understanding the morphology and structure. The morphology of polymer multisystems depends on the method of synthesis and the compatibility of the polymers systems used. All other properties depend on its morphology. Hence, the morphology, mechanical, viscoelastic, thermal, and X-ray diffraction studies of PTT-based blends are briefly discussed.

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19. Nadkarni VM, Rath AK, (2002) In: Handbook of Thermoplastic Polyesters, Fakirov S (Ed), Wiley-VCH, Weinheim 20. Supaphol P, Dangseeyun N, Srimoaon P (2004) Nonisothermal melt crystallization kinetics for PTT/PBT blends. Polym Test 23:175–185 21. Chen M, Chen CC, Ke KZ, Ho RM (2002) Regime crystallization and banded spherulite of poly(trimethylene terephthalate). J Macromol Sci Part B 41:1063–1078 22. Chuang WT, Hong PD, Chuah HH (2004) Effects of crystallization behavior on morphological change in PTT spherulites. Polymer 45:2413–2425 23. Wu PL, Woo EM (2002) Correlation between melting and ringed spherulites in PTT. J Polym Sci Part B 41:80–93 24. Dandurand SP, Pérez S, Revol JF, Brisse F (1979) The crystal structure of poly(trimethylene terephthalate) by X-ray and electron diffraction. Polymer 20:419–426 25. Desborough IJ, Hall IH, Neisser JZ (1979) The structure of poly(trimethylene terephthalate). Polymer 20:545–552 26. Zhang J (2004) Effective nucleating chemical agents for the crystallization of PTT. J Appl Polym Sci 93:590–601 27. Seo YW, Pang KY, Kim YH (2006) Property modulation of poly(trimethylene terephthalate) by incorporation of nonlinear isophthalate unit. Macromol Mater Eng 291:1327–1337 28. Ou CF (2002) Study on poly(oxybenzoate-p-trimethylene terephthalate) copolymers. Eur Polym J 38:2405–2411 29. Chen X, Yang K, Hou G, Chen Y, Dong Y, Liao Z (2007) Crystallization behavior and crystal structure of poly(ethylene-co-trimethylene terephthalate)s. J Appl Polym Sci 105:3069–3076 30. Wei G, Wang L, Chen G, Gu L (2006) Synthesis and characterization of poly(ethylene-cotrimethylene terephthatlate)s. J Appl Polym Sci 100:1511–1521 31. Jafari SH, Yavari A, Asadinezhad A, Khonakdar HA, Böhme F (2005) Correlation of morphology and rheological response of interfacially modified PTT/m-LLDPE blends with varying extent of modification.“ Polymer 46, no. 14: 5082–5093 32. Lin Z, Chen C, Li B, Guan Z, Huang Z, Zhang M, Li X, Zhang X (2012) Compatibility, morphology, and crystallization behavior of compatibilized β-nucleated polypropylene/poly (trimethylene terephthalate) blends. J Appl Polym Sci 125:1616–1624 33. Wang Y, Run M (2009) Non-isothermal crystallization kinetic and compatibility of PTT/PP blends by using maleic anhydride grafted polypropylene as compatibilizer. J of polym. Res. 16:725–737 34. Khonakdar HA, Saen P, Nodehi A, Jafari SH, Asadinezhad A, Wagenknecht U, Heinrich G (2013) On rheology–morphology correlation of polypropylene/poly (trimethylene terephthalate) blend nanocomposites. J Appl Polym Sci 127(2):1054–1060 35. Cho JW, Woo KS (2001) Aging and cold crystallization of melt-extruded PTT. J Polym Sci Part B 39:1920–1927 36. Kalakkunnath S, Kalika DS (2006) Dynamic mechanical and dielectric relaxation characteristics of poly(trimethylene terephthalate). Polymer 47:7085–7094 37. Ramiro J, Eguiazabal JI, Nazabal J (2002) Effects of reprocessing on the structure and mechanical properties of poly(trimethylene terephthalate). J Appl Polym Sci 86:2775–2780 38. Upadhyay D, Mohanty S, Nayak SK, Parvaiz MR, Panda BP (2011) Impact modification of poly (trimethylene terephthalate)/polypropylene blend nanocomposites: Fabrication and characterization. J of Appl. Polym. Sci. 120:932–943 39. Wu S (1987) Formation of dispersed phase in incompatible polymer blends: Interfacial and rheological effects. Polym Eng Sci 27(5):335–343 40. Snowdon MR, Mohanty AK, Misra M (2018) Effect of compatibilization on biobased rubber-toughened poly (trimethylene terephthalate): miscibility, morphology, and mechanical properties. ACS Omega 3(7):7300–7309 41. Ming-tao, R. U. N., W. A. N. G. LI-Xin, C. U. I. Fu-yuan (2010) Mechanical Properties and Rheology Behaviors of PTT/ABS-g-MAH Blends. Polym Mater Sci & Eng 10 42. Hajiraissi R (2020) Linear and nonlinear melt viscoelastic properties of fibrillated blend fiber based on polypropylene/polytrimethylene terephthalate. Polym Bull 77(5):2423–2442

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Chapter 4

PTT/Rubber, Thermoplastic and Thermosetting Polymer Blends and IPNs Rinku Mariam Thomas, Sreedha Sambhudevan, S. Hema, and Arunima Reghunadhan

1 Introduction Polymers with ester as the functional group on the main chain are called polyesters. In industries, the term polyester refers to mainly polyethylene terephthalate (PET) and polybutylene terephthalate [1]. Depending on the chemical structure, polyesters are classified into thermoplastic and thermosetting polyesters. The main source of polyesters is petroleum origin and is typically available in the form of plastics, films and fibers. The utilization of PTT is increasing alarmingly day by day due to its high tensile strength, elastic retrieval, surface belongings, abrasion and chemical confrontation, rate of crystallization and dimensional stability. PTT is highly competitive in the market as they possess mechanical properties similar to PET and processing standards close to PBT [2]. The melt polycondensation of 1.3-propanediol (PDO) with either dimethyl terephthalate (DMT) or terephthalic acid (TPA) leads to the formation of aromatic polyester PTT as shown in Fig. 1. The method is also known as transesterification. The mechanical properties of PTT are almost similar to polyethylene terephthalate (PET), and its processing conditions are close to polybutylene terephthalate

R. M. Thomas American University of Ras Al Khaimah RAK, Ras Al-Khaimah, United Arab Emirates S. Sambhudevan (B) · S. Hema Department of Chemistry, Amrita School of Arts & Sciences, Amrita Vishwa Vidyapeetham, Amritapuri, India e-mail: [email protected] A. Reghunadhan International and Interuniversity Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam 686560, Kerala, India School of Energy Materials, Mahatma Gandhi University, Kottayam 686560, Kerala, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. R. Ajitha and S. Thomas (eds.), Poly Trimethylene Terephthalate, Materials Horizons: From Nature to Nanomaterials, https://doi.org/10.1007/978-981-19-7303-1_4

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Fig. 1 Dimethyl terephthalate +1,3-propane diol giving polytrimethylene terephthalate

(PBT) which makes them highly demanding in thermoplastic market. The dimensional stability, elastic recovery, appealing surface properties, abrasion and chemical resistance make PPT highly promising in the industrial world. One of the major drawbacks of this material is its inherent brittle nature thereby inhibiting its usage as an engineering plastic. In order to tackle this, researchers are focused to impart flexibility to such a system by incorporating elastomers into PTT like thermoplastics so that these rubber-toughened plastics can exhibit superior impact property [3–5].

2 Thermoplastic Blends and Compatibility Among high-performance polymers, thermoplastic elastomers play a vital role due to their exceptional properties like elongation to large extent, easily processable while maintaining the inherent strength. The varieties of thermoplastic elastomers include polyurethanes, polyamides, polyolefins and polyesters. The properties of these multiblock copolymer or polymer blends depend on the ratio of soft and hard segments incorporated in them which alter the crystallinity and thereby tune the mechanical properties [6]. The major challenge in the area of polymeric blends and nanocomposites is the poor interfacial bonding and weak distribution of filler and/or dispersed phase in the polymer matrix. The properties of polymer blends especially mechanical properties are highly dependent on the attractive forces among the immiscible phase boundaries. It is this interfacial region that transfer strains from matrix to reinforcement filler thereby supporting the blend system.

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Literature shows that extensive works have been done in polymer blends owing to their low entropy of mixing of polymers, but phase separation was found to be a serious drawback on such systems [7–9]. To overcome this difficulty, in 1960s researchers introduced a new class of compounds called compatibilizing agents [10]. Its addition in very few quantities improves the adherence between immiscible polymer systems to form perfect polymer blends. This increase in compatibility is in virtue of the presence of certain functional groups which promote interfacial interactions. Typically used compatibilizing agents include maleic anhydride and/or acrylic acid [11]. The compatibilizing agent which is situated on the interface of the two immiscible polymer phases behaves as a surfactant molecule which increases interfacial bonding among the polymer phases by decreasing the interfacial tensions. The blend stability and henceforth the mechanical properties of blend increases when the dispersed phase particle size in a polymer blend becomes more uniform which can be controlled by selecting a suitable compatibilizer. For polymer blends, a number of types of compatibilizers like block, graft and functionalized polymers can be used, and a condition is that it should have the structural similarity of polymers involved in blending [12]. Montanheiro et al. [13] used mechanical mixing method to synthesize a compatibilizer using grafting method where maleic anhydride was grafted to poly(hydroxybutyrate-co-hydroxyvalerate). This is supposed to be another path to prepare low-molecular-weight polymers without affecting their thermal behavior. Polytrimethylene terephthalate/polypropylene blends displayed enhanced interfacial adhesion upon the addition of maleic anhydride-grafted polypropylene (MAPP) as compatibilizer. Zhang et al. [14] found that the properties of HDPE/LLDPE/organoclay composites were influenced by the presence of compatibilizers like HDPE-g-MA, LLDPE-g-MA and a combination of both. The nanocomposites compatibilized with either LLDPE-g-MA alone or an equal concentration of both show better distribution of nanoclay and exhibit better interaction among nanoclay and matrix. The addition of polypropylene-grafted maleic anhydride (PP-gMA) as compatibilizer to PTT/PP blends was studied by Xue et al. and was observed that presence of PP-G MA had a remarkable effect on the crystallization of PTT which is attributed to the interaction between MA andPTT blends. Even though PTT possesses outstanding properties, it comes under the category of brittle polymer with the occurrence of curvatures and sharp notches. PTT suffers low melt viscosity of 200 Pa s (at 260 °C at a shear rate of 200 s−1 ), low heat distortion temperature 59 °C (at 1.8 MPa), poor optical properties and pronounced brittleness at low temperatures. The slow crystallization rate and brittle nature make it difficult for the production of high-performance engineering material. The presence of an elastomeric material or some inorganic particles can bring about some improvement in the toughness notch sensitivity of PTT. The physical properties of PTT can be altered by incorporating another polymer of petrochemical origin thereby enhancing the toughness and making PTT to be developed as an engineering polymer. The useful properties of dissimilar parent polymers can be merged by polymer blending via physical means. Moreover, blending is more economical and

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fast method when compared to other prevalent industrial methods where specialized polymers are produced synthetically. Literature review proves that mechanical properties like impact strength and toughness of PTT matrix have been enhanced by melt-blending method using another appropriate polymer system. PTT/Polypropylene (PP) blends were prepared with PTT at various weight ratios [15], and it was observed that presence of PP does not enhance the mechanical properties of PPT which may be attributed to the discordancy among the polymers and wide gap between the solubility parameters of two systems. The compatibility among PTT and PP was found to increase by using maleic anhydride-grafted polypropylene (PP-g-MAH) [16], and they exhibit better interfacial interaction and mechanical properties which is due to the even distribution of particles in the polymer matrix. In another work, it is reported that elastomeric particles like POE-g-MA and EPDM-g-MA when introduced into PTT significantly improved the toughness of material. These elastomeric/PTT blends possess enhanced properties especially impact strength over the straight PTT and other blends. Polybutylene adipate terephthalate (PBAT) is a random copolyester which is flexible, elastomeric and moreover biodegradable. The precursors for the synthesis of PBAT are terephthalic acid, adipic acid and 1.4-butanediol. PBAT is widely used for food packaging and film applications in virtue of its flexible nature. The viscoelastic properties, impact energy, thermal stability and ductility of PTT can be improved by using PBAT as the toughening agent for PTT blends [17]. These blends possess better impact energy due to the flexible and amorphous nature of PBAT. Nowadays, PTT and PBAT polymers from biological origin have been reported, and they are blended with poly (butylene terephthalate) (PBT) and poly (butylene succinate) (PBS) respectively. PBS/PBAT and PBT/PTT blends show enhanced mechanical properties on the basis of several processing parameters like injection speed, mold temperature, pressure and melt temperature.

3 PTT Thermoplastics and Thermosets In 2007 M. L. Xue et al. showed that in PTT/ABS blend system, DSC thermogram shows two distinct glass transitions which prove that the blends are separated in different phases when they are in the molten state [18]. Tg value at 40–46 °C corresponds to the PTT phase, and that at 100–103 °C corresponds to ABS phase. Upon increasing ABS ratio, increase in TG of PTT occurs, and upon increasing PTT ratio, Tg of ABS decreases. This implies that partial miscibility of PTT in ABS can be enhanced by increasing the ABS content in PTT/ABS blend. The compatibilizers used for the preparation of blend were styrene–butadiene–maleic anhydride (SBM) copolymer and epoxy resin. When epoxy resin was used as the compatibilizer, it was found that the cold crystallization temperature of PTT was increases up to 3 wt% of epoxy content but decreases when the epoxy content reaches 5 wt%. In contrast SBM of 3 wt% possess a similar effect to that of 1 wt% of epoxy showing the enhanced compatibilization of SBM with PTT/ABS blends than the presence of epoxy.

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PTT/PC blend system was analyzed by M. L. Xue et al. and was observed that blending results in declination of mechanical properties due to its reduced miscibility, which can be rectified by using epoxy polymers as compatibilizer where the blends’ interface is reinforced by the crosslinking reactions possible [19]. Up to 2.7 wt% of epoxy in blend creates a decrease in Tg of PTT phase, but as epoxy content was increased further cause a decline in Tg value as revealed from DSC plots. DMA studies show that presence of epoxy polymer leads to an increase in Tg of PTT phase, but Tg of PC phase shows a decline in Tg value. Inferences from mechanical studies are supported by SEM and TEM images where the presence of epoxy is highly influencing the interface positively. Ravikumar et al. prepared PTT/EPDM blends and found that the presence of EPDM hinders the miscibility due to the decrease in crystallinity and enhanced free volume of PTT with EPDM presence. It was observed that interface of blends could be modified by adopting ethylene–propylene monomer-grafted maleic anhydride as compatibilizer. J. M. Huang et al. considered the miscibility and melting behavior of PTT/PEI systems and found that the blends possess single as well as compositional reliant glass transition temperatures for the blend whole composition from DSC data’s [20]. Presence of PEI influences the crystallinity where it decreases from 27 to 3% for 25% blend system, but the crystal growth mechanism remains unaffected. Upon blending, since there is a decrease in specific volume, modulus of elasticity possesses a synergistic character. Huang et al. studied the miscibility, crystallization and melting characteristics of solution-blended PTT/PEI system using PLM, DSC and TGA techniques. PLM technique was employed to study the effects of PEI content and temperature on the PTT crystallization growth rate. Increase in PEI content leads to a decline in spherulite growth which proves that this is a thermodynamically leading procedure. The spherulite growth rate decreases with the increase of the PEI content, implying that it is a thermodynamically dominant process. The optical, crystallization and miscibility behavior of PTT/PBT blends were analyzed by P. Krutphun et al. In the molten state, the blend is highly miscible which is proven by a single and composition-based Tg as given by DSC analysis. When the Tg results were fitted with Gordon–Taylor equation, the obtained fitting parameter of 1.37 indicated the miscibility of blend [21]. Szymczyk et al. studied a series of PTT (rigid)/PEO (flexible) with varying fraction of flexible PEO segments. Three different types of phases exist in this blend system, amorphous PEO-rich phase, semi-crystalline PPT and semi-crystalline PEO phases. The blend system containing 30–70 wt% of PEO shows excellent thermoplastic elastomer characteristics with fairly good thermal steadiness. Presence of PTT in the copolymer system increases the tensile strength and hardness of the system and increases with increase in PTT content [22].

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4 PTT/Rubber Blends (Rubber-Toughened PTT-RTPTT) Blended polymer system guarantees not only improved microstructure homogeneity but also enhanced physical features in terms of mechanical and adhesive characteristics. Beneficial characteristics from multiple parent molecules can be utilized through physical as well as chemical means [23]. When comparing with the direct production of specific polymeric materials blending is a rapid and cost-effective option as well as well a common industrial practice. Research on poly (trimethylene terephthalate) hadn’t ever advanced beyond scientific curiosity until recently, owing to the high cost of its basic ingredient, 1,3-propane diol [24]. However, now it is accessible in commercial quantities attributable to a recent innovation in 1,3-propane diol synthesis at a lower cost via chemical, biological pathways. Implementing rubbery inclusions into PTT to create rubber-toughened composites with better impact strength has been a significant emphasis to counteract the inherent brittleness. The framework of the elastomeric blend during the process of combination has a significant impact on the characteristics of PTT/rubber mix [25].

4.1 Need for Blends In recent decades, combining ductile polymers with impact moderators has led to the emergence of so-called super-tough mixes, which are 10–12 times greater shock resistant. Filling compounding or blending is indeed a quick, easy, yet costeffective technique to alter macromolecules and create new useful polymer composites [26]. As demand for self-sustaining materials grows, there is a move away from petrochemical sources and toward renewable plastics. Aromatic polyester blends, with oneself or other elasto-polymers, have emerged as an advanced intervention among resin producers, processors and, in certain cases, customers. Semi-crystalline aromatic PTT is beginning to outperform their fossil-fuel equivalents in terms of both technological and commercial aspects [27]. The research findings collected from the PTT confirmed that the material has higher tensile and flexural strengths, but decreased shock resistance and elongationto-break. Thus, blending of elastomeric materials can efficiently foster the mechanical properties [28]. Amorphous polymer mixtures make up the majority of engineering polymer blends utilized in automobiles, and the main purpose of combining an elastomeric rubber with PTT is to reduce molding shrinkage and improve structural accuracy. The amorphous structure generally gives high strength and stiffness as well as durability, whereas the crystalline phase of the thermoplastic PTT shows good chemical resistance, mechanical characteristics and melt preparation ease [29].

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4.2 Preparation Methods Mass production of thermoplastic polymer blends can be carried out via meltblending technique; this has been the most flexible approach that has been proven to be eco-friendly as well as economical. The advantage of this approach is that it does not necessitate the use of any types of solvents, However, the drawback is poor dispersion over the rubber matrix, especially at larger filler loadings. This may be due to the increased viscosity of the composites. Extrusion and injection molding were the conventional techniques used for the preparation of these mixes of thermoplastic polymers [30]. Rubbers are commonly mixed to get the best characteristics necessary for the optimal efficiency of commercial products over a defined period of time in a certain environment. The vulcanization process on natural rubber matrix gives exceptional tensile strength and elongation at break as chains of molecules in the elastomer become ordered during deformation activities [31]. The cis configuration of the polymer chain is the primary reason for these kinds of self-reinforcing effects. Toughening of elastomeric materials like rubber is now being advanced by considering the design and properties of their polymeric structures in order to improve the toughness and achieve a rigidity-toughness balance in PTT-based materials with low heat resistance loss. Interfacial adhesion between PTT and rubber and the formation of rubber phase govern the impact resistance of rubber-toughened PTT blends. Toughening of homogenous rubber particles was gone through a microparticle toughening mechanism, and under stacking rubber microparticles concentrate strain and cavitate, allowing polymer matrices to craze or shear yield around [32]. Using compatibilizers to improve interfacial adhesion is a straightforward technique. Some block and graft copolymers are commonly employed as compatibilizers because they may emulsify non-miscible rubber/polymer mixtures and enhance interfacial molecule chain entanglement. DuPont has marketed the biopolymer poly (trimethylene terephthalate, or PTT), which is the result of a chemical condensation process between 1,3-propanediol and terephthalic acid or dimethyl terephthalate (DMT). Susceptibility to fracture can be compensated by toughening, and due to the commercial relevance of PTT blends, it got a lot of attention as it can be produced in a dual-phase structure with soft rubber as the dispersion phase [33]. Jianfeng Wang et al. in 2019 reported that some reactive rubbers like maleic anhydride-grafted ethylene–propylene rubber (EPR-gMA), poly (ethylene-coglycidyl methacrylate) (PEGMA) and glycidyl methacrylategrafted ethylene–propylene–diene rubber (EPDM-g-GMA) were used to improve the interfacial attractive force and hence improved toughening as the active groups present in them will react with polar groups of PTTs [34].

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4.3 Properties The material properties of PTT have been the subject of several investigations; crystalline structure reveals that the aliphatic component of the compound has a strongly twisted gauche–gauche configuration. Triclinic crystalline structure with two chemical repetition units in PTT provides excellent tensile elastic recovery. Jakeway et al. investigated the distortion of PTT and PBT crystalline structures by drawing monofilaments in situ in a wide-angle diffractometer and measuring changes in fiber period d-spacing along the c-axis as a function of strain, and it was found that both of the blends have reversible deformation below their critical stresses to few percentages. Furthermore, the crystal lattice spacing of PTT varies steadily with increasing macroscopic strain, implying that the lattice responds quickly to the applied stress, whereas the crystal lattice of PBT does not alter up to 4% of strain. Three methylene units are organized in a highly contracted and extremely compliant gauche–gauche conformation, which causes tiny reversible crystal chain deformation in PTT [35]. Characteristics of blends are mostly determined by their micromorphological structure within certain measurement circumstances, particularly their interfacial morphological structure, so it is important to understand the structure–property connection to learn more about the toughening mechanism of PTT–rubber mix. The integration between the continuing phase as well as the dispersed phase influences the microstructure of PTT–rubber composites, the construction procedure and shaping conditions on morphology is also important [36]. The soft rubber particle’s primary function in rubber-toughened polymer blends is to increase the plastic deformation of the polymer matrix. The polymer matrix absorbs the majority of the impact energy, with rubber particles dissipating just a minor portion of it. As a result, lowering the polymer content too low reduces the overall impact energy absorption of the mixes. When studying the toughening mechanism in rubber-modified ductile matrices, the critical interparticle distance (IDc) is used to define the transition to super-toughness. The possibility of interparticle distance being unique to each matrix was proposed, but since then, the influence of extrinsic parameters like temperature, strain rate or notch radius, as well as intrinsic parameters like matrix modulus and impact modifier, modulus ratio and interfacial adhesion have been demonstrated or proposed [37]. While going through the studies of Guerrica-Echevarría et al., on the influence of compatibilization on the mechanical behavior of PTT/PEO blends, it was found that the rubber modification improved the compatibility of the mixes, resulting in a smaller dispersed phase size. The reduction was insufficient to achieve the brittle–tough transition, but an increase in the shear rate caused a further reduction in the dispersed phase size and IDc, resulting in extremely high toughness values up to 15-fold the matrix’s notched impact strength at rubber contents over 25 wt% [38]. Many physical probes are available for determining the structures and characteristics of polymer mixtures. However, there are just a few probes available for determining free volume characteristics. Ravikumar developed a unique and nondestructive positron annihilation lifetime spectroscopy (PALS) approach to study

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the consistency impacts between the dispersed and matrix polymer phase of immiscible PTT/EPDM blends by measuring free-volume size and content. As EPDM percentage in the mix increases, concentration, gap or pores between the polymer chain increases, implying that free volumes of EPDM and PTT coalesced to some extent, although phase separation remained. The free volume of these mixes deviated from the established free-volume linear additivity rule in a favorable way. The free-volume parameters of poly (EPM-graftMA) compatible PTT/EPDM blends, on the other hand, were much lower, which was obviously attributable to the stability impact via enhanced contact between blend constituents [39]. The most probable chemical interaction between PTT and poly(EPM-graft-MA) is illustrated in Fig. 2. Acrylonitrile–butadiene–styrene is a widely used industrial macromolecule that has good operability, temperature-humidity resistance and fracture toughness at reduced temperatures. As it has a nice balance of impact strength, modulus, heat and chemical resistance, and abrasion resistance, ABS is a viable candidate for mixing with poly (trimethylene terephthalate). Miscibility and compatibilization studies are necessary to understand the appropriate characteristics of PTT/ABS blends, as the tailor-made features of the finished goods are dependent on the homogeneity between

Fig. 2 Most probable chemical interaction between PTT and poly(EPM-graft-MA) (adapted from Ref. [39])

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the constituents and the phase microstructures of the mix. ABS and PTT were somewhat miscible [30]. On the PTT/ABS blends, both epoxy and SBM demonstrated compatibilization effects, resulting in a change in the PTT-cold phase’s highly organized structure and glass transition temperatures to higher temperatures. The capability of individual components in either immiscible polymer blend was clearly illustrated with the evidence from SEM micrographs as the system with epoxy or SBM compatibilized PTT/ABS blends shows better surface structure.

4.4 Applications To anticipate and improve the material characteristics of blends, it is necessary to understand the nature and underlying factors of blending at the molecular level. Rubber-toughened plastics, also known as thermoplastic elastomers, have been marketed from rubber/plastic mixes. In the packaging, fabric and industrial thermoplastic sectors, PTT is already a possible alternative to polybutylene terephthalate and polyethylene terephthalate [40]. Recently, acrylonitrile–butadiene– styrene, ethylene–propylene–diene monomer rubber, poly(ethylene-octene) elastomer, poly(styrene-b-(ethylene-co-butylene)-b-styrene), and polybutadiene as well as their maleic anhydride-grafted equivalents were verified for toughening for PTT. PTT-Rubber blends are predicted to have a variety of characteristics that will expand the homopolymer’s applicability [16]. Non-reinforced PTT’s application as the desired engineering plastic has been limited owing to its reduced thermal distortion temperature, low melt viscosity, poor optical characteristics and obvious brittleness at low temperatures. Blending polyesters with thermoplastic elastomers have the goal of improving impact modification and reducing notch sensitivity in stiff polyesters. In order to improve the impact performance of engineering, polyesters were reinforced with glass fibers and they are found to be used in automotive and industrial modules [41]. Aside from an increase in notched impact strength, mixing of PTT with thermoplastic elastomers is predicted to improve the characteristics such as flexibility, ductility, surface appearance and processability. EPDM is an ethylene-based elastomer that has long been blended with other thermoplastics to increase impact strength by combining the good processing features of the materials at high temperatures with a wide range of physical qualities of elastomers at service temperatures. The use of a suitable compatibilizer to improve the interfacial adhesion of polymer blends is critical for expanding the range of applications for the blends.

5 PTT-Based Thermosetting and Thermoplastic Blends Through the yardstick of properties, blending and crosslinking polymers are strategic methods to bring forth desirable changes in a polymer. At the molecular level, there

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are stark variations in the constitution of a matrix. A durometric material where two networks are crosslinked, rendering it insoluble in solvents, with no melting yet has a decomposition point. On the flip side, polymer blend in principle is a mixture of un-crosslinked polymers and hence has distinct melting points and has solvents that can selectively dissolve one or both components, which is a farfetched thought, in IPNs. Semi-IPNs may provide solace, in having a suitable solvent for extraction of the non-crosslinked component in the polymer system. In this section, we shall briefly discuss the recent advances in the field of PTTbased thermosetting and thermoplastic blends. Poly (trimethylene terephthalate) (PTT)/Poly (ethylene-butyl acrylate-glyciyl methacrylate) (PTW) blends [42]. A valuable segment of research resides in improving the toughness of materials for various end applications, by reacting together appropriate chemical moieties such as the hydroxyl or carboxyl end group through processing pathways. This blending results in enhanced miscibility with interfacial adhesion elevating the mechanical properties. PTW has been investigated as a copolymer by Wang et al. with positive attributes such as rubber toughening, stemming from the preferential reaction of the glycidyl epoxy groups with the carbonyl and hydroxyl groups. DSC studies have shown that the increased loading of PTW, composition by weight 95/5, 90/10, 80/20 and 70/30 using the twin-screw extruder approach resulted in a nucleation activity permeating through the matrix, increasing the crystallinity of the PTT matrix in PTT/PTW blends. Ranjana et al. have collaborated in the evaluation of morphological-mechanical properties of PBT/PTT blends employing organoclay (Cloisite 30B) as a nanofiller. The study also used an impact modifier such as ultra-low-density polyethylene-grafted glycidyl methacrylate (ULDPE-g-GMA) at a constant proportion in all the blend mixes [43]. Properties were found to be enhanced at an incorporation level of 3 wt% organoclay and 2 wt% modifier, without showing any phase separation. The organoclay was homogeneously dispersed in impact-modified PBT/PTT blends as observed in the SEM studies, and the formation of well-defined spherulites is present in pristine PBT and PTT when Tc was 205 °C. Interesting and relevant studies have been carried out with an objective to fabricate electrically conductive polymer nanocomposites containing carbon nanoparticles incorporated into polyester thermoplastic elastomers based on poly (trimethylene terephthalate) (PTT). Numerous fillers, including organoclay, carbon nanotubes, and graphene oxide, have already been examined for their effects on the structure and physical characteristics of copolymers. This type of segmented block copolymers, based on poly (trimethylene terephthalate) (PTT) as rigid segments and polyether (PTMO) as flexible segments, display a variety of remarkable qualities. The morphology of the carbon nanotubes and graphene nanoplatelets imparts a synergistic influence on the properties such as low glass transition temperature (Tg), the high melting temperature of rigid phase (Tm) and a temperature-independent behavioral response [44]. This is due to the extra stabilization and uniform distribution of nanoparticles in the multiphase structure of the block copolymers (Fig. 3).

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Fig. 3 DSC thermograms for PTT-PTMO and PTT-PTMO/SWCNTs+GNPs nanocomposites during the cooling (a) and second heating (b) [44]

Many studies have dwelled elaborately on the resulting crystallization effect of various polymer systems after blending. Various promoters such as nanomontmorillonite (MMT) have been reported in the literature. The crystallization effects are found to be dependent on the exfoliation of the MMT, rather than the mixing temperature. The finer MMT disperses to create a smoother phase interface [45]. Influence of the surface hydrophobicity of montmorillonite (MMT) (Cloisite® 25A and Cloisite® 30B) on the crystallization behavior of poly(trimethylene terephthalate)/polycarbonate (PTT/PC) blends were studied. The peak crystallization temperature Tc and the apparent crystallization enthalpy ΔHc are shown in Fig. 4. Among a package of properties that exists as a default requirement for engineering plastics or rather “engineered” plastics, barrier properties are very sensitive to structural changes, the oxygen transmission rate (OTR) of the composites was measured, and the results showed that the PTT blends possess a much high oxygen barrier compared to that of the pristine PTT or ABS. Many polymers are immiscible and separate into heterogeneous phases, forming a heterogeneous mixture. To circumvent this issue, certain additives are used to improve their miscibility, which can be minimized using compatibilizers. This imparted a notable effect on the oxygen permeability of the blend compared to that of the neat PTT and ABS [46].

6 Interpenetrating Networks (IPNs): General Outline, Structure and Classification As per the criteria laid down by IUPAC “Polymer comprising two or more networks that are at least partially interlaced on a molecular scale but not covalently bonded to each other and cannot be separated unless chemical bonds are broken” are designated as interpenetrating networks. Interlaced into this synergy of matrices is the synergy of properties that trace their distinction back to individual matrices resulting in a hybrid that surpasses the performance and helps tailor properties as a viable solutions to

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Fig. 4 Peak crystallization temperature Tc and the apparent crystallization enthalpy ΔHc of poly(trimethylene terephthalate)/polycarbonate (PTT/PC) blends [45]

technology applications and challenges. An alternate collection of words describes interpenetrating polymer networks (IPNs) as an entanglement of components that are crosslinked with no existence of covalent bonds, resulting in morphology with distinct phase separation. Hence, IPNs are networks with benefits [47] (Fig. 5). Based on the exclusiveness of the present one or both of the polymer components are interlaced/crossconnected, IPNs are categorized as semi- and full IPNs as shown in Fig. 3. They are prepared by the efficient incorporation of two monomers that are successively or concurrently, polymerized. It is then crosslinked to varying degrees through various pathways. Among the most harnessed methods are the dissolution of a monomeric entity in a polymer network, following which the monomer reactively forms crosslinks to the second interpenetrating network. An alternate route that prevails is in taking into consideration the thermodynamic miscibility of the polymers followed by crosslinking of the polymeric networks. A tried and tested approach to enhance the miscibility of polymers has introduced a class of unique IPNS, where the preparation process hinges on the increase the

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Fig. 5 Representation of interpenetrating polymer networks

compatibility. Such specific polymeric networks called hydrogel IPNs, using water as the solvent, are excluded from the scope of this chapter [48] (Fig. 6).

Fig. 6 a Simultaneous IPN; b Sequential IPN

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6.1 Full IPNs There is negligible bonding between both compounds of a full IPN although they can be fabricated sequentially and simultaneously as shown in Fig. 4. In simultaneous IPN, polymerization and crosslinking of a mixture of two monomers or two linear prepolymers, with phase separation is suppressed due to the rapidly increasing viscosity, while in sequential IPN, a network is swollen in monomers, the subsequent polymerization and crosslinking of which yields an IPN. Phase separation is usually greater for sequential IPN. Since the components are incompatible, structural features within the network control phase segregation. However, there is still phase segregation due to network formation, which leads to small phase domains, which can lead to homogenization of the properties. In IPNs, despite their small domains, the components may have large differences in refractive indices, enabling them to yield transparent materials. The transition from a glassy phase to a rubber phase will become size-dependent for IPNs, and only one transition is predicted as owing to better compatibility [49]. Distribution of phase sizes however produces wide glass transitions (under the influence of temperature and frequency), a property that has been well researched for acoustics and isolation applications [50]. It is observed at temperatures transitional to the Tg of pure components, which is broader than that of neat polymers.

6.2 Semi-IPNs Semi-IPN is characterized by the presence of a single polymer, which exists in a network fashion. In comparison to full IPNs, the presence of a single networked polymer improves miscibility compared to a complete IPN, though compromised in some instances. It is characteristic to observe that if the components are thermodynamically incompatible, there is a higher tendency for phase segregation owing to mobility of the free polymer or the polymer that is not interconnected the glass transition of a semi-IPN, as predicable is between the values of the neat constituent polymers, similar to full IPNs. The well-researched and applied application for semiIPN are as solid polymer-based electrolytes [49, 50] for fuel cells, actuators, among the many avenues that are investigated. The concept of IPNs is a well-received technology because better alternatives for engineered applications are attainable without the need to create a new polymer that synthesize new polymers. In most applications, the polymer molecules are flexible, exhibiting rubber-like properties and dimensional recovery, in spite of large deformations. This dimensional recoverability depends much on the degree of crosslinking of polymeric chains. The modulus increases with the concentration of crosslinks. The expectation holds well for matrices that have undergone a high degree of crosslinking. Below an optimum level of chain network or at very low levels of crosslinking, an

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increase in modulus gives way to a decrease in strength and demonstrates growth in cracks and other failure properties. This is an eventual consequence of a local over-stressing dues to crosslinking and embrittlement of the network structure. Hence, for a given elastomer, a balanced trade-off exists between its stiffness and strength. IPNs are well-arranged/sequenced polymer blends that are devoid of any mediums such as solvents. They depend mainly on their preparation routes and reaction conditions, matrix selection to achieve phase homogeneity. In dealing with incompatible matrices such as organic–inorganic blends, a successful attempt can be made to achieve a homogenous morphology through the IPN approach in spite of some structure–property compromises that are unavoidable [51]. One route to address this trade-off is by modifying the network structure among various other alternative approaches that have shown encouraging levels of application. The technique of mechanically labile bonding used to mitigate the effect of polymer lengths is more pronounced, including chemical moieties in the chains. It helps to effectively highlight and understand the same stress–strain relationships in rubber-based networks.

7 PTT-Based IPNs IPNs are a part of polymer blends where two or more polymers are combined, with at least one of the polymers crosslinked in the presence of the other(s). The interconnection of dual polymer networks provides the privilege to tailor the surface properties resulting in reactivity or specificity aligned with a continuous improvement in the mechanical properties. An important benchmark in the preparation of IPNs is to obtain an identifiable homogeneous phase structure. The benzene monomer ring is a very important moiety for the class of ester-based polymers such as poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), poly(butylene terephthalate) (PBT) and terephthalic acid (TPA) having excellent mechanical properties and processing performance and widely used in various fields [52]. PTT and its chemically modified alternatives are being investigated successively in engineered plastics and textiles. Many novel applications are realized, with PTT-based interpenetrating polymer networks.

7.1 Preparation Methods Polyester is the group of engineered polymers, in which the main carbon chain has an ester moiety. There are varied types of polyester for various applications. Polyester specifically refers to poly (ethylene terephthalate) (PET) and poly (butylene terephthalate). Polyesters are classified as thermoplastic or thermosetting depending on the thermal response of the structural framework with appended moieties. The

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industrial output of polyesters is ever-burgeoning, and the spectrum of applications is ever-widening, given the research and applications that polyesters have catered. Polyesters are made from chemical substances sourced from appropriate fractions in petroleum and are mainly structured into different forms owing to required characteristics such as in fibers, films and plastics. Different polyester monomers are classified and denoted by the existence of methylene groups abbreviated as 2GT, 3GT and 4GT for PET, poly (trimethylene terephthalate) (PTT) and PBT, respectively [53]. PTT had never been researched beyond the limits of academic interest until imminent years of complemented research, as the starting material, 1,3-propane diol, was very expensive to consider for economic purposes. However, a recent breakthrough in 1,3-propane diol synthesis (affordable price tag) has made PTT available in industrial measures, as it has been sourced from cane sugar by a biological process by Dupont [54]. With the dwindling levels in fossil-fuel reserves, the trajectory of interest shifts to other available, low-cost renewable resources. A potent competitor to its own clan, PTT has superseded the PET [abbreviated as 2GT], PBT [as 4GT], respectively, in major engineered thermoplastic markets, such as textiles, molded products and packaging. PTT fulfills the description and demands of an engineered thermoplastic very convincingly showing appreciable tensile strength, stretch recovery and surface characteristics, though the toughness is compromised at times [55, 56]. The gallop of polymeric materials as the pre-eminent candidate in the most technologically viable applications is because it can so successfully improvise. There are several levels of compatibility for a polymer. As we zoom into the structural peculiarities of the compound, thermodynamic compatibility comes to question. The key to solving incompatibilities lies in the preparation techniques of the polymer matrices.

8 Recent Advances in the Preparation of Polyester Traditionally handed down, the formulation of the poly (trimethylene terephthalate) PTT, an aromatic polyester, employs the technique of melt polycondensation of 1,3-propanediol (PDO) with either terephthalicacid (TPA) or dimethylterephthalate (DMT). The reaction is carried out in the presence of hot catalyst like titanium but oxide and dibutyl tin oxide at a temperature of 260 °C. In condensation polymerization, an acid and alcohol are reacted in vacuum, at high temperatures, to form the polyester, then extruded into the form of ribbon and can be further modified to various forms such as pellets, chips or fibers. Chen et al. have elaborated the studies to preparation pathway via solid-state polymerization for the synthesis of poly (trimethylene terephthalate) (PTT) containing phosphorous, whose onset weight loss temperatures were found to increase when analyzed by thermogravimetric analysis in nitrogen and air environments. As per the Flynn–Wall–Ozawa method, thermal degradation kinetics revealed lesser activation energy for the copolyester in comparison to the neat polymer, confirming the weight loss temperature in a nitrogen

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medium is a result of enhanced carbonization. Chemical analysis by spectroscopic techniques confirmed the incorporation of phosphorous in the PTT matrix. A property evaluation of the flammability behavior of the copolyester showed improved flame-retardant properties with the incorporated phosphorous components. Pyrolytic analysis of phosphorus-containing copolyester using Py GC-MS showed that the pyrolysis pattern is not significantly affected by the phosphorus incorporation [53]. Jia et al. studied the catalytic activity of another catalytic system; stannousacetylacetonate for the preparation of PTT was reported. The catalyst successfully influenced the intrinsic viscosity and the ester content, of pure terephthalic acid yielding a degree of esterification to 91% after running the reaction at 260 °C for 2 h. Stannous-acetylacetonate was found to be more ideal and promising than tetra butyl titanate and stannous-octoate for preparing PTT [54]. Shigeru et al. conducted studies on nanocomposites prepared by melt-mixing Poly(ethylene terephthalate) (PET) with graphene or multiwall carbon nanotubes (MWCNT) [55]. The nucleation effect of graphene was found to be more robust than that of MWCNT, as evidenced by the crystallization temperatures. This may be attributed to the enhanced interaction in PET/graphene and creates an environment that aids the formation of crystals with higher perfection. Free-standing films of PTT base matrices are prepared and evaluated. Films were successfully cased by copolymerizing PTT with polyethylene glycol (PEG), as it can greatly attenuate the film formation. The preparation and casting criteria are varied and optimized and eventually help formulate films of various thicknesses. Z. Chen et al. summarized the influences of temperature-induced crystallinity and copolymer composition on the morphology of crystals in PTT blocks in the copolymers [56]. Li Yin et al. studied interesting preparation techniques such as the inclusion of mesoporous silica particles. Poly (trimethylene terephthalate) composites were prepared by hybridization using SBA-15 particles to form a nanostructured composite system. The reaction was carried in situ. The property degradation and the crystallization of PTT can be very aptly channeled to the well-dispersed mesoporous particles [57]. Nanofibrous PTT in the form of electrospun mats was prepared from poly (trimethylene terephthalate) (PTT) with fiber dimensions ranging from 200 to 600 nm (dia). Diamond-shaped structural morphology is favored as the deposition time increased. Khil et al. reported polymer chain mobility was the driving force behind the phenomenon, supported by solvent properties, and point bonding structure [58]. Nanofiber membrane for high flux poly (trimethylene terephthalate) (PTT) for microfiltration purification or separation techniques was prepared and characterized and studied by Li et al. A novel approach combined with a wet-laid process, used for the fabrication of the nanofiber membranes. A two-step strategic pathway was used; firstly, PTT nanofibers were compacted under heat and then local physical crosslinks were introduced by blending PP nanofibers followed by the second heat treatment. Performance properties such as morphology, apparent density, porosity, contact-angle, pore size distribution, water flux and filtration efficiency of the starting

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nanofiber membrane and two modified nanofiber membranes were thoroughly investigated. High rejection rates of above 99.6% were reported, promising tremendous viability for the application of separation membranes for high flux uses [59]. Random copolyesters resulting from PTT and bisphenol-A chemical trans reactions were reported by Sabu et al. The system was skillfully altered by thermal annealing at 260 °C for various times, leading to different amounts of transesterification. Crystallinity was lost in copolyesters annealed for more than 2 h. As annealing progressed, the crystalline characteristics diminished and paved the way to a completely amorphous copolymer [60]. The transesterification pathway has also been studied by, Jian Xiang et al., yielding interesting results in PTT/PBS blends. Transesterification is categorically used as a practical pathway of altering interfacial properties and morphology of the phases in the blended polymer. The mechanical properties of PTT/PBS blends are affected in a slightly negative manner despite their improved phase structure [61]. To effectively bring together blends of PTT and PLA, a reactive extrusion method was adopted, by addition of a terpolymer [EMAGMA- ethylene–methyl acrylate–glycidyl methacrylate], and a chain extender which is epoxy based. The most dictating factor for tensile strength was the addition of the terpolymer, while the impact strength was significantly affected by reactive extrusion conditions. Impact toughening in the blends was positively attributed to reduced particle size and interparticle spacing [62]. Natalia et al. have investigated PTT-based composites [58] with acrylonitrile butadiene styrene (ABS) blend, using maleic anhydride-grafted PTT (PTT-g-MA) as a compatibilizer and carbon nanotubes (CNTs) as reinforcers by melt-mixing. The toughness of the composites was found to increase with the incorporation of the compatibilizer and CNTs, along with a significant increase in conductivity. Preparation pathways create varied structural changes, which in turn affect properties. Once such property of immense application is the barrier properties, which are very sensitive to structural changes. PTT–ABS composites possess a much high oxygen barrier compared to that of the pure matrix of PTT or ABS alone, as evidenced by the oxygen transmission rate [OTR]. Sarathchandran et al. [63] studied nanocomposites containing an additive BADGE, an ether-based plasticizer. Since PTT and the crosslinkable additive were miscible, a melt-mixing technique was successfully affected. The composites are contained containing thermally reduced graphene (TRG). Preparation pathways affected the crystallization of PTT causing phase separation of BADGE and, increased flexibility of PTT was observed. Synergistic improvement in modulus is observed, in the amorphous regions of the PTT composites, at certain specific compositions owing to which a change in morphology is observed. These studies very positively highlight the results of consequence for the design of materials, in which preparation pathways of polymers can be tailored, using a polymer with amorphous regions, for applications where coincident use of an additive-cum-plasticizer creates a plethora of properties and applications.

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9 Characterization Techniques The characterization tools for many polymers help understand the effect and effect of a tailored framework, explaining the properties and performance of the end product. Characterization techniques can be divided into

9.1 Analytical Methods • Morphological studies—scattering (both X-ray and neutron), optical and electron microscopy. • Calorimetry. • Rheological studies. • Thermal analysis. In an interpenetrating network, heterogeneities arise due to thermodynamic compatibility differences. Studies have been for sufficiently small morphological heterogeneities (less than ca. 20 nm), only a single Tg is observed, implying that the composition is unvarying over distances comparable to the range of chain segmental motion. The Tg is found to be intermediate between those of the virgin components. Dynamic rheological studies are carried out the effect of various compatibilizers, employed to increase the blending. Favaro et al. studied the changes generated by the addition of a nanoclay and a terpolymer as a compatibilizer in nanocomposites of poly (trimethylene terephthalate), PTT, and organophilic montmorillonite, MMT. Physical structure analysis such as X-ray diffraction-wide angle (WAXS) and transmission electron microscopy (TEM) studies at elevated temperatures showed the formation of intercalated structures in the nanocomposites without the compatibilizer agent, and complete exfoliation of the platelets of the nanoclay is achieved with the addition of the terpolymer. The polymer system devoid of the compatibilizer developed a percolated network structure. However, the dynamic behavior of the nanocomposites which contain the terpolymer showed that the viscous behavior of the PTT matrix was dominant. In the nanocomposites, PTT/terpolymer/MMT, a full exfoliation level of the nanoclay was obtained. However, the formation of an IPN morphology was observed. The exfoliated nanoclay remained inside the terpolymer phase, thus a percolated network through the PTT matrix was not developed and consequently different rheological properties were obtained for these nanocomposites [64]. An interesting category of copolymers exhibiting isodimorphic behavior based on PTT has been studied, where a double-crystalline polymeric material exhibits a single crystallization and a single melting peak in spite of being double crystalline, as predicted by the Gordon–Taylor equation. Using melt polymerization, copolyesters based on poly (trimethylene terephthalate) is synthesized, consequently characterized by size exclusion chromatography (SEC) and structural parameters revealed through 1 H NMR. Thermal-induced crystallization behaviors and internal crystal dimensions have been studied using DSC, TGA and WAXD and reported. The various analytical

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techniques appropriately confirmed the composition with an increase in TFDCA content, and due to the presence of thiophene ring, the Tg decreased owing to the lesser rigidity of the chains. This might be attributed to the reason that the stability of the thiophene ring was slightly worse than that of the benzene ring due to the presence of sulfur atoms in addition to the β relaxation and strain-induced crystallization [65]. Two major polyester matrices such as PTT and PBT have been widely used in various miscible proportions of blends of poly (trimethylene terephthalate) (PTT) and poly(butylene terephthalate) (PBT) are studied, and the miscibility was proved by the observance of a single temperature transition which is dependent on the composition for every combination of blends between the two ester varieties. In the prepared polymer matrix, as the PTT content increases, cold crystallization set in slowly, pointed by an increase in temperature, while the melt crystallization is found to decrease. The depression behavior is reported to show that the melting (peak) temperature exhibited an inverse relationship as the melting temperature was lowered with increasing content of the other component and pure components formed their own crystals during the process. The blend with 60% by weight of PTT exhibited the lowest apparent degree of crystallinity [66]. Blends of poly (trimethylene terephthalate) (PTT) and poly (butylene terephthalate) (PBT) recorded a single and composition-dependent peak for Tg for all compositions showing good miscibility in these evaluated compositions in an amorphous state. Wide-angle X-ray diffraction results showed that the pure components in the blends crystallized to form separate crystallites, even though the crystallization results suggested simultaneous crystallization of the two components during cooling. The minimum value of the total apparent degree of crystallinity was observed in the blend having 60 wt% of PTT. The apparent degree of crystallinity for each component was found to decrease with the increasing content of the other component. Many advanced techniques have been employed in various studies to successfully elucidate the effect of various preparation pathways of PTT-based IPNs and analytical techniques to probe into the intricacies of the structural framework to explain the performance of the polymer under varied conditions for various applications. Some of the major techniques of characterization that have opened up more avenues of understanding the structural parameters and resulting behavioral analysis have been summarized in the Table 1.

10 Applications With an aliphatic ester as a backbone, poly (ethylene terephthalate) or PET is a polymer that is sought for widespread application in diverse areas. They are investigated for various applications in the form of fillers, fibers and blends mainly. The inclusion of the polyester variations imparts desired enhancement to conductivity, mechanical and permeability properties. It helps project them as for runners in the race for various emerging industrial applications and promising research pathways [77].

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Table 1 Some common techniques employed in the characterization of IPNs Technique

Composition

Reference

Morphological Polarized optical studies—scattering (both microscopy (POM) X-ray and neutron), optical and electron microscopy

PTT/polypropylene blends PTT/carbon nanotube composites

[61, 67–71]

Rheological studies

Capillary rheometry

Poly (trimethylene terephthalate) blends

[70–72]

Spectroscopic studies

1H NMR

Unsaturated aromatic polyesters

[71, 73]

Broadband dielectric and positron annihilation lifetime spectroscopies

Block copolymers

[74]

Dielectric spectroscopy

Semi-crystalline poly (trimethylene terephthalate) (PTT)

[71, 75]

Size exclusion chromatography (SEC) Gel permeation chromatograph (GPC)

PTT copolymers PTT/MIPP conjugated fibers

[60, 72]

Wide-angle X-ray diffraction

PTT/MIPP conjugated fibers

[71, 76]

Differential scanning calorimetry (DSC) Thermogravimetric analysis (TGA)

Bio-based copolyesters [70, 71, 76]

Chromatography

Thermal studies Thermal crystallization kinetics, thermal degradation

Characterization

Focusing on the renewable aspect of the monomer 1,3-propanediol sourced from corn sugar [78], PTT has been well accepted in various ecologically friendly applications such as the textile industry [79]. Alongside the renewability factor, PTT is also found to exhibit tremendous strength and remarkable dyeability [80]. Blending PLA with PTT would develop new material for textile applications. The foray has not been limited to such application, as PTT reached out to a spectrum of applications, with its chemical inertness and stain resistance, owing to the structural parameters and conformations. The highly contracted yet helical conformations cater to the chemical resilience of the matrix. PTT’s optical characteristics, such as transparency and optical loss in nanophotonic devices, are another well-researched area of application. With a relatively large refractive index (1.638), the optical properties are explored to exhibit good transparency in the UV–Vis-IR region, in various photonic devices. The nanofiber fabricated by electrospinning with large surface roughness and length inhomogeneity induces high optical loss. PTT possesses a much small crystal modulus of 2.59 GPa, with enhanced flexibility and a superior elasticity of greater than 90% [81]. Another interesting application is the foray of PTT as a pathway intermediate, in the form of nucleating agents [82, 83], additives [66]. In-depth knowledge of

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structure–property relationship in polymers helps to undertake a course of application in advanced composite materials for high performance. The call is challenged with such materials exhibiting a diversity of properties, with crossinfluences of materials and processing parameters, often partially explained by complex theories based on anisotropy. Typically, these materials either use particle composites with a second phase or fiber-reinforced composites that are layered to form laminates. Each polymeric arrangement is distinct in assembly and properties. Variation in polymeric entities creates immiscible blends/composites, which are heterogeneous. These heterogeneous systems have different mesophase regions, resulting in varied morphology. Tuning the phase dimension is crucial, as in various reports such as the use of MWCNTs acts as a good reinforcing agent and compatibilizer in the otherwise immiscible PTT/PP blend. A “super-combo” effect of multiwalled carbon nanotubes (MWCNTs) in poly (trimethylene terephthalate)/polypropylene (PTT/PP) blend system were studied by Nagarajan et al [62]. MWCNTs served as a reinforcing agent and compatibility for immiscible blends like PTT/PP, which are inherent to the class of Polyesters, which are primarily used in applications requiring a high Young’s modulus. Future materials look promising when using such engineered composites with verified morphology. The structural entities in the PTT polymer provide avenues to be explored in various applications. The flexible methylene units are a key highlight to influence the temperature-induced transitions in a polymer. The introduction of PTT into a stiff chemical moiety helps to alter the Tg and solubility temperature of the copolyesters as it reached a minimum with increasing PTT content. The enhanced flexibility also paves the way to a considerable increase in the impact strength of the blended polymer without sacrificing the Tg. The effect of processing techniques has been investigated for PTT-based fibers. PTT has been studied as a blend with biodegradable poly (lactic acid) PLA. Primarily, the two matrices have been reported to blended in a twin-screw extruder using various feeds of PTT over of range of 0–50% by weight. It was then spun into fibers using the melt spinning technique. The differences between the two matrices were found to be pronounced in their melting characteristics. These differences manifested themselves as a major challenge during the spinning stage of the blends. The “workable” composition was ideally attained at a PTT feed of 10% and 250 C, suitable for the textile application [84]. The tensile properties of the fibers prepared from the PLA/PTT blends increased when increasing PTT percentage and helped prepare a viable fiber for the textile application.

10.1 Applications of the New Generation Polyester PTT The desirable and modified properties of PTT for fiber application are due to the stretch recovery, softness and easy handling, and draping characteristics [85]. With such a desirable pack of properties, they are a primary candidate in the production

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of ready-to-wear, activewear, intimate apparel and inner linings. They also cater to a large number of heavy-duty applications and applications of high wear and tear, such as carpets, which provide values over currently used materials in some market segments and automotive and home upholstery. PTT-based fibers and textiles have high resiliency, newness retention, stain resistance, low static generation, easy dyeing, stain resistance and stretch recovery [86]. Molded goods, viz. transparent heat-resistant bottles with impact strength used in heat and bending-resistant electrical connectors, are made from PTT esters. Another interesting application of PTT is as a property modifier/additive/compatibilizer, imparting flexibility to rigid backbone polymer to form an interesting category of PTT copolymers/blends/composites for varied applications [86–88].

11 Conclusion In the present arena of engineering plastic materials, PTT plays a crucial role as it is a fast-crystallizing polyester with a wide range of applications. The blends of PTT are well suited for applications requiring rigidity, strength and toughness. Indeed, the performance qualities of PTT and the criteria of recyclability drive future attempts to produce and commercialize novel rubber blends of PTT. The incorporation of suitable fillers to the PTT rubber blends improves the mechanical performance, physical characteristics and thermal stability of the polymer without causing a substantial change in its density. In IPNs, the interconnection of a dual polymer network allows the customization of surface characteristics, resulting in increased reactivity or selectivity while retaining the mechanical properties of PTT. As there is a successive investigation around chemically modified alternatives in PTT-IPNs, many novel applications are yet to be realized.

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63. Sarathchandran C et al (2016) Interfacial interactions of thermally reduced graphene in poly(trimethylene terephthalate)-epoxy resin based composites. Polymer 106:140–151 64. Favaro MM, Beatrice CA, Branciforti MC, Bretas RE (2008) Rheological characterization of PTT/MMT nanocomposites 65. Wang G, Jiang M, Zhang Q, Wang R, Liang Q, Zhou G (2019) New bio-based copolyesters poly(trimethylene 2,5-thiophenedicarboxylate-co-trimethylene terephthalate): synthesis, crystallization behavior, thermal and mechanical properties. Polymer 66. Dangseeyun N, Supaphol P, Nithitanakul M (2004) Thermal, crystallization, and rheological characteristics of poly(trimethylene terephthalate)/poly(butylene terephthalate) blends. Polym Testing 23(2):187–194. https://doi.org/10.1016/s0142-9418(03)00079-5 67. Ramachandran AA, Mathew LP, Thomas S (2019) Effect of MA-g-PP compatibilizer on morphology and electrical properties of MWCNT based blend nanocomposites: new strategy to enhance the dispersion of MWCNTs in immiscible poly (trimethylene terephthalate)/polypropylene blends. Eur Polymer J 118:595–605 68. Mathew L et al (2018) Tuning of microstructure in engineered poly (trimethylene terephthalate) based blends with nano inclusion as multifunctional additive. Polym Testing 68:395–404 69. Wu D et al (2011) Electrospinning of poly(trimethylene terephthalate)/carbon nanotube composites. Eur Polym J 47(3):284–293 70. Pisitsak P, Magaraphan R (2009) Rheological, morphological, thermal, and mechanical properties of blends of vectra A950 and poly(trimethylene terephthalate): a study on a high-viscosity-ratio system. Polym Testing 28(2):116–127 71. Inan TY (2017) 2—Thermoplastic-based nanoblends: preparation and characterizations. In: Visakh PM, Markovic G, Pasquini D (eds) Recent developments in polymer macro, micro and nano blends. Woodhead Publishing, pp 17–56 72. Shu Y-C, Hsiao K-J (2006) Preparation and physical properties of poly(trimethylene terephthalate)/metallocene isotactic polypropylene conjugated fibers. Eur Polymer J 42(10):2773–2780 73. Böhme F, Komber H, Jafari SH (2006) Synthesis and characterization of a novel unsaturated polyester based on poly(trimethylene terephthalate). Polymer 47(6):1892–1898 74. Irska I et al (2021) Relaxation behaviour and free volume of bio-based poly(trimethylene terephthalate)-block-poly(caprolactone) copolymers as revealed by Broadband Dielectric and Positron Annihilation Lifetime Spectroscopies. Polymer 229:123949 75. Martín-Fabiani I et al (2013) Dielectric relaxation of poly (trimethylene terephthalate) in a broad range of crystallinity. Polymer 54(21):5892–5898 76. Wang G et al (2019) New bio-based copolyesters poly(trimethylene 2,5thiophenedicarboxylate-co-trimethylene terephthalate): synthesis, crystallization behavior, thermal and mechanical properties. Polymer 173:27–33 77. Korivi NS (2015) 8—Preparation, characterization, and applications of poly(ethylene terephthalate) nanocomposites. In: Mittal V (ed) Manufacturing of nanocomposites with engineering plastics. Woodhead Publishing, pp 167–198 78. Kurian JV (2005) A new polymer platform for the future—Sorona® from corn derived 1,3propanediol. J Polym Environ 13(2):159–167 79. Padee S et al (2013) Preparation of poly(lactic acid) and poly(trimethylene terephthalate) blend fibers for textile application. Energy Procedia 34:534–541 80. Lyoo WS, Lee HS, Ji BC, Han SS, Koo K, Kim SS, Kim JH, Lee J-S, Son TW, Yoon WS (2001) Effect of zone drawing on the structure and properties of melt-spun poly(trimethylene terephthalate) fiber. J Appl Polym Sci 81(14) (2001) 81. Xing X, Wang Y, Li B (2008) Nanofiber drawing and nanodevice assembly in poly(trimethylene terephthalate). Opt Express 16(14):10815–10822 82. Wang C, Fang C-Y, Wang C-Y (2015) Electrospun poly(butylene terephthalate) fibers: entanglement density effect on fiber diameter and fiber nucleating ability towards isotactic polypropylene. Polymer 72:21–29 83. Deshmukh GS et al (2015) Nonisothermal crystallization kinetics and melting behavior of poly(butylene terephthalate) and calcium carbonate nanocomposites. Thermochim Acta 606:66–76

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84. Padee S, Thumsorn S, On JW, Surin P, Apawet C, Chaichalermwong T, Srisawat N (2013) Preparation of poly (lactic acid) and poly (trimethylene terephthalate) blend fibers for textile application. Energy Procedia 34:534–541 85. Padee S, Thumsorn S, On JW, Surin P, Apawet C, Chaichalermwong T, Kaabbuathong N, OCharoen N, Srisawat N (2013) Preparation of poly(lactic acid) and poly(trimethylene terephthalate) blend fibers for textile application. Energy Procedia 34:534–541 (2013). ISSN 1876-6102. https://doi.org/10.1016/j.egypro.2013.06.782 86. Khil MS, Kim HY, Kim MS, Park SY, Lee D-R (2004) Nanofibrous mats of poly(trimethylene terephthalate) via electrospinning. Polymer 45(1):295–301. ISSN 0032-3861. https://doi.org/ 10.1016/j.polymer.2003.09.049 87. Ajitha AR, Mathew LP, Thomas S (2019) Effect of MA-g-PP compatibilizer on morphology and electrical properties of MWCNT based blend nanocomposites: new strategy to enhance the dispersion of MWCNTs in immiscible poly (trimethylene terephthalate)/polypropylene blends. Eur Polym J 118:595–605. ISSN 0014-3057. https://doi.org/10.1016/j.eurpolymj.2019.06.027 88. Ajitha AR, Geethamma VG, Mathew L, Saha P, Kalarikkal N, Thomas S, Strankowski M (2018) Tuning of microstructure in engineered poly (trimethylene terephthalate) based blends with nano inclusion as multifunctional additive. Polym Test 68:395–404. ISSN 0142-9418. https://doi.org/10.1016/j.polymertesting.2018.03.052

Part III

PTT Based Composites and Nanocomposites

Chapter 5

PTT-Based Micro and Nanocomposites: Methods of Preparation and Properties Anju Paul and Sreedevi Krishnakumar

1 Introduction Composite materials can be defined as engineering materials that consists of a combination of two or more phases dispersed separated by a distinct interface. Composites are becoming a part of today’s materials due to the advantages such as low weight, corrosion resistance, high fatigue strength, and faster assembly [63]. The composites can be related to microscopic and nanoscopic scale with different materials based its on size, shape and distribution of two or more phases in the composite [2]. Assimilation of properties of both polymers and micro and nanoparticles to fabricate composites are receiving scientific attention. This impressive technology of designing composites exhibiting desired properties will be benefitted completely only when the resultant value-added products are commercialized. Polymer composites always deliver tailor-made structure property relationship. In addition, when compared to conventional polymers, most of the composites are lighter and this assist in easy formation. Poly(trimethylene terephthalate) (PTT) is a recently commercialized aromatic polyester compared to Polyethylene terephthalate (PET) and Poly Butylene Terephthalate (PBT). It amalgamates the desirable physical properties of poly(ethylene terephthalate) (strength, stiffness, toughness, and heat resistance) with the processing advantages of poly(butylene terephthalate) (low melt and mold temperatures, rapid crystallization), and its good mechanical properties and electrical properties [59, 76]. With the invention of 1,3 propanediol (PDO) in a readily available form, the commercial utility of PTT-based composites became a reality [61]. Inorder to further improve the properties of PTT, numerous studies have suggested the incorporation of reinforcements into modifying the polymer. The micro and nano composites of PTT have greatly improved physical, thermal, rheological, or other properties [29, 31, A. Paul (B) · S. Krishnakumar Sree Sankara Vidyapeetom College, Valayanchirangara 683554, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. R. Ajitha and S. Thomas (eds.), Poly Trimethylene Terephthalate, Materials Horizons: From Nature to Nanomaterials, https://doi.org/10.1007/978-981-19-7303-1_5

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52–55, 73, 75]. The manufacturing of PTT-based composite is rather a difficult task since there are numerous necessities concerning the design, technology, application, and cost-effectiveness. The processing technique is finalized based on the application and it is strongly controlled by the chosen polymer matrix, reinforcement, fiber orientation, volume fraction/weight fraction of filler, density, architecture, and so on. Studies of microcomposites of PTT are comparatively less in number. With the discovery of nanocomposites, research works in last few years are more concentrated on nanocomposites. Nanomaterials such as clay, glycol, sulfides, carbon-based materials like graphene oxide, and carbon nanotube act as potential fillers in PTT matrix. There are numerous synthetic strategies for the preparation of these micro and nanocomposites. Depending on the synthetic methods, properties are varied. Also, there are many preparations are done which could bring about efficient properties for the anticipated applications. This chapter summarizes the recent works in the synthesis of PTT-based micro and nanocomposites in various methodologies and discusses their properties.

2 Synthesis of PTT-Based Composites Numerous studies have done by different groups about PTT-based composites which include both micro and nanocomposites. Synthesis of PTT-based composites is performed in a number of ways such as in situ polymerization, solvent casting, sol– gel technique, injection molding, extrusion process, extrusion-based 3D printing, and melt mixing. Each synthetic methods possess both advantages and limitations. The following sections discusses the synthetic methodologies of both micro and nano composites of PTT (Fig. 1).

2.1 Synthesis of PTT-Based Micro Composites 2.1.1

Injection Molding

When we want to prepare a certain micro composite system with PTT matrix there are several techniques utilized by various researches to obtain improved properties. Melt mixing by extrusion followed by injection molding is one of the most common methods employed for the preparation of PTT microcomposites. This technique involves melting the starting materials to form a viscous melt with the help of a screw inside a barrel. PTT in form of granules or powder along with the filler is fed from a hopper on the screw. It is conveyed along the barrel where it is heated by conduction from the barrel heaters and shear due to its movement along the screw flights. The depth of the screw channel reduces along the length of the screw so as to compact the materials and mix them thoroughly. At the tip of the extruder, the material passes through a die to produce and extrudate shape of PTT and reinforcement melt material

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Fig. 1 Various synthetic methodologies of PTT composites

of the desired shape. Some researchers have used twin screw technology with higher output rates, mixing efficiency, and better heat generation when compared to single screw. The melt mix is passed through injection mold methods to form the final product shape. The PTT composite mix is melted and forced through a nozzle into a relatively cold mold which is clamped tightly closed. When the composite has had sufficient time to cool and solidify, the mold is opened and the article in the desired shape is ejected [2, 17, 30]. The positive history of fiber-reinforced composites as lightweight materials in various engineering structures in the last decades was initiated by the increased production of glass fiber-reinforced plastics (GFRP). Besides the existence of other reinforcement fibers made from carbon or Kevlar, the vast bulk of all fiber-reinforced composites today are still made from glass fibers. One of the reasons for this is the relatively low price of glass fibers compared to other fibers coupled with high tensile strength, high chemical resistance, or electrical insulation making glass fibers the ideal reinforcement for many applications [58]. The manufacturing processes used for PTT are based on melting the polymer by introducing heat and solidifying the polymer–fiber blend after forming. Liu et al. reported the preparation of PTT/chopped glass fiber (CGF) composites by injection molding. Many different compositions of mineral glasses are used to produce micro composites [31]. They possess the combined advantages of high strength with low density and reasonable cost. Composite pellets with 15–40 wt% of

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glass fibers were fabricated using a twin-screw extruder operating at a die temperature of 230–245 °C and a screw speed of 100 rpm. The composite pellets were further subjected to injection molding at a barrel temperature of 235 °C and mold temperature at 35 °C. The glass fiber-reinforced PTT exhibited improved tensile and flexural properties with an increase in fiber content. J. K. Lynch reported the development of a novel, one-step melt-processing method to produce a fiber glass-PTT polymer matrix composite at various concentrations and characterize the mechanical and thermal properties, as well as the morphology [32]. Prior to melt-processing, PTT was dried at 150 °C for about 12 h. Fiber glassPTT components were dry-blended in concentrations varying from 0 to 30 wt % fiber glass in PTT. Dry-blended components were added directly to the hopper of an extruder and melt-processed at 100 RPM, and barrel temperatures were maintained between 240 and 246 °C for different zones and injected into a stainless-steel mold temperature was not controlled and was approximately room temperature. After processing, specimens were conditioned at room temperature prior to mechanical property testing, according to ASTM standards. This novel method produces a FG-PTT composite with superior mixing and tensile strength, as well as enhanced toughness, in one processing step, reducing polymer degradation and fiber attrition, as well as, time, energy, and cost requirements. PTT reinforced with short glass fibers (SGF) has been prepared in a similar way using injection molding [53]. Short glass fibers varying in concentration from 2.5to 30 wt% were incorporated in the PTT matrix using a twin-screw extruder working at a processing temperature of 260 °C and screw speed of 120 rpm/min. The extruded composites have been cooled, chopped, and redried before injection molding. SGF was treated with silane coupling agent prior to the preparation of the composites. This was done to increase the adhesion force between the plastic and fiber. The studies showed that PTT-SGF with 10–20 wt% of the fiber exhibited an increase in crystallization rate, as the SGF acted as nucleating agents for PTT. Carbon fiber consists of small crystallites of turbostratic graphite. One of the allotropic forms of carbon. Carbon fibers are used for reinforcing polymer matrix due to their following properties: (i) very high elastic modulus exceeding that of steel, (ii) high tensile strength, which may reach 7 GPa, (iii) low density of 1800 kg/m3 , (iv) high chemical inertness, (v) good thermal stability in the absence of O2 , (vi) high thermal conductivity, assisting good fatigue properties, and (vii) excellent creep resistance [23, 35, 38]. Researchers all around the world are incorporating various forms of carbon into PTT matrix to improve its properties. Carbon fibers blend the qualities of strength and low density and can be integrated into structural and non-structural components of different materials. Synthesis of injection molded poly(trimethyleneterephthalate)/carbonfiber composites was reported by S. Vivekanandan et al. [68]. The commercially obtained PTT and carbon fibers were melt processed and injected into a mold kept at a pressure of 5 bar and temperature of 25 °C. The composites presented an effective improvement in their thermal and mechanical properties with increase in fiber content, the optimum fiber content being 30 wt%.

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Recycled carbon fibers are more environmentally friendly and sustainable alternative to virgin carbon fibers. Biobased composites of PTT and recycled carbon fiber exhibited improved mechanical properties like flexural, tensile, and impact strength as well as flexural and tensile modulus as a function of the recycled fiber content (10– 40 wt%). Properties like thermal stability, crystallization temperature, and storage modulus also showed significant improvement on incorporation of recycled carbon fiber into PTT. The bio-composites were prepared by melt mixing the precursors at 250 °C at 100 rpm. Later the molten mix was transferred into a preheated injection molding machine and injected into the mold. The desired pressure was kept as 6 bar and mold temperature was kept constant at 30 °C [20]. Glass and carbon fibers reinforced PTT composites have been widely accepted as materials for structural and nonstructural applications. However, these materials pose environmental problems as they are resistant to biodegradation. Natural fibers from plants such as jute, bamboo, coir, sisal, and pineapple are known to have very high strength and hence can be utilized for many load-bearing applications. These fibers have special advantage in comparison to synthetic fibers in that they are abundantly available, from a renewable resource, and are biodegradable [12, 28]. Use of natural fibers as reinforcement is an alternative to recycled carbon fibers which provides the advantages of renewability, safe processability, and economic viability along with the additional advantage of biodegradability. Switch grass is one such natural fiber which has promising tensile properties. Low water/fertilizer requirement of this crop further reduces its cost of production compared to other biomass crops [31, 58]. Injection molding technique was employed for the synthesis of PTT-switchgrass composites, which showed an increase in flexural and tensile modulus than the PTT matrix. The mechanical properties of the composites were further improved by the addition of methylenediphenyl-diisocyanate-polybutadiene (MDIPB) prepolymer and polymeric methylene diphenyl-diisocyanate (PMDI) compatibilizer [50]. Even though the use of natural fibers as reinforcements has the advantage of lower cost and lower density, they have lower thermal stability. As a result, they are suitable as fillers only for polymer matrices with low melting temperatures. Regenerated cellulose fibers, processed from natural cellulose, have higher ductility and thermal resistance compared to their natural counterparts. N. Gemmeke et al. reported the preparation of composites of polybutylenterephthalat (PBT) and polytrimethylentherephthalat (PTT) blends reinforced with regenerated cellulose fibers as well as glass fibers by injection moulding [13]. Composites with regenerated cellulose fillers displayed a significant increase in impact properties in comparison to the composites with glass-fiber filler. This is owed to their longer fiber and ductility. The impact strength and Youngs modulus was observed to increase with increase in fiber content. Use of renewable, biomass-based precursors for the preparation of carbon fillers will help in significantly reducing the cost of production of the composite materials. Biocarbon, the solid material obtained on pyrolysis of biomass, has relatively high surface area, high carbon content (50–80%), and is relatively hydrophobic which makes it a suitable filler for composites. They are more thermally stable than most

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natural fibers and hence offer a wider handling window for mixing with a wide variety of polymer matrices [7, 24, 36, 37, 48]. Lignin, a natural polymer found in plant cell walls, is a potential candidate for the production of carbon fillers because of its high carbon content, natural abundance, and substantial cost advantages [36, 57]. P. Myllytie et al. reported the preparation of PTT composites with carbonized lignin as filler [36]. Carbon filler with 88% carbon content was obtained by thermal treatment of the lignin residue in nitrogen atmosphere. PTT containing 20% of the bio-resourced carbon filler was prepared by extrusion followed by injection molding at selected processing conditions. In a recent work, a value-added green composite was made by the incorporation of biocarbon obtained from peanut hull into PTT matrix [48]. The biocarbon was prepared by subjecting the milled peanut hulls to pulverization in an inert atmosphere at 500 ◦ C. The resultant material along with PTT was injection molded by maintaining the barrel temperature at 250 °C (100 rpm) and a mold temperature at 40 °C. This is an ideal example of valorization of waste biomass through the generation of green composites. When the bio-content increased from 35 to 48 weight percentage, there was improvement in tensile and flexural moduli. Thermochemical conversion of peanut hull to value-added product is possible owing to its enhanced sustainable nature. A schematic representation of the biocarbon synthesis from peanut hull is given in Fig. 2. Incorporation of miscanthus-based biocarbon reinforcement into a PTT-poly (lactic acid) blend matrix is yet another example of using a renewable carbonaceous filler for engineering-plastic-based blends [37]. Table 1 summarizes the synthesis of selected PTT-based microcomposites by injection molding and advantages of the choice of reinforcement.

Fig. 2 Vertical pyrolysis apparatus for biocarbon synthesis [48]

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Table 1 Advantages PTT-based microcomposites prepared by injection molding Sl. No

Composite

Advantage

1

PTT/chopped glass fiber

Improvement in thermal and mechanical [30] properties

2

PTT/short glass fiber

Improvement in tensile strength, Young’s modulus impact strength, and thermal stability

[53]

3

PTT/carbon fiber

Improvement in mechanical properties

[68]

4

PTT/recycled Carbon fiber

Improvement in tensile, flexural, and impact properties

[20]

5

PTT/Biocarbon

Sustainability, lower density, and lower cost

[36, 37, 48]

6

PTT/Natural fibre

Cost-effective, renewable, safe to process, and biodegradable

[13, 50]

2.1.2

References

Melt Mixing

Most techniques used for the fabrication of polymer composites involves two or more heat-intensive steps. Complex processing techniques have several disadvantages including potential degradation of the polymer, agglomeration of the particles during extrusion, change in morphology, increased energy usage, and manufacturing costs. Melt processing is a simple technique used for the preparation of PTTbased microcomposites. J. K. Lynch studied the preparation of fiberglass-reinforced poly(trimethylene)terephthalate composites by one-step, high-shear melt-processing method [32]. The fiber glass filler was shown to serve as a nucleating agent which is indicated by the increase in crystallization temperature of the PTT matrix on addition of the filler. At higher filler concentrations, these composites exhibited superior strength and Izod impact resistance. This novel one-step method also offers cost, time, and energy saving in addition to reduced fiber attrition, polymer degradation, and enhanced mechanical properties. Kiziltas et al. have reported the preparation of microcomposites of poly(ethylene terephthalate)–poly(trimethylene terephthalate)blends with varying levels of microcrystalline cellulose (MCC) filler (0–40 wt%) using melt compounding followed by compression molding [26]. The dynamic mechanical properties of the composite were observed to increase with increase in MCC content. This was attributed to the reinforcement effect of MCC owing to the strong interaction between the cellulose particles and cellulose network.

2.1.3

Extrusion-Based 3D Printing

Three-dimensional (3D) printing, a recently developed technique, is quickly gaining popularity because of its environmental friendliness, lower material and preparation

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Fig. 3 a PTT/BC biocomposites in FFF. b FFF printed samples with different biocarbon content c SEM images of the surface of the FFF printed samples [7]

time requirements [21, 60, 72]. Diederichs et al. reported the preparation of sustainable biocomposites of PTT and miscanthus-derived biocarbon by extrusion-based 3D printing [7]. PTT mixed with biocarbon derived from miscanthus, chain extender, and impact modifier was subjected to extrusion and the obtained samples were then 3D printed using fused filament fabrication technology (FFF). Figure 3 shows the PTT/biocarbon biocomposites with 10wt% and 5wt% biocarbon prepared by FFF and their corresponding SEM images.

2.2 Synthesis of PTT-Based Nano Composites 2.2.1

In Situ Polymerization

Uniform dispersion in nano composites synthesis is a necessity to obtain desirable properties. Many of the synthetic strategies are not attractive as they cannot attain nanocomposites with optimized dispersion of nano additives. The in situ polymerization methodology can control both polymer structure as well as ultimate architecture of the nanocomposites. This process may be initiated either via heat or addition of suitable compounds. Many PTT-based polymer composites can be fabricated by this techniques. Among them, carbon nanofillers covers a broad area since this method

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mostly endorses the fine and uniform distribution of carbon nanofillers such as singlewalled and multi-walled carbon nanotube, graphene, graphite, graphene oxide, and so on [4, 9]. In case of carbon nanotube, there exists a high probability of aggregation owing to its large surface area and Vander Waal’s interactions. Single-walled carbon nanotube/expanded graphite/PTT nanocomposites were prepared by in situ polymerization to study the electrical and optical properties. Carbon nanotube content was varied from 0.025 to 0.5 wt %. The polymerization process was performed in two stages. In the initial step, transesterification between dimethyl terephthalate and bio-1,3 propane diol was done at nitrogen atmosphere followed by polycondensation at a temperature of 260 °C. An ultrasonic homogenizer and a high-speed stirrer were employed to disperse both nanofillers in bio-1,3 propane diol before polymerization process. Viscosity of the resulting mixture was monitored inorder to ensure polymerization. The obtained polymer wires were injection molded in the final step. A significant conductivity improvement was exhibited by the nanocomposites when compared with the neat PTT matrix [45]. In a similar work, Paszkiewicz and coworkers reported the synthesis of PTT-block-poly(tetramethylene oxide) segmented copolymer based nanocomposites containing single walled carbon nanotube and graphene nanoplatelets via in situ polymerization. A significant enhancement in thermal and mechanical properties was obtained by the synergistic effect between graphene and carbon nanotube. Heterogeneous combination of PTT and polytetramethylene oxide provided a stabilized structure for a better uniform distribution of nanofillers in this work. As in the previous work, the dispersion of nanofillers in one of the monomers is done prior to polymerization. Reaction progress was controlled by analyzing the amount of methanol produced, which is one of the by-product of the reaction. The final extrusion was in the form of thin wire and then subjected to injection molding [43]. Szymczyk studied nanocomposites from PTT-block-poly(tetramethylene oxide) segmented copolymer and carboxylic acid functionalized single-walled carbon nanotubes. It was found that thermo oxidative stability of the composite was enhanced by the incorporation of carbon nanotube. Also, melting point of PTT matrix as well as glass transition temperature of polytetramethylene oxide was unaffected by the addition of CNT. There was a significant enhancement in crystallization rate as carbon nanotube acted as nucleating agent. This nanocomposite also synthesized via two-stage polycondensation method. The melt viscosity was monitored in order to estimate the completion of the reaction [66]. Insitu polymerization technique was used to prepare thermoplastic elstomeric composite containing poly(trimethylene terephthalate-block-poly(tetramethylene oxide) copolymer and graphene oxide–Fe3 O4 nanoparticles as fillers. Surface morphological studies of graphene oxide identified its strongly folded curtain shape and inverse chemical co-precipitation method was carried out to synthesize grapheneoxide-Fe3 O4 composite. It is found that Fe3 O4 nanoparticles were thickly dispersed over graphene oxide. Graphene oxide–Fe3 O4 hybrid nanoparticles were found to be superparamagnetic through various characterization techniques. The insertion of nanofillers reinforced the thermoplastic matrix thereby resulting in an improvement in magnetic properties also [67].

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Study by Paszkiewicz et al. used two nanofillers like graphene oxide and reduced graphene oxide in a matrix of poly(trimethylene terephthalate)-blockpoly(caprolactone) copolymer. The work focussed on how the reduction of graphene oxide when compared to non-reduced graphene affect electrical, thermal, and morphological properties. Synthesis of polymer nanocomposites was done by in situ polymerization with the content of 75 wt. % of PTT segments and 25 wt. % of PCL segments. When the nanofillers added to the reaction mixture, polymerization happened in two stages: transesterification and polycondensation. The completion of the reaction is estimated by the viscosity of the sample [40]. In another work, 1,2-propanediolisobutyl(PDIB)-polyhedral oligomeric silsesquioxanes (POSS) is dispersed using ball milling and the reaction mixture was heated at 220 °C after the addition of the catalyst tetra isopropyl titanate. As a result, bis-hydroxypropyl terephthalate was formed in the reactor removing most of methanol [25]. Nanocomposites were extruded out and cut into small chips and purified to eliminate unreacted POSS. The schematic diagram for the synthesis is given in Fig. 4. Table 2 summarizes the synthesis of selected PTT-based nanocomposites by in situ polymerization and advantages of the choice of reinforcement.

Fig. 4 Synthesis of PTT/POSS nanocomposite

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Table 2 Advantages PTT-based nanocomposites prepared by in situ polymerization Sl. No

Composite

Advantage

References

1

PTT/MWCNT/WS2

Improvement in electrical and mechanical properties by low loading of nanotubes

[42]

2

PTT/Graphite nanoplatelets

Variation in conductivity possible by changing the size of graphite platelets

[39]

3

PTT/organoclay

Increase in overall crystallization and crystal size decreased with nanoclay content

[64]

4

Poly(trimethylene terephthalate–block–tetramethylene oxide) (PTT–PTMO)/polyhedral oligomeric silsesquioxane (POSS)

Improvement in thermal stability, increase in hardness due to interfacial interactions

[41]

5

PTT/PTMO/SWNT/Graphene nanoplatelets

Improvement in electrical conductivity

[46]

2.2.2

Extrusion Process

A number of polymer nanocomposites were prepared by this method. A novel maleic anhydride grafted PTT/CNT nanocomposites were synthesized, in which maleic anhydride act as a compatibilizer enhancing interfacial adhesion between matrix and nanofiller. Compatibilzers reduce the interfacial tension in the matrix thereby increasing the interfacial adhesion between dispersed phase and matrix [74]. Also, CNT distribution was facilitated by chemical functionalization by using nitric acid. Carboxylic acid groups are formed on the surface by means of this oxidation reaction. Functionalized CNTs are then composited in PTT matrix by extrusion. Inclusion of CNTs reduces the electrical resistivity of the nanocomposites. The nanocomposites synthesized with 1 wt% of functionalized CNT could bring about electrical resistivity in the range of conductive materials [10]. In a similar work, carbon nanotube dispersion on the polymer matrix is enhanced by the addition of compatibilizer agent, maleic anhydride. In this study, the nanocomposites were prepared by extrusion method. Different compositions of the sample were prepared by varying the concentration of carbon nanotube by means of a twin screw extruder. From the characterization techniques, it is proved that uniform distribution of filler in the matrix resulted in a better mechanical, electrical, and morphological properties.

2.2.3

Melt Mixing

Melt mixing is a fast, cost-effective, eco-friendly, and versatile processing techniques when others are compared. In this method, high shear force is applied which may decline the chances of agglomeration and provides a better dispersion of nanofillers in the matrix. This technique was used to prepare PTT/polyethylene blend and further

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composited with multi-walled carbon nanotube. Melt mixing was done at 60 rpm at 230 °C for 10 min. Thick sheets of the samples were prepared by compression molding. It is found that the introduction of nanofiller enhanced the storage modulus [34].In a similar work, theoretical analysis was done to analyze the selective delocalization of multi-walled carbon nanotube in PTT/PE blend. Melt mixing was the synthetic methodology and it was found that the carbon nanotube associated more with PTT than PE phase. The major reason for this association can be explained by the π–π interactions between aromatic moieties present in PTT and carbon nanotube [27]. In another work, melt compounding was utilized to prepare the nanocomposite in which multi-walled carbon nanotube is used as the filler. PTT was vacuum dried for 14 h prior to compounding. Various amounts ranging from 0.1 to 3% w/w of multiwalled carbon nanotube was added to study mechanical and electrical properties. Incorporation of nanofiller reduced crystal size and improved thermal stability. A significant increase in electrical conductivity is also obtained [14]. Run et al. studied the meling behavior, rheology, and crystallization of PTT/nano CaCO3 composites [55]. It is found that the presence of nano CaCO3 enhanced the crystallization rate of PTT. Combined effect of maleic anhydride grafted polypropylene and multiwalled carbon nanotube on the properties of PTT/PP blends is studied. Strong adhesion between PTT and PP could improve the dispersion of carbon nanotube. Majority of MWCNT is dispersed in PTT phase and only a few amount in PP phase. There was detectable change in morphology as well as electrical properties with the incorporation of MWCNT [51] (Fig. 5).

Fig. 5 Schematic representation of a interaction between MA-g-PP, PTT, and PP, b interfacial action of MA-g-PP in the immiscible PTT/PP blend. Reprinted with permission from [51] Copyright Elsevier

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Sol–Gel Technique

A novel sol–gel synthesis is carried out to prepare PTT/ silica nanocomposites by Bodempudi et al. In this method, PTT pellets were dissolved in trifluoro acetic acid and water with continuous stirring. Then different amounts of tetraethoxysilane were added to get a clear solution. Finally, the solution was dried at room temperature and converted to fine powder using mortar and pestle. The effect of varying amounts of silica on crystallization was studied by taking silica particles in a range of 80– 100 nm. It was found that spherulite size decreased with increase in silica loading but increased with crystallization temperature [3].

2.2.5

Electrospinning

Electrospinning has received much attention in recent years as a method in the fabrication of polymeric fibers. Electrospun fiber mats exhibit considerable potential in a variety of applications because of their high porosity, high surface area-to-volume ratio, and diverse nanostructures [71]. Also, electrospun fibers filled with graphene nanosheets can increase the functional properties of fibers for many applications. It is considered to be a quite innovative technique in case of PTT nanocomposites, as most of the reported syntheses are based on conventional polymerization and melt mixing. PTT/graphene nanosheet solutions were prepared by varying graphene nanosheet amounts in trifluoroacetic acid. Nanocomposites were fabricated by means of electrospinning technique. The prepared solutions were injected by a syringe pump to the nozzle at a controlled flow rate applying high voltage. Further study in improvement in electrical conductivity of fibers could found different mechanism than that of composite films. It is also assumed that the porous structure also influenced the electrical conductivity [18, 19] (Fig. 6).

Fig. 6 Various dispersion types of GNS in PTT fiber [18, 19]

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Ma and Cebe also performed elctrospinning to obtain PTT/ CNT nanofibers and investigated the impact of carbon nanotube on the physical properties of PTT matrix. Phase structure studies confirmed that the model consists of three phases: Mobile amorphous fraction (MAF), rigid amorphous fraction (RAF), and crystalline fraction (C). Enhancement in PTT chain alignment is obtained with the incorporation of carbon nanotube [33].

3 Properties of PTT Composites Many studies prove that incorporation of micro and nanoparticles to semicrystalline structure of PTT resulted in significant improvement in mechanical, thermal, morphological and electrical characteristics. Even though PTT possess excellent elastic recovery, fast crystallization, and comparatively low melting temperature, it is necessary to develop stability and abrasion resistance [5]. Inorder to bring up with efficient functional materials, some desired features like toughness, optical properties, viscosity, and brittleness should be upgraded [49]. High surface area of nanoparticles plays a crucial role in developing functional materials in recent applications. Nano and micro materials like clay, carbon nanotube, graphene, silica, glass fibers, natural fibers, biocarbon, and carbon fibers have been used as fillers in many works. In the current section, various works will be discussed focusing on the enhancement of properties by the inclusion of nano and micro fillers.

3.1 Properties of PTT Microcomposites 3.1.1

Thermal Properties

Knowledge about the thermal behavior of composites has key role in designing their processing techniques and practical applications.

Crystallization and Melting Properties The crystallization temperature and crystallization rate of glass fiber and carbon fiber reinforced composites have been reported to increase with increase in the fiber content till an optimum value is reached, after which it showed a decline [20, 31, 53, 68]. Figure 7 shows the DSC thermogram of PTT-chopped glass fiber composite reported by Liu et al. [29]. The phenomenon of crystallization in polymer composites is controlled by two major factors: (i) the additives will show a nucleating effect which will have a positive impact on the crystallization temperature and (ii) additives can hinder the diffusion and migration of the polymer molecular chains which will cause a decrease in the crystallization temperature [31, 68]. Observations from DSC

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Fig. 7 Differential scanning calorimetric thermograms of PTT composites with chopped glass fiber. Reprinted with permission from [30]. Copyright American Chemical Society

thermograms of the PTT-glass fiber and PTT-carbon fiber composites implies that there is an interplay between these two factors. This inference was further confirmed by the detailed investigation of Run et al. on the kinetics of isothermal crystallization and crystal morphology of PTT/short glass fibers composites [54]. Further, Zhang et al. in their detailed investigation showed that nucleating agents like sodium ionomer of poly(ethylene-comethacrylic acid), disodium p-phenol sulfonate, and disodium p-hydroxybenzoate greatly enhance the crystallization rates of PTT-glass fiber composites [77]. They observed a higher crystallization rate on using either p-phenol sulfonate or a combination of the other two nucleating agents. Petri Myllytie et al. observed that the mold temperature during the injection molding process influenced the crystallization process of the PTT-biocarbon filler composites [36]. At lower temperatures the polymer exhibited cold crystallization transition which disappeared at higher temperatures. This implies that complete crystallization of PTT is attained at higher temperatures. A similar observation was also made in the case of PTT-based biocarbon filler composites reported by V. Nagarajan et al. [37]. Additionally, they showed that the particle size of the biocarbon has an influence on the crystallization process. An increase in enthalpy of cold crystallization and a decrease in calculated percentage crystallinity was observed with a decrease in the particle size range of the biocarbon. The melting temperature of PTT composites depends on the heating rate, crystallization conditions, and thermal history. For PTT at specific heating rate, there was a decrease in melting temperature flowing the addition of glass fiber into the matrix. Glass fibers may act as nucleating agents to promote heterogeneous nucleation, which leads to more defective crystalline defects in limited space [11]. The melting at 217.5 °C was also affected by glass fiber content. Up to 15% addition of glass fiber, it increased, in contrast with adding more glass fiber, it decreased. This should be related with the unstable crystallization during the cooling of PTT. M. Run et al. reported an increase in melting enthalpy with increase in fiber loading for PTT-short glass fiber composites [53]. The melting enthalpy, however,

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decreased after an optimum weight% of the fiber in the composite. Furthermore, a high-temperature re-crystallization exotherm can be observed for all the PTT/SGF composites suggesting that the composites are more likely to perfect crystal reorganization during DSC scanning. Fillers in polymer matrix usually play dual roles, as a nucleating agent to enhance crystallization and at the same time, a hindrance to retard the crystallization. The overall crystallization rate depends on the competition of these two factors. The above melting behaviors in the melting-recrystallization-remelting process are often found when crystalline polymers crystallize non-isothermally from the melt [30, 53, 77].

Thermal Stability Thermal stability of the composites is determined by the type of reinforcement added to the matrix. Studies on the thermal stability of PTT-short glass fiber composites with varying levels of short glass fiber showed that increasing the filler loading improved the stability of the composite [53]. PTT composites with recycled carbon fiber also showed an increase in thermal decomposition temperatures with increase in fiber loading. This was attributed to the better dispersion of the recycled carbon fiber in the matrix and to the strong interaction between the fiber and PTT matrix [20]. Incorporation of microcrystalline cellulose and switch grass fiber showed a negative effect on the thermal stability of PTT composites. A decrease in thermal degradation temperature with increase in concentration of the reinforcement was reported on using microcrystalline cellulose and switch grass fiber as the additive. The lower thermal stability of microcrystalline cellulose and switch grass fiber may be the main reason for the decreased thermal stability of the composites [26, 50].

3.1.2

Thermomechanical Properties

Heat Deflection Temperature The heat deflection temperature is a measurement of a polymer’s resistance to distortion when subjected to a certain load at a high temperature. Filler loading has been shown to increase the HDT of semicrystalline polymers, depending on the type of polymer, its crystallization rate, and the type and amount of filler used. HDT measurements can be used to determine/understand a system’s relative operating temperature in load-bearing components. Liu et al. reported doubling of HDT on addition of glass fiber reinforcement to the PTT matrix. PTT reinforced with both virgin carbon fiber and recycled carbon fiber also showed a significant increase in HDT with increase in the fiber loading [31]. This may be ascribed to the increase in modulus with increase in the fiber content. N. Gemmeke et al. compared the HDTs of PTT reinforced with regenerated cellulose fibers and glass fibers (Fig. 8) [13]. The glass fiber reinforced composites showed the

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Fig. 8 HDT curves of PTT composites. Reprinted from [13] Copyrightwith permission from Elsevier

highest HDT values. This may be due to their higher Youn´gs modulus and a lower softening of the glass fiber itself at higher temperatures. A substantial increase in HDT was also observed when a bio-resourced carbon filler derived from lignin was used as the filler [36]. HDT was observed to increase from 99 °C for the neat PTT to 180–187 °C for 20% bio-resourced carbon-filled PTT composites. The considerable enhancement in HDT is owed to the increased crystallinity of the PTT matrix due to the nucleating effect of the filler as well as reinforcing action of the filler. J. P. Reddy et al. reported an increase in HDT for PTT reinforced with natural fiber. HDT of the composite showed an improvement from 62 to 194 °C on the addition of 35 weight % switch grass fiber [50]. Several studies have shown that the HDT of thermoplastics can be improved by incorporating natural fibers as reinforcements. HDT can also be influenced by processing conditions. V. Nagarajan et al., in their study on PTT-biocarbon composites, observed that even though the filler content had little effect on the HDT, it was substantially increased on increasing the mold temperature during the preparation of the composite [37]. The increment in HDT values can be assigned to increase in percentage of crystallization of PTT and increased stiffness with increase in mold temperature.

Dynamic Mechanical Properties of Composites Dynamic mechanical analysis is an indispensable technique for the understanding the relationships between various viscoelastic properties like storage and loss moduli, mechanical damping parameter, dynamic viscosity, and temperature. Addition of

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reinforcements to polymeric material has been reported to increase the storage modulus of the material [1, 6, 22, 47, 57]. S. Vivekanandan et al. reported an increase in storage modulus of PTT/carbon fiber composites with varying amounts of the fiber [68]. The storage modulus was observed to increase as a function of fiber concentration in the composite. Similar behavior was also observed when glass fiber, recycled carbon fiber and switch grass fiber were used as reinforcements [20, 50, 68, 69]. Incorporation of fillers into the polymer matrix increases their stiffness to a large extent, which leads to a rise in the modulus. Interaction between the fibers and the PTT matrix results in an increase in the elasticity and decrease in the viscosity of the material. Therefore, less energy will be utilized to overcome the friction forces between molecular chains which decrease the mechanical loss [20, 69]. Microcrystalline cellulose-filled composites of PET–PTT blend also showed an increase in storage modulus with increase in filler content. Stress is more evenly distributed throughout the composite on increasing the microcellulose content, thereby increasing the modulus. Moreover, strong interaction between the matrix fibrils and cellulose molecules due to hydrogen bonding also contributes to an increase in storage modulus [26].

3.1.3

Rheology

Rheological behavior of polymeric materials greatly depends on the interactions between the fillers and the matrix and this can influence the processing parameters and properties of the composites obtained. M. Run and co-workers have discussed the rheological behavior of composites containing short carbon fibers in PTT-based matrices in two different literature reports [53, 56]. PTT-short glass fiber composites exhibited a complicated rheological behavior. The composite melt exhibited a dilatant fluid behavior at lower shear rate and a pseudo-plastic fluid behavior at higher shear rate. An increase in the fiber content lead to a decrease in melt apparent viscosity of the composites as the rigidity of the fibers improves the flowrate of the melt [53]. Short glass fibers incorporated in PTT-maleinized acrylonitrile–butadiene–styrene (ABS-g-MAH) blend showed a pseudo-plastic fluid behavior [56]. The melt apparent viscosity of these composites was observed to increase with increase in the fiber content. The apparent viscosity was lower than neat PTT as the short carbon fibers can diminish the entangling of the polymer chains and the melt flow resistance is reduced due to the self-lubricity of the reinforcing fibers. V. Nagarajan et al. showed that size fractionated biocarbon incorporated PTT showed an increase in viscosity compared to neat PTT [37]. The viscosity showed a dependency on size of the biocarbon, with particles in the size range of 20–75 µm showing highest viscosity. This behavior has been ascribed to various reasons including selective adsorption of the polymer chains on the surface of the biocarbon particles, increase in the excluded free volume around the particles and reduced polymer chain entanglement.

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Mechanical Properties

The importance of fiberreinforced composites stems mostly from the large increase in strength and modulus, which offers a promising application for composites. Glass fiber- reinforced composites showed a significant enhancement in their tensile strength, impact strength, flexural strength as well as tensile and flexural moduli on increasing the fiber loading [30]. Tensile properties and impact strength of glass fiber-reinforced PTT composites with varying content of glass fiber are shown in Fig. 9. Similarly, PTT-short glass fiber composites reported by Run et al. showed an improvement in impact strength, tensile strength and Young’s modulus [53]. The enhancement in rigidity and toughness of the composite is attributed to the strong interaction between the PTT matrix and the short glass fiber modified with silane coupling agent. The best results were obtained for fiber loading of 10–20%. This is possibly due to short glass fibers overlapping each other at higher loadings which is useful in for stress transfer and carrying capacity. PTT composites reinforced with regenerated cellulose fibers showed a noteworthy improvement in impact properties in comparison to their glass fiber counter parts owing to longer fiber length and ductility [13]. These composites showed an additional enhancement in Charpy impact strength on using maleic anhydride grafted polyethylene as an additive (Fig. 10). On using micro cellulose as a reinforcement, PTT showed an increase in tensile strength owing to better stress transfer properties. Tensile and flexural moduli of the composites were observed to increase as a function of the fiber content in the composites. PTT reinforced with carbon fiber showed significant improvement in their mechanical properties [68]. Flexural, impact, and tensile strengths of the composites increased by 30, 60, and 120 weight %, respectively, for 30 weight % fiber loading. The good adhesion between carbon fibers and the PTT matrix may be the possible reason for this enhancement in mechanical properties. Same trend was observed for recycled carbon fiber-reinforced PTT composites reported by Jacob et al. [20]. Reddy et al. demonstrated that while using a natural fiber like switch grass as reinforcement, addition of compatibilizers is required for the material to show an improvement in mechanical properties [50]. Compatibilizers like polymeric

Fig. 9 Tensile properties and impact strength of glass fiber reinforced PTT composites. Reprinted with permission from [30]. Copyright American Chemical Society

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Fig. 10 Force–deformation curves and energy-deformation curves of the notched Charpy impact tests of the neat PTT matrix materials and their composites with 30 wt% fibers. Reprinted from [13] Copyright with permission from Elsevier

methylenediphenyl-diisocyanate (PMDI) increases the ductility and improves the interfacial interaction between the fibers and the matrix, thereby improving the stress transfer between them. This in turn is displayed in the increased tensile strength of the composite material. The schematic representation of the compatibilization mechanism of PMDI is shown in Fig. 11. Flexural properties of the composites also showed an improvement on addition of PMDI compatibilizer. Biocarbon-PTT composites reported by Mohanty and co-workers showed a 60 and 14% improvement in flexural modulus and flexural strength compared to neat PTT matrix [36]. However, the ductility of the material decreased as implied by reduction in yield elongation and impact strength. It can be seen that most of the properties of the prepared materials are on a comparable level to the commercial thermoplastic, making it a potential candidate for highly sustainable and light weight engineering applications. When biocarbons derived from peanut hull and miscanthus were used as a reinforcements, a reduction in mechanical properties like the tensile strength and

Fig. 11 Schematic representation of PMDI compatibilization mechanism [50]

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flexural strength were observed which was attributed to poor layer adhesion, larger size of the particles and agglomeration of particles [37, 48]. The effect of size on the mechanical performance of the composites was investigated in detail by Nagarajan et al. [37]. Particles in the optimum size range of 20–75 µm showed a significant increase in impact strength due to their better dispersion in the polymer matrix.

3.1.5

Morphology

Morphological studies help us in getting a better understanding of the mechanical and thermal behavior of polymer composites. Fracture surface morphology of PTT-glass fiber composites showed that the fiber is uniformly dispersed in the matrix and they have a high degree of orientation which is reflected in their high fiber efficiency factor, which in turn shows in their higher mechanical strength (Fig. 12). The glass fibers treated with polypropylene-grafted maleic anhydride (PP-g-MA) possibly react with PTT resulting in a strong interaction between the fiber and the matrix. This may be the reason for the improved tensile and impact strength of the composites [30]. Similar results were observed in the case of short glass fiber reinforced PTT composites reported by Run et al. [53]. Short glass fibers treated with a silane coupling agent showed strong adherence to the resin. This can be seen from the SEM images of the composite showing SGF surface enwrapped with PTT resins. The strong interaction between the fiber and the matrix may be the reason for the improved mechanical properties of the composites. SEM micrographs of carbon fiber-PTT composites showed more agglomeration and lower degree of fiber orientation at higher fiber loadings which resulted in lower efficiency factor [68]. PTT reinforced with biocarbon from peanut hulls also showed agglomeration at higher concentrations [48] (Fig. 13).

Fig. 12 FESEM micrographs of the fracture surface of glass fiber-reinforced PTT composites a 30% glass fiber-reinforced PTT composites, and b 40% glass fiber-reinforced PTT composites. Reprinted with permission from [30]. Copyright American Chemical Society

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Fig. 13 SEM images of a neat PTT and b 80wt.% PTT with 20 wt.% peanut hull biocarbon [48]

Recycled carbon fibers showed more promising results compared to virgin carbon fiber at all fiber concentrations. This may be due to activation of fiber surface during the recycling process [20] Biocarbon reinforced composites of PTT showed sizedependent morphology. Better morphology was observed in the case of 20–75 µm particles which shows that they have better dispersion. Use of chain extenders resulted in much finer morphologies with dispersed small polymer particles. Substantial improvement was observed in the case of impact strength of the composites that possessed such morphologies which favors high energy dissipation mechanisms [37]. Cellulose-based reinforcements showed lesser interactions with the PTT matrix which can be inferred from the SEM images which show a gap between the fiber and matrix and longer pull outs of the fiber [13] (Fig. 14).

3.2 Properties of PTT Nanocomposites 3.2.1

Mechanical Properties

Many works are reported in which different varieties of nanoclay are utilized as fillers. Researchers could obtain significant improvement in various properties when compared to neat polymer. Cloisites-93A Clay/PTT composites were synthesized by melt extrusion. Dwivedi et al. could achieve improvement in various parameters like tensile strength, impact strength, tensile modulus, tensile strain, flexural modulus, and flexural strength. The interactions between the PTT matrix and layered clay are supposed to be the reason for this betterment. Deformation or relaxation of the matrix is not considered to be of same extent as the rigidity of the PTT polymer is less than that of organoclay [65]. Greater stretching of the clay along with well dispersion,

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Fig. 14 SEM pictures of PTT: first-line PTT with 30 wt% carbon fiber-, second-line PTT with 30 wt% glass fiber. Reprinted from [13] Copyright with permission from Elsevier

reinforcement, and intercalation may also result in obtaining efficient nanocomposites [8]. There was considerable change in thermal stability and nucleation formation which further resulted in better crystallinity. Biodegradable PTT/lignin/carbon fibers are developed by Gupta et al. by melt extrusion. It is reported that a significant improvement in mechanical properties was achieved for the nanocomposites with 1.5 wt% lignin and 7 wt% vapor grown carbon fibers. When the mechanical properties were examined, an enhancement of 19.9% in tensile strength, 12.19% in tensile modulus and 46.73% in impact strength were obtained. Cost-effectiveness, low energy consumption, biodegradability, renewable nature, and low density were the reasons for the choice of lignin as the filler in this study. Reinforcing ability of lignin is investigated in this work and it was seen that they are viable for end-use applications because desirable properties were obtained by the formation of these nanocomposites [15].

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Morphological Properties

Polymer nanocomposites are considered to be viable substitutes to conventional blends and composite materials. Morphological characteristics are considered as one of the key features determining the chemical, thermal, mechanical, and physical properties. Well dispersion of fillers is the significant factor for the achievement of functional materials. This dispersion can be analyzed by various methods of characterization such as scanning electron microscopy, transmission electron microscopy, and optical polarizing images. Many research groups have studied the effect of numerous types of fillers on the properties. Morphology studies of clay aggregates can be done by scanning electron microscopy. Since scattering densities of PTT and clay are different, morphological studies are very evident from SEM images. PBT/PTT/ organoclay composites were prepared by twin-screw extruder. In this work, ultra-low-density polyethylene grafted glycidyl methacrylate acted as an impact modifier. Morphological studies reveal that 3 wt% organoclay uniformly dispersed in the matrix and well-defined spherulite formation was obtained by optical polarizing microscopy [62]. Run et al. also performed a similar study in which organomontmorillonite is incorporated in PTT/ maleinized poly(octene–ethylene) by melt-blending method. When the morphology studied it was seen that, some of the organomontmorillonite are peeled off which helped in even dispersion of nanosheets in the matrix. As a result, melt viscosity increased with the filler content. So better processing properties may be expected from this nanocomposites. Not only morphological changes, but there was also considerable effect on tensile and impact strength too due to the better interaction of matrix and filler. TEM studies were also used to study the dispersion of the filler in PTT matrix. It gives a qualitative idea of the internal structure of the composite. Paszkiewicz et al. prepared PTT/poly(tetramethylene oxide/ graphene nanoplatelets/single-walled carbon nanotubes hybrid nanocomposites. The uniform distribution of nanofillers is favored by the heterogeneous structure of the matrix. Transmission electron microscopic (TEM) images of the nanocomposites showed that hybrid nanofillers displayed good distribution than individual fillers. The TEM images are also useful in explaining the mechanism behind the enhancement of conductivity. In some images, we can see that there is well dispersion between the two nanofillers, and they are connected to each other [44]. Electrospinning techniques have been used to prepare PTT/graphene nanocomposites and from the SEM images, it is clear that as the quantity of graphene increased, there are irregular structures formed along the fiber. At higher content of nanographene, there is observable nanofibril formation. From TEM images, the filler content is clearly identifiable and nanofiller protrusions are seen from the smooth PTT fiber. These protrusions clearly indicate the nanocomposite formation [19] (Fig. 15).

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Fig. 15 Scanning electron microscope (SEM) and TEM images of electrospun PTT fibers filled with: a, b 1 wt %, c, d 3 wt % nanographene [19]

3.2.3

Rheology

Poly (ethylene terephthalate) (PET)/ PTT/Montemorillonite (MMT) nanocomposites could achieve a better rheological property than neat polymer as these nanocomposites are pseudo-plastic fluids. Intercalated or exfoliated structures are identified by X-ray diffraction. Also, the viscosity of the nanocomposites melts is found to be lower than that of PET/PTT melt, and as a result, their flow behavior is better than that of PET/PTT melt which in turn lowers the processing temperature of nanocomposites [70]. Gurmendi et al. synthesized PTT/montmorillonites hybrids by melt mixing and rheological properties were studied by varying the type and quantity of clay content. It was seen that viscosity decreases with an increase in clay content. Surfactant migration, as well as changes in the structure of the nanocomposites during degradation, are considered as a reason for a decrease in viscosity [16].

4 Conclusions PTT is one of the most common substances involved in engineering thermoplastics. Many aspects concerning PTT, like synthetic methodologies, morphological structure, physical and chemical properties, its blends, and micro and nanoscale composites technology have been studied. Recent research in the realm of PTT

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nanocomposites indicates the application toward commercialization of novel enduse materials. Hybrid micro and nanocomposites consisting of PTT and numerous fillers were synthesized with the aim of assessing the dispersion of fillers and enhancement of various properties. Different methodologies such as in situ polymerization, melt mixing, injection molding, electrospinning, sol–gel technique, and extrusion processes were developed. The thermomechanical properties were reliant on both the type and quantity of fillers in the polymer matrix. Both SEM and TEM analyzes identified the morphologies of the hybrids along with the mode of dispersion. In addition, there was an improvement in mechanical, electrical, thermal, and rheological properties with the incorporation of fillers. In summary, the addition of fillers to PTT was found to affect the tensile, mechanical properties, and thermal behavior of the polymer.

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Chapter 6

Characterization Techniques Used to Study Various Macro and Nanocomposites of PTT P. S. Sari and Arunima Reghunadhan

1 Introduction Functional polymers are an important class of materials in the industry as well as in research. The reactive groups which are present in these types of polymers offer a wide variety of combination possibilities with other polymers and fillers. Composite fabrication and blending are two major methods employed in the case of polymeric materials in order to make it as a product. Both have their own significance and drawbacks. When considering particularly the functional or reactive polymers, the blending and composite preparation are equally exploited. Polytrimethylene terephthalate is an important member of the family of functional reactive polymers. It has been well known in terms of its properties and applied fields. The applicability of any blend or composite is decided after the analysis of its properties using different characterization techniques. The common procedure includes the characterizations such as thermal, mechanical, scattering, morphological, spectral, permeability, and sorption studies. This chapter is detailing the use of different techniques for the characterization of PTT-based macro, micro, and nano composites.

1.1 Composites of PTT A large contribution toward the PTT-based composites is from carbon nanotube as a filler [1–4]. These composites are showing electromagnetic interference shielding P. S. Sari Department of Polymer Science and Rubber Technology, CUSAT, Kochi, Kerala, India A. Reghunadhan (B) Department of Chemistry, TKM College of Engineering, Karicode, Kerala Kollam-691005, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. R. Ajitha and S. Thomas (eds.), Poly Trimethylene Terephthalate, Materials Horizons: From Nature to Nanomaterials, https://doi.org/10.1007/978-981-19-7303-1_6

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properties in most of the cases. Composites are reported with biopolymers like cellulose and its derivatives [5, 6]. Fillers like carbon black, carbon fibers, graphene sheets, biomaterials, etc. [7–9]. The fillers added to the composites generally influence their properties positively. Most of the aforementioned fillers are added to enhance the thermal, mechanical, and electrical properties of the engineering polymer, PTT. When cellulose is added to the PTT matrix, the resultant micro composite materials show enhancement in mechanical strength. It also influences crystallinity and thermal stability [10]. Other than the polymer-filler composites, there are plenty of blend nanocomposites of PTT. Both compatible and incompatible polymers are explored in these composites. The combination of thermoplastics is more considered due to the favorable conditions in the processing. In the blend nanocomposites, generally, nanofillers are added in order to enhance the miscibility and compatibility. The CNT-based composites are mainly discussed under the blend nanocomposites, where the pi bonds in the pristine CNT and the different groups in the functionalized CNTs act as the link or compatibilizing agent. PTT/PP composites are reported that use MWCNT as the compatibilizing agent showed superior properties [11]. The influence of the second phase polymer and the filler are studied by different methods and are detailed in the coming sections.

2 Characterization of Composites and Nanocomposites of Poly-Trimethylene Terephthalate The characterization techniques most commonly employed are for different purposes. The preliminary idea about the backbone structure and the changes in it are deduced from spectral techniques. The mechanical properties are the next to study to understand the influence of the second phase, and the tensile properties, impact properties, tear tests, flexibility, etc., are the most commonly analyzed properties. Thermal characterization is carried out to understand the thermal stability, degradation, heat dissipation, crystallization, melting, etc. The changes in the morphologies, miscibility, phase separation, filler localization, fibrillation are analyzed using different microscopic techniques and are very relevant inorder to predict the influence of the filler or the second polymer on the matrix material. Specific properties such as conductivity, dielectric strength, viscoelastic properties and.

2.1 Spectral Characterization It is also known as vibrational rotational spectroscopy it is dealing with the vibrational transitions of a molecule. The vibrational spectroscopy gives an idea about the structure of compounds since each functional group in the compound will have a particular vibrational frequency. The addition of foreign material is easily identified

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from FTIR by comparison with the standard spectra. In the case of polymer blends, the mixing or miscibility of the two polymers is identified by the change in intensity and width of the peaks. The change in functional group vibrations by the addition of fillers is also well understood by this technique. Poly trimethylene terephthalate is studied under polyester polymers as its functionality is R-COO-R’. The analysis of the FTIR spectrum of pure PTT, shows one strong peak attributed to its ester group (1711 cm-1), another one at 1465 cm−1 for the bending vibrations of methylene, the band at 1408 cm−1 , represents the C–C stretching vibration in the benzene ring and the bands around 1017 and 723 cm−1 , which is to the bending vibration of the phenylic C-H bonds [12]. Grafted PTT was composited with carbon nanotubes by Braga and fellow researchers and was suggested to be used as antistatic packaging materials. The success of grafting and composite preparation was analyzed by the FT-IR spectral studies [13]. The reactivity is important information obtained from spectral studies. The incorporation of fillers either intensifies or diminish the characteristic peaks of PTT. The effectiveness of grafting between PTT and maleic anhydride (MA) was analyzed using FT-IR. Two shoulder peaks that are characteristic of carboxylic acid anhydride groups were observed at 1,786 and 1,852 cm−1 in the modified PTT-gMA spectrum. The shoulders represent free acid in the modified polymer PTT-g-MA and thus indicate the successful grafting of MA onto PTT (Fig. 2). The spectra also confirmed that there occurs only physical interaction between the filler and the matrix and that the peaks in the silica-modified carbon nanotubes remained less affected [14]. The possible chemical interactions between two polymers in a blend and between a polymer and a filler are well understood from spectral studies. In an interesting report by Sarathchandran et.al, the interaction between PTT and epoxy resin and between PTT and thermally reduced graphene. They have applied theoretical fitting by selecting the ratio of two peaks in the matrix polymer to study the variations in the characteristic absorptions by the addition of a second phase. In addition to the interaction, the mixing ratio, residuation reaction of the functionalities of graphene were studied [15]. Mohanty and coworkers prepared bio PTT nanocomposites with lignin nanoparticles (LNPs) and vapor grown carbon fibers (VGCF) using melt mixing and injection molding. The influence of the nanofiller inclusion on the polymer is well understood from FTIR [16]. The –OH group of LNP and VGCF contributed to the intensification of the peak assigned to the O–H stretching vibration at 3200–3400 cm−1 . The bio-PTT/LNP/VGCF hybrid nanocomposites’ FTIR spectrum revealed a peak at 1708, 2862, and 2934 cm−1 . This peak was assigned to the polymer’s ester carbonyl stretching vibration and C–H stretching vibration. These spectrum results show that the VGCF group in bio-PTT/LNP nanocomposites covalently reacts with the hydroxyl groups of LNP and VGC to form split and cross-linked macromolecules. NMR spectra give information about the environmental changes taking place in the case of magnetic nuclei such as 1 H, 13 C. A handful of information can be obtained from the NMR analysis. Like FTIR, the key application of the NMR technique is to understand the reactions between the components in a composite. When PTT is

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involved in the composite formation, there is a chance for the trans esterification reaction. Such a reaction was followed by NMR spectra of PTT grafted with acrylic acid (AA) and composite with MWCNT. The 13 C NMR spectra revealed that in comparison with neat PTT, the spectrum of PTT-g-AA contained three additional peaks: δ = 35.6 ppm, δ = 42.2 ppm, and δ = 175.1 ppm. These peaks confirmed the grafting ofAA onto PTT. The 13 C NMR spectrum of the PTT/MWNT) exhibited peaks not observed in neat PTT, corresponding to aromatic carbon atoms in the MWNT (δ = 120–125 ppm). Peaks originating from the reaction between –COOH in PTT–g–AA and –OH in MWNT–OH were found at δ = 177.1 ppm and δ = 178.7. [17] The transesterification reaction between phenoxy and PTT was also clarified and explained using 1 H NMR spectra. The changes in the trans reaction by the addition of clay particles in the nanocomposites were also well understood from NMR analysis [18]. Figure 3 depicts the formation of polyoligomeric silsesquioxane-modified PTT composites. The NMR spectrum of the POSS-PTT composites justifies the scheme of reaction given in the figure. The isobutyl moieties of POSS units show three peaks at δ = 0.70 ppm corresponding to Si-CH2 , δ = 1.04 ppm owed to CH–(CH3 )2 , δ = 1.95 ppm (–Si–CH2 –CH). The peak corresponding to the methylene protons of PTT segments was observed at dδ = 2.46 ppm (O–CH2 -CH2 ) and δ = 4.7 ppm (–O–CH2 ). Hence, from the results of FTIR and 1H NMR of purified PTT–POSS nanocomposites, one can confirm the chemical structure of PTT–POSS nanocomposites as in the schematic. NMR spectra were also used to find out the weight fraction and mole fraction of the filler in the composite. The following equation was found helpful for the calculation [19]. Mole fraction of POSS =

A1.04ppm /42 ( A1.04 /42) + ((A2.46ppm + A4.7ppm )/6)

The next spectroscopic technique which is useful in the characterization of PTT composites is Raman spectroscopy. It is applicable in composites when the filler is carbon-containing such as CNTs, modified CNTs, carbon fibers, graphene oxide, and their derivatives [20]. The dispersion of nanofiller in the polymer matrix is understood from the spectra. The characteristic bands in Raman spectrum of PTT appear as follows: The 909 cm−1 bands, assigned to the stretching of the three methylene groups of the glycol residue; small peak at 937 cm−1 assigned to the band of the vibration of the crystalline glycol residue, 1116 cm−1 band assigned to the crystalline phase gauche conformers, the 1612 cm−1 and 1714 cm−1 bands associated with C = O stretching, 3077 cm−1 assigned to C-H stretching. In comparison with the spectrum of CNTs or graphene, there was an increase in the intensity of peaks in the composites which confirm the inclusion of filler in PTT matrix [3, 21, 22].

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2.2 Morphological Characterization of PTT Composites Morphological analysis is an inevitable technique for any blend or composite. The changes in the morphology give significant information regarding miscibility, phase separation, compatibilization, crystallinity, etc. The morphology can be related to mechanical and other properties. The establishment of morphology-property correlation is an important factor in the study of composites. Mohanty et.al, in their study of PTT/carbon fiber composites the microscopy analysis revealed the absence of agglomeration and finer dispersion of the fibers. This fineness in dispersion enhanced the tensile properties [23]. In the case of nanocomposites, the transmission electron microscopic analysis plays a key role in the prediction of properties. Using optical microscopy, it is convenient to study the crystallization studies of PTT composites and nanocomposites. Binary and ternary blend nanocomposites are widely studied for understanding the influence of filler on crystallization [24]. When the clay was added as the filler in PTT matrix, it will affect its crystallization. The crystalline segments in the PTT are exhibited as spherulites when observed through a microscope. The spherulitic growth is often influenced by the addition of the nanofiller. The layered structure of the clay is the reason behind the influence on the crystallinity of PTT. The nucleation agents are the clay layers. A large number of nuclei created by nucleation agents develop in a limited region at the same time, resulting in the creation of tiny spherulites [25] (Fig. 4). PTT shows a standard spherulite picture with no banding morphology. The nanocomposites, on the other hand, have a very distinct morphology [26]. In general, the occurrence of banded spherulites in PTT is greatly influenced by crystallization temperature (Tc). The banded morphology fades at lower Tc (195 °C), and a typical spherulite picture forms. Temperatures over 195 °C will result in the production of banded spherulites. Additionally, when silica loading increases, the spherulite size decreases progressively, indicating that silica has a heterogeneous nucleating action. The non-isothermal crystallization studies of PTT-clay nanocomposites are studied by a number of researchers [27–32]. Crystallization studies are theoretically carried out using different models and among them, the Avrami equation was explored much. This equation explains the mechanism of crystallization in semi-crystalline polymer nanocomposites. Many fillers were tested with PTT such as nanotubes, inorganic fillers like calcium carbonate, barium sulfate, silica, and titania. When CaCO3 was used, it made the molecular chains easy to crystalline. On progressing the isothermal studies, second and third melting endotherms were obtained, and the melting temperature decreased with an increase in the amount of CaCO3 [33]. The inclusion of BaSO4 as a filler in the PTT matrix significantly enhanced the crystallinity and crystallization rate of nanocomposites. The highest augmentation of crystallization rate for nanocomposites was seen in nanocomposites containing around 12 wt percent BaSO4 with a range of 2–16 wt percent, as validated by both the Avrami crystallization rate parameter and the Ozawa crystallization rate parameter. The nanocomposites’ Avrami and Ozawa mechanism exponents, n and m,

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were greater than those of pure PTT, indicating a more intricate interaction between molecular chains and nanoparticles that resulted in alterations in nucleation mode and crystal growth dimension. The effective activation energy computed using the Friedman formula decreased as the nano-BaSO4 concentration grew, implying that the nano-BaSO4 made the PTT molecular chains simpler to crystallize during the nonisothermal crystallization process [34]. In another article, the melt mixing approach was used to create PTT/TiO2 nanocomposites with untreated and surface-treated TiO2 . The nucleation efficiency of TiO2 nanoparticles was investigated using the Avrami model and Mo’s approach. It was discovered that the PTT matrix containing surface-treated TiO2 particles had a higher crystallization temperature and melting point than the PTT matrix containing untreated TiO2 particles. Surface-treated TiO2 particles, as opposed to untreated TiO2 , had a lower influence on the degree of crystallization of the PTT matrix, according to the models. The TiO2 nanoparticles operate as a nucleating agent in the PTT matrix, lowering the crystallization time and allowing the polymer to crystallize more easily [35]. Transmission electron microscopic images are clarifying the insertion of fillers in the PTT and how it affects the properties. In the analysis of PTT composites with carbon nanotubes and exfoliated graphene (EG), from the micrograph, more or less transparent graphene platelets have been observed, which confirmed a high degree of exfoliation of EG in a matrix. SEM micrographs of fracture surfaces of PTT nanocomposites with nanotubes. As is generally known, CNTs often tend to bundle together by Van der Waals interaction between the individual nanotubes with high aspect ratio and large surface area and lead to some agglomerations, which prevent efficient load transfer from matrix to a nanotube [36] (Fig. 5).

2.3 Thermal Characterization Extensive research has been performed to investigate PTT composite’s thermal as well as crystallization behaviors using DSC, TGA, and DMA. Differential scanning calorimetry has been widely applied in the investigation of numerous phenomena occurring during the thermal heating of polymer composites, involving glass transition (Tg), melting, crystallization, and curing. The addition of fillers generally increases the thermal stability of the polymer matrix. Being a semi-crystalline polymer, the incorporation of nano or micro fillers into PTT alters the crystallization process of PTT in two ways. One is the positive effect by which the crystallization temperature and rate are increased, because of the nucleating effect of the additives. The other one, the additives hinder the migration and diffusion of polymer molecular chains to the surface of the nucleus in the composites, which resulted in decreased crystallization temperature, a negative effect on crystallization. Most of the fillers, nano to macro act as nucleating agents at lower loading in the crystallization process of PTT. Fibers such as glass fiber, carbon fiber, and steel fibers were used to reinforce PTT and they enhanced the crystallization process at lower concentrations due to the

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nucleation effect, and at higher loadings, the rate of crystallization decreased due to hindering mechanism. Liu et al. reported that the addition of glass fiber into PTT increases the rate of crystallization up to 15% of filler loading. PTT normally has two melting peaks at 230 °C and 217.5 °C as shown in Fig. 1, which corresponds to lamellar with two different thicknesses formed during PTT crystallization. The 230 °C melting temperature of PTT decreased following the addition of glass fiber because the glass fiber acts as an impurity and depresses the melting point. The melting point at 217.5 °C was increased with 15% glass fiber content. Glass fiber lowers the melting temperature due to the role of impurity. Carbon fibers also showed the nucleating effect on PTTs crystallization (37). The addition of 1 vol % stainless steel fibers increased the crystallization temperature of PTT by 27 ˚C [38] (Fig. 6). Carbon nanoparticles, such as carbon nanotubes and graphene are highly effective nucleating agents that can significantly accelerate crystallization kinetics. The influence of clay layers on the crystallization mechanism of PTT was first studied by Liu through isothermal and non-isothermal crystallization methods [25]. Their results

Fig. 1 Chemical structure of PTT

Fig. 2 Schematic diagram of the interactions between PTT, maleic anhydride, and SiO2 in a composite and the resultant changes in the characteristic absorptions (adapted with permission from [14])

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Fig. 3 NMR spectrum of POSS-PTT composites and the possible interactions between the filler and the polymer (Reproduced with permission from [19]

Fig. 4 Spherulitic growth pattern of pristine PTT (a) and PTT/clay nanocomposites (b, c, d) (Reproduced with permission from [25])

concluded that the addition of clay changes the crystallization behaviors of PTT and accelerates the crystallization rate of PTT, indicating that clay layers act as nucleation agents. The crystallization temperatures Tc and the Hc values for PTT/SWCNTs + EG nanocomposites are higher than those of neat PTT. The PTT/0.1SWCNTs + 0.1 EG exhibited the highest Tc value (184 °C) from the whole series of the prepared

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Fig. 5 The microscopic images of PTT composites show the inclusion of exfoliated graphene and CNTs. Left up and down TEM images and right up and down are SEM images of CNT and EG composites, respectively (Reproduced with permission from [36])

Fig. 6 DSC curves of glass fiber reinforced PTT composites [39]

nanocomposites. Changes in the crystallization peak width and the heat of crystallization (Hc) are related to the overall crystallization rate and the extent of crystallization, respectively [40] Thermo Gravimetric Analysis Thermal stability of the PTT composites evaluated by TGA by analyzing T5%, T max temperatures for 5% weight loss, and maximum weight loss were taken as the

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Fig. 7 Thermal gravimetric curves for different PTT/SGF composites

specific temperature of the degradation process. Apparently, the T5% and Tmax of the composites are relatively higher than those of the pure PTTresin (about 6–12 °C). The residues of the composites (wt %) at 500 °C are increasing as the SGF content increases and the carbon residue is some extent increased by the SGF. These results indicate that the existence of SGF modified by SCA enhances the thermal stability of the PTT and the composites are surely having good thermalstability (Fig. 7). PTT and its nanocomposites show two degradation steps in air and one in argon atmosphere since the thermal stabilizer (Irganox 1010) has been applied. Moreover, similar observations were made previously in [4] for PTT reinforced with COOH functionalized multi-walled carbon nanotubes. The first step may correspond to the degradation of PTT chains into smaller parts by the initial scissoring of chains’ ends. During the second stage, these small fragments were oxidized into volatile products and the decomposition of some thermostable structures (such as aromatic structures) formed during former degradation processes has been observed. However, herein the presence of SWCNTs does not affect the degradation process of PTT. The temperature of the maximum rate of mass loss (TDTG, peak on DTG curve) was studied, to determine the thermal stability of the PTT/SWCNTs composites in detail. Dynamic Mechanic Analysis Understanding the effect of temperature on dynamic mechanical properties of PTT and its composites has been characterized using DMA. The storage modulus and loss modulus, and tanδ of the neat PTT and PTT composites containing varying amounts of fillers as a function of temperature were found out. Generally, the storage modulus was increased with the amount of reinforcing fillers and decreased with increasing temperature. In the glassy region, there is a lack of segmental mobility, so the modulus

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of the polymer is always higher. Moreover, the incorporation of nanofillers enhances restriction in chain mobility and thus higher modulus. Inrubbery region (above Tg), the modulus of PTTcomposites is not significantly higher due to an increase in free volume with increasing temperature. The loss factor of a material is related to the energy loss due to energy dissipation as heat under an oscillatory force. The height of the loss modulus peak of PTT/MWCNTcomposites increased at all MWCNT loadings [41]. The increase in height of the E” peak could be attributed to the barrier effect of MWCNTs, which facilitated heat dissipation. The effect of carbon nanotubes on the damping behavior of PTT, i.e., the plot of tan d versus temperature, is shown in Fig. 8. The PTT/MWCNT composites showed an increase in the tan d peak height on the addition of MWCNTs. This indicates the reinforcing effect of MWCNTs in the PTT matrix. Tan d plots were used to calculate Tg [noted as peaktemperature] of PTT/MWCNT composites. From Fig. 8, it can be seen that Tg remains almost unchanged upon the incorporation of MWCNTs into the PTT matrix, probably indicating that fewer constraints from one-dimensional (1D). CNTs nanofiller are imposed on the polymer chains. This is different from the case usually reported in 2D-layered silicate (e.g., clay)-reinforced polymer composites, where the mobility of polymer chains is greatly constricted by the confinement effect from 2D nanoclay platelets, thus usually increasing the Tg of composites. There is no significant enhancement in storage modulus of the composites near the glass transition temperature, also indicating that the addition of CNTs did not hinder significantly chain mobility of PTT and thus no increase in Tg.

Fig. 8 Impact strength of PTT/rCF composites

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2.4 Electrical Properties of PTT Composites The electrical properties of polymer composites are important in high-conductivity applications such as electrostatic discharge devices, electromagnetic interference (EMI) shielding materials, sensors, electrical switching, and electrodes. The electrical conductivity of PTT could be enhanced by incorporating nanofillers like CNT and GNS that are composed of sp2-bonded carbon atoms. Being an insulating polymer, PTT exhibits a conductivity of 10−14 S/cm (at 0.1 Hz), which can increase by 10 orders of magnitude with the incorporation of MWCNT by, approaching a value of 10−3 S/cm for PTT/0.3 MWCNT [42]. Carbon-based nanocomposite materials exhibit a nonlinear increase of the electrical conductivity as a function of the filler content at a certain amount of filler loading, known as the percolation threshold. Several factors affect the electrical conductivity and the percolation threshold of nanocomposites such as the filler’s concentration, processing method, the presence of functional groups and aspect ratio of nanofillers, and distribution in the matrix. Li et al. reported that the electrical volume resistivities of PTT EG nanocomposites declined dramatically at the EG content between 3.0and 5.0 wt % [43]. The electrical percolationthreshold for (PTT) nanocompositesfilledwithSWCNT, MWCNT, and COOH functionalized multi-walled carbon nanotubes was observed at the loading of 0.05 wt% [44], 0.1 wt% [42], and 0.35 wt % [45], respectively.

2.5 Barrier Properties of PTT Composites Pure PTT itself shows adequate barrier properties due to the semicrystalline nature even though it is used in packaging applications. Therefore only very few studies have been reported on the permeability of PTT composites that also give information regarding the dispersion of fillers, especially nanofillers. The nanofillers such as exfoliated graphene and nanoclays create tortoise paths for the gas molecules if they are well dispersed in the polymer matrix. In a study of PTT expanded graphite nanocomposites, the lowest permeability to CO2 and O2 was found to be for the lowest concentration, i.e., 0.05% and largest flake size, i.e., 500 µm of nanofillers [46].

2.6 Mechanical Properties PTT offers several advantageous properties, including good tensile strength, resilience, and outstanding elastic recovery; however, its main disadvantage is poor impact strength. Being an engineering plastic, mechanical characterization for

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example tensile properties, flexural properties, the impact strength of PTT composites is inevitable. This section covers the effect of various fillers such as glass fiber, carbon fiber, steel fiber, and nanofillers on the mechanical properties of PTT. Fibers are usually incorporated into the polymer matrix to enhance tensile strength and modulus likewise PTT/carbon fiber composite prepared via injection molding showed an increase in tensile strength and modulus with increasing fiber content [39]. Increasing tensile strength with the fiber loading is attributed to the stiffness of fiber as well as the good adhesion between fibers and the PTT matrix. Similar observations were reported for PTT/GF, PTT/ SGF and PTT/ recycled CF composites [22, 25, 33] and it is summarized in Table. 1. The observed increase in tensile modulus with increasing CF loading indicates the excellent reinforcing behavior of CFs in a PTT matrix. Prediction of a composite’s modulus through theoretical models helps in understanding the effect of fiber reinforcement on the mechanical properties of the composites. Flexural properties of PTT fiber composites showed a similar trend with tensile properties that means a gradual enhancement in flexural strength and modulus with increasing fiber content. The improvement in flexural properties was considered strong evidence for good fiber PTT matrix interactions by which effective stress transfer was possible. PTT composite containing carbon fibers has depicted higher flexural properties compared to glass fiber composites, because of the same reason [37]. Even the incorporation of 30 wt% recycled carbon fiber has given 194% and 539% improvement compared to neat PTT in flexural strength and modulus increased by respectively [48]. The impact strength of the composite materials, which is a measure of resistance against crack growth against sudden loading, is determined by either the Izod impact test or the Charpy impact test on both notched or unnotched samples. Neat PTT has poor impact strength because of its semicrystalline nature. The impact strength of fiber-reinforced polymeric composites is complex because of the role of the fiber and the fiber/matrix interface, in addition to the polymer. At the same time, the reinforcement effect of fibers reduces the crack propagation rate by forcing the cracks to propagate around the fibers thereby resulting in a longer propagation path for the crack. In corporation of glass fiber increased the impact strength of PTT progressively with increasing fiber content because glass fiber reduces the crack propagation rate by forming new stress concentrations [39]. However, for PTT carbon fiber composites lower loading of CF (5% and 10%) have a negative impact, and higher loading of CF (15%, 20%, and 30%) showed a positive impact [23]. Contrarily, recycled CF enhanced the impact properties of biobased PTT as given in Fig. 8. The presence of nanofillers has a different scenario in the PTT matrix as it shows an optimal filler content below which the mechanical properties of the nanocomposites are increasing and above which the same decreasing. Liu et al. prepared PTT nanocomposites with three types of nano clay and found optimal organoclay contents for tensile strength of the nanocomposites and the optimal contents are 2, 2, and 3 wt % for the DK2-MMT, the 18C-MMT, and the 12C-MMT nanocomposites, respectively [49]. In the case of MWNTnanocomposites, the optimum level of nanofiller

124 Table 1 Improvement in mechanical properties of PTT fiber composites

P. S. Sari and A. Reghunadhan Fiber type/Filler content

% increase in TS

% increase in TM

Fiber efficiency factor ξ

Glass fiber (30 wt %)

100

400

0.65

Carbon fiber (30 wt %)

120

600

0.175

Short carbon fiber (10 wt %)

50

Recycled carbon fiber (30 wt %)

150

550

content was 0.3 wt% [50]. The CaCO3 nanocomposites also have both reinforcement and toughening effects on the PTT matrix, in which 2–8% contents of CaCO3 nanoparticles are preferred for improving both the impact strength and the tensile strength [47].

3 Conclusions Polytrimethylene terephthalate is one of the very widely used engineering thermoplastic polymers. Its composites, both micro, and nano, are studied well around the world. The different applications of the composites are fixed after the characterization by different techniques. This chapter briefly discussed the most common characterization methods used in the analysis of PTT composites and nanocomposites. The crystallization behavior is explained based on thermal, microscopic, and theoretical studies. The morphological analysis clarifies the filler inclusion, and thermal characterizations are used for obtaining the details of thermal stability and the kinetics of the crystallization process. Specific applications require permeability, sorption, and dielectric measurements.

References 1. Xu Y, Jia H-B, Piao J-N, Ye S-R, Huang J (2008) Crystallization behavior of poly(trimethylene terephthalate)/multi-walled carbon nanotube composites. J Mater Sci 43(1):417–421 2. Gupta A, Choudhary V (2013) Rheologic and mechanical properties of multiwalled carbon nanotubes-reinforced poly(trimethylene terephthalate) composites. J Mater Sci 48(9):3347– 3356 3. Martín-Fabiani I, García-Gutiérrez M-C, Rueda DR, Linares A, Hernández JJ, Ezquerra TA et al (2013 Jun) Crystallization under one-dimensional confinement in alumina nanopores of

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22. Huang C-L, Wang Y-J, Fan Y-C. (2016 May) Morphological features and crystallization behavior of the conductive composites of poly(trimethylene terephthalate)/graphene nanosheets. J Appl Polym Sci 133(19) 23. Vivekanandhan S, Misra M, Mohanty AK (2012) Thermal, mechanical , and morphological investigation of injection molded poly(trimethylene terephthalate )/carbon fiber composites 24. Jog JP (2006) Crystallisation in polymer nanocomposites. 22(7):797–806 25. Liu Z, Chen K, Yan D (2003) Crystallization, morphology, and dynamic mechanical properties of poly(trimethylene terephthalate)/clay nanocomposites. 39:2359–66 26. Poly(trimethylene terephthalate )/silica nanocomposites prepared by dual in situ polymerization: synthesis, morphology, crystallization behavior and mechanical Chenguang Yao a , b and Guisheng Yang a , c ∗. 2010;(November 2009):492–500 27. Smith L, Vasanthan N. Effect of clay on melt crystallization, crystallization kinetics and spherulitic morphology of poly(trimethylene terephthalate) nanocomposites. Thermochim Acta. 152–62 28. Xue M, Liu Y, Lv K, Han S, Gao S, Yu G (2020) Prominent crystallization promotion effect of montmorillonite on PTT/PC blends with PTT as the continuous phase. Vol. 12, Polymers 29. Khan AN, Hong P-D, Chuang W-T, Shih K-S (2010) Crystallization kinetics and structure of poly(trimethylene terepthalate)/monolayer nano-mica nanocomposites. Mater Chem Phys 119(1):93–99 30. Ou C-F (2003 Nov) Crystallization behavior and thermal stability of poly(trimethylene terephthalate)/clay nanocomposites. J Polym Sci Part B Polym Phys 41(22):2902–2910 31. Favaro MM, Rego BT, Branciforti MC, Bretas RES (2010 Jan) Study of the quiescent and shear-induced crystallization kinetics of intercalated PTT/MMT nanocomposites. J Polym Sci Part B Polym Phys 48(2):113–127 32. Hu X, Lesser AJ (2004 Mar) Non-Isothermal Crystallization of Poly(trimethylene terephthalate) (PTT)/Clay Nanocomposites. Macromol Chem Phys 205(5):574–580 33. Run M, Yao C, Wang Y, Gao J (2007 Nov) Isothermal crystallization kinetics and melting behaviors of nanocomposites of poly(trimethylene terephthalate) filled with nano-CaCO3. J Appl Polym Sci 106(3):1557–1567 34. Wang Y, Liu W, Zhang H (2009) The morphology and non-isothermal crystallization characteristics of poly(trimethylene terephthalate)/BaSO4 nanocomposites prepared by in situ polycondensation. Polym Test 28(4):402–411 35. Ramesh V, Mohanty S, Panda BP, Nayak SK (2013 Feb) Nucleation effect of surface treated TiO2 on Poly(trimethylene terephthalate) (PTT) nanocomposites. J Appl Polym Sci 127(3):1909–1920 36. Paszkiewicz S, Pawelec I, Szymczyk A (2016 February) Mechanical and thermal properties of hybrid nanocomposites prepared by in situ polymerization 37. Singaravelu Vivekanandhan, Manjusri Misra AKM (2012) Thermal, mechanical, and morphological investigation of injection molded poly(trimethylene terephthalate)/carbon fiber composites. Polym Polym Compos. 16(2):101–13 38. Yao C, Xie T, Yang G. (2008) Melting behaviors, isothermal crystallization kinetics , and morphology of poly(trimethylene terephthalate )/stainless steel fiber composites 39. Liu W, Mohanty AK, Drzal LT, Misra M, Kurian JV, Miller RW et al (2005) Injection molded glass fiber reinforced poly(trimethylene terephthalate) composites: Fabrication and properties evaluation. Ind Eng Chem Res 44(4):857–862 40. Paszkiewicz S, Szymczyk A, Livanov K, Wagner HD, Rosłaniec Z (2015) Enhanced thermal and mechanical properties of poly(Trimethylene terephthalate-block-poly(tetramethylene oxide) segmented copolymer based hybrid nanocomposites prepared by in situ polymerization via synergy effect between SWCNTs and graphene nanoplatelets. Express Polym Lett 9(6):509–524 41. Gupta A, Choudhary V (2014) Effect of multi-walled carbon nanotubes on mechanical and rheological properties of poly(trimethylene terephthalate). J Mater Sci 49(10):3839–3846

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42. Paszkiewicz S, Szymczyk A, Janowska I, Jedrzejewski R, Linares A, Ezquerra TA et al (2017) Comparative study on the properties of poly(trimethylene terephthalate) -based nanocomposites containing multi-walled carbon (MWCNT) and tungsten disulfide (INT-WS2) nanotubes. Polym Adv Technol 28(6):645–657 43. Li M, Jeong YG (2011) Preparation and characterization of high-performance poly(trimethylene terephthalate) nanocomposites reinforced with exfoliated graphite. Macromol Mater Eng 296(2):159–167 44. Paszkiewicz S, Szymczyk A, Sui XM, Wagner HD, Linares A, Cirera A et al (2017) Electrical conductivity and transparency of polymer hybrid nanocomposites based on poly(trimethylene terephthalate) containing single walled carbon nanotubes and expanded graphite. J Appl Polym Sci 134(1):1–9 45. Szymczyk A, Roslaniec Z, Zenker M, García-Gutiérrez MC, Hernández JJ, Rueda DR et al (2011) Preparation and characterization of nanocomposites based on COOH functionalized multi-walled carbon nanotubes and on poly(trimethylene terephthalate). Express Polym Lett 5(11):977–995 46. electrical and barrier properties of graphene PTT.pdf. 47. Wang J, Wang C, Run M (2013) Study on morphology, rheology, and mechanical properties of poly(trimethylene terephthalate)/CaCO3 nanocomposites. Int J Polym Sci 48. Jacob S, Misra M, Mohanty AK (2012) Novel biocomposites from poly(trimethylene terephthalate) and recycled carbon fibres. J Mater Sci 47(16):6056–6065 49. Liu Z, Chen K, Yan D (2004) Nanocomposites of poly(trimethylene terephthalate) with various organoclays: Morphology, mechanical and thermal properties. Polym Test 23(3):323–331 50. Chen G-X, Shimizu H (2008 Feb) Multiwalled carbon nanotubes grafted with polyhedral oligomeric silsesquioxane and its dispersion in poly(l-lactide) matrix. Polymer (Guildf) 49(4):943–951

Chapter 7

Crystallization and Solid-State Characterization of Poly(Trimethylene Terephthalate) and Its Nanocomposites Nadarajah Vasanthan

1 Introduction Poly(trimethylene terephthalate) (PTT) has received a great amount of attention in recent years from industry and academia due to its many advantageous properties which include good tensile strength behavior, outstanding elastic recovery, resilience, and processing properties [1–3]. Being made from renewable resources, PTT has the added advantage of alleviating fossil fuel dependency and delivering more sustainable stock materials [4]. PTT fibers have the softness and resiliency of nylon fibers, as well as the stain resistance and chemical stability of their aromatic polyester counterparts, which make PTT more desirable for carpet and textile applications [5, 6]. One such important characteristic of PTT fibers is their atmospheric dispersed dyeing with colorfastness and natural stain resistance where no high temperature, pH adjustment, or carrier dyeing machine is necessary for dyeing. PTT has also been used in optical data processing, nonlinear optics, and the field of optical communications due to its luminous transmittance and high birefringence [7, 8]. The development of composite materials with high strength, high modulus, and low density by incorporating fillers such as silica, short glass fibers, talc, mica, and graphite in the polymer matrix has attracted a great deal of scientific and technological interest [9–11]. It has been shown that larger amounts of macro-sized and microsized fillers are required to see a significant change in the desired physical or mechanical properties. The macro-sized and microsized fillers lack an intense interaction within the polymer matrix due to the limited interfacial area [12–15]. In the past few years, polymer nanomaterials with substantial improvements in the mechanical, thermal, conductive, chemical, optical, electrical, and gas-barrier properties have drawn much attention. Nanosized particles can be three-dimensional (nanogranules, nanocrystals, N. Vasanthan (B) Department of Chemistry and Biochemistry, Long Island University, One University Plaza, Brooklyn, NY 11201, USA e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. R. Ajitha and S. Thomas (eds.), Poly Trimethylene Terephthalate, Materials Horizons: From Nature to Nanomaterials, https://doi.org/10.1007/978-981-19-7303-1_7

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Fig. 1 Chemical structure of PTT

and spherical nanoparticles such as SiO2 and TiO2 ), two-dimensional (clay), and onedimensional (carbon nanotubes). PTT nanocomposites were prepared using various techniques to compete with other commodity polymers such as nylons and other polyesters [16–20]. The recent studies of PTT nanocomposite fabrication and solidstate characterization of PTT and its nanocomposites are reviewed in this chapter.

2 Poly(Trimethylene Terephthalate) Poly(trimethylene terephthalate), (PTT) is an odd-numbered aromatic semicrystalline polyester that has three methylene groups in the glycol unit with a chemical structure shown in Fig. 1. PTT can be compared to the other two familiar “evennumbered” poly(ethylene terephthalate), (PET), and poly(butylene terephthalate), (PBT), with two and four methylenes in the glycol unit, respectively. PTT is synthesized from the polycondensation reaction or transesterification reaction of 1,3-propanediol with terephthalic acid or dimethyl terephthalate, shown in Scheme 1. PTT was first patented in the 1940s, but the high costs of 1,3-propanediol (PDO) production hindered the mass production of PTT [21]. PTT has become a potential competitor to PET and PBT in the textile, packaging, and engineering thermoplastics markets due to the discovery of cost-effective synthesis of PTT [4, 22]. PTT has become commercially available under the trade names of Corterra and Sorona synthesized by Shell Chemicals and DuPont, respectively. Shell developed a low-cost process of chemically producing 1,3-propanediol from ethylene oxide in the 1990s, since then the interest in PTT has dramatically increased [23]. DuPont developed a biochemical process more recently for the production of 1,3-propanediol derived from renewable corn sugar and fossil fuel-derived terephthalic acid [24].

3 PTT Nanocomposites Polymer nanocomposites are believed to overcome the limitations of traditional microcomposites and received great interest in research and industrial laboratories [25–39]. The nanoparticles can be added either to the monomers during polymerization or after polymerization either by blending in the melt or solution. These nanoparticles are usually low in cost, enhance polymer matrix performances, and improve

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Scheme 1 Synthetic scheme of PTT produced by polycondensation of 1,3-propanediol (trimethylene glycol or PDO) with either purified terephthalic acid (PTA) or dimethyl terephthalate (DMT)

adsorption and barrier properties of the polymer due to the high surface area of these fillers. The gain in physical and mechanical properties depends on dispersion and interaction between nanoparticles and polymer matrices. Polymer nanocomposites based on layered silicates (particularly MMT) have received a great deal of attention [25–37]. The clays are generally highly hydrophilic and may cause thermal degradation reactions. They are naturally incompatible with most of the polymers and are modified by organic surfactants to improve compatibility. Based on the interaction between polymer and layered silicates, four types of morphologies were reported. Phase-separated, intercalated, intercalated and flocculated, and exfoliated nanocomposites are shown in Fig. 2. When the individual silicate layers get separated and dispersed randomly in a polymer matrix, exfoliated nanocomposites are formed. The exfoliated nanocomposites are preferred due to the best property improvements. The effect of silicate fillers on the crystal morphology of PTT/clay nanocomposites was studied [31–37]. A series of intercalated PTT-clay nanocomposites was

Phase separated

Intercalated

Intercalated and flocculated

Exfoliated

Fig. 2 Different structures and morphologies of polymer–clay nanocomposites [26]

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prepared using a twin-screw extruder by the melt mixing of PTT with quaternary or ternary ammonium salt-modified clays. It was demonstrated that the clays usually act as nucleating agents during crystallization. PTT nanocomposites were studied by WAXD and TEM and showed that the PTT nanocomposites are intercalated. These PTT nanocomposites showed an increase in the dynamic modulus of PTT and a decrease in the relaxation intensity [31]. Liu et al. prepared three different nanocomposites of PTT via melt blending of PTT and organoclay (DK2TM ) using a co-rotating twin extruder [32, 33]. Thermogravimetric analysis (TGA) showed that the PTT/clay nanocomposites are more thermally stable than the neat PTT. The mechanical properties of all the PTT nanocomposites showed an improvement compared to neat PTT. These nanocomposites were characterized by using WAXD and TEM and showed these nanostructures are exfoliated. Chang et al. prepared organically modified montmorillonite (OMMT) containing PTT nanocomposites by in situ intercalation polymerization [34]. Stress-induced crystallization study of these nanocomposites showed that PTT nanocomposites have both increased thermal and mechanical properties with increasing clay content. It has been shown that the addition of a small amount of organically modified clay is sufficient to improve the thermomechanical properties of PTT hybrid fibers. Further, the ultimate tensile strength was decreased with increasing draw ratio from 1 to 9, whereas the initial modulus remained the same. Clay particles with a size greater than 10 nm were found to agglomerate within the PTT matrix. PTT nanocomposites were prepared with two different clays (Cloisite 15A and Cloisite 30B) more recently and shown that exfoliation depends on the hydrophobicity of the clay. PTT nanocomposites with Cloisite 15A formed fully exfoliated composite, whereas PTT nanocomposites with Cloisite 30B formed partially exfoliated and intercalated composites [38, 39]. During the past fifteen years, PTT nanocomposites were prepared with other nanoparticles such as carbon nanotubes, graphene nanosheets, silica, ZnO, and mesoporous silica [40–42]. The PTT nanocomposites with varying amount of mesoporous silica, SBA-15, were prepared by in situ polymerization. A decrease in molecular weight was observed with the addition of SBA-15 particles, and it was attributed to the restricted movement of PTT oligomers in the presence of SBA-15 during polymerization. SBA-15 was found to be well-dispersed and formed nanostructured PTT nanocomposites [40]. The decrease in molecular weight didn’t have any effect on melt viscosity. PTT/silica nanocomposites and PTT/ZnO nanocomposites were fabricated by dual in situ polymerization [41, 42]. FTIR and NMR studies confirmed that PTT chains were grafted on silica and ZnO particles, and these nanocomposites were insoluble in typical solvents used for PTT dissolution. Transmission electron microscopy and scanning electron microscopy showed silica particles with a size of 40–50 nm and ZnO particles of a size 20–30 nm were homogeneously dispersed in the PTT matrix. PTT/silica sol–gel nanocomposite was prepared recently via in situ hydrolysis and condensation of precursor tetraethoxysilane (TEOS). The scanning electron microscopy and zeta-sizer results showed that the silica particles with a size range of 80–100 nm were homogeneously dispersed in the PTT matrix [43].

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4 X-ray Diffraction 4.1 PTT X-ray diffraction (XRD) photos and crystallinity of as-quenched, drawn, and drawn and annealed PTT samples are shown in Fig. 3. The quenched PTT film showed a diffuse halo in the XRD pattern, suggesting that the quenched PTT films are almost in the amorphous state [44]. The annealing and drawing increased the crystallinity of PTT and the XRD pattern showed crystalline reflections at the meridian. The crystal structure of PTT has been determined by electron diffraction and XRD, and only one crystal form has been identified as of yet [1, 45–48]. The unit cell of this crystal form is triclinic, with a = 4.637 Å, b = 6.226 Å, c = 18.64 Å, α = 98.4°, β = 93°, and γ = 111.5°, and it has a density of 1.432 g/cm3 . A single chain passes through each unit cell, and two monomer units are present in a unit cell, which allows for the formation of a helical PTT structure. It is known that PET and PBT adopt extended all trans conformation, and they take 97 and 92% of the c-axis length, respectively. It was shown that the ratio of the unit cell c-axis dimension to the extended chain length of PTT is only about 75%, indicating that PTT adopts a more contracted conformation along the c-axis than PET and PBT. PTT molecules are therefore easier to be deformed in the crystals than PET and PBT [3]. Crystal moduli of polymers with helical conformation are usually low compared to all trans conformation. Nakame et al. reported that the crystal modulus of PTT as 2.59 GPa compared to the crystal modulus of 107 GPa for PET [49]. The crystal modulus was found to be temperature-dependent. For example, crystal modulus was 2.59 GPa at 300 K that increased to 5.39 GPa at 18 K along the chain axis [45]. XRD patterns of PTT and PTT nanocomposites appeared to be similar and concluded that PTT is not altered by the incorporation of clay or other nanoparticles such as SiO2 [38–43].

As-quenched

Drawn

Drawn and annealed

Fig. 3 X-ray diffraction photograph of as-quenched, drawn, and drawn and annealed PTT [44]

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5 Thermal Properties 5.1 PTT Thermal properties of PTT such as glass transition temperature (T g ), cold crystallization temperature (T cc ), and melting temperature (T m ) of PTT were obtained by heating the amorphous PTT film. PTT has a T g at 40–55 °C, T cc at 60–70 °C, and T m at 210–230 °C [45, 50–55]. The T g of PTT was reported by Gonzales et al. as 44 °C [55], whereas the T g of PTT was reported by Yaman et al. [54] as 54 °C. It was reported that that the T g and T cc may vary with the molecular weight and crystallinity. Isothermal cold crystallization of PTT was conducted by annealing, and the T g and T cc disappeared completely when crystallization temperature is exceeded 80 °C. Two melting transitions T m 1 and T m 2 were observed for those samples annealed at above 120 °C. Crystallinity values were obtained for PTT films annealed inside the DSC before and after cooling to room temperature and additional crystallinity of 3 wt% developed during cooling to room temperature, attributed to lamella thickening [54]. Vasanthan et al. [56] studied isothermal melt crystallization of PTT by DSC. Triple melting endotherms were observed at the crystallization temperature, T c , below 195 °C, while double melting endotherms were seen at T c , above 195 °C. These multiple melting behaviors were attributed to melting and recrystallization as well as the thermal stability of the crystallites. The equilibrium melting temperature of PTT ranging from 237 to 277 °C was estimated using the Hoffman–Weeks method by several research groups [50, 52–55]. Thermal properties of PTT drawn to different draw ratios at two different strain rates (8.33 × 10−3 and 8.33 × 10−4 s−1 ) at 50 °C were investigated [57]. Three transitions, T g , T cc , and T m , were seen for the amorphous PTT and the films drawn to a draw ratio below 2.5. Both the T cc and crystallization enthalpy decreased with increasing draw ratio and disappeared completely at draw ratios exceeding 2.5 for both strain rates. This observation was attributed to incomplete crystallization during deformation at 50 °C below a draw ratio of 2.5. Table 1 presents the effect of the strain rate and drawing on the T m and T cc , respectively. The T cc shifts to a lower temperature with an increasing draw ratio at both strain rates, suggesting that strain-induced crystallization significantly influences the cold crystallization process. Structural changes during the stretching process have been studied using uniaxially and biaxially drawn PTT films [4]. The stress-induced crystallization has been observed from the stress–strain curve showing an increase of stress at draw ratio 2.5 at which the density was found to increase significantly. A little change in Tg was observed up to draw ratio of 2.5, and an abrupt increase in T g was observed at the above draw ratio of 2.5. The stress-induced crystallization was further confirmed by an increase in and a decrease in crystallization enthalpy [4]. Crystallization kinetics information of semicrystalline polymers is an important step in understanding, predicting, and designing various processing conditions. Isothermal crystallization kinetics of PET, PTT, and PBT was compared by Chuah [1] and Dangseeyun et al. [58] and showed that PTT crystallizes at a rate in between

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Table 1 Thermal properties of drawn PTT as a function of draw ratios and strain rates. All of the data points are averages of at least three determinations [57] Strain rate (s−1 ) 8.33 ×

8.33 ×

10–4

10–3

Draw ratio

Tcc (°C)

Tm (°C)

Crystallinity (%)

1

69

228

12.4

1.5

64

226

16.5

2

55

224

21.8

2.5

48

222

25.2

3

–

221

28.6

3.5

–

221

32.8

1

69

228

21.4

1.5

64

225

21.5

2

60

223

29.2

2.5

55

221

34.6

3

–

221

35.5

3.5

–

220

37.2

rate of crystallization of PET and PBT. The Avrami rate constant of PTT was about an order of magnitude higher than PET and an order of magnitude lower than PBT at the same degree undercooling. Figure 4 shows the reciprocal half-times of crystallization, t1/2 , versus ΔT (Tm –Tc ) for all PET, PTT, and PBT. The kinetics of isothermal melt crystallization of PTT from 200 to 210 °C was studied using DSC [50]. The variation of, half-time of crystallization, t1/2 was plotted against the crystallization temperature and showed that the t1/2 is strongly dependent on crystallization temperature, T c . The t1/2 increased with increasing T c and a discontinuity at 195 °C, suggesting two crystallization processes below and above 195 °C. The isothermal melt crystallization kinetics of PTT was analyzed using the Avrami equation, and the average value of Avrami exponent, n, of 3 was observed for the temperature range studied. Spherulitic morphology with instantaneous nucleation was predicted for melt crystallized PTT. The kinetics of isothermal melt crystallization of PTT with different molecular weights was studied and showed that crystallization kinetics is faster for low-molecular-weight PTT [59]. The non-isothermal cold crystallization kinetics of PTT and subsequent melting behavior were investigated [60]. The Avrami, Tobin, and Ozawa equations were used to describe the kinetics of non-isothermal cold crystallization kinetics. It was shown that both Avrami and Tobin crystallization rate parameters increased with the heating rate, and the Ozawa crystallization rate increased with the temperature. Nonisothermal cold crystallization kinetics of drawn PTT with a different overall molecular orientation has been investigated, and the Avrami equation has been applied to evaluate the kinetic parameters. An increase in the rate constant and a decrease in the Avrami exponent suggested that cold crystallization is faster for a PTT film with a high overall molecular orientation, and a change in growth geometry with orientation was also observed [57].

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Fig. 4 Reciprocal half-time of crystallization t−1 0.5 as a function of the degree of undercooling for PET, PTT, and PBT [58]

5.2 PTT Nanocomposites Thermal properties of a series of intercalated PTT-clay nanocomposites were prepared using a twin-screw extruder by the melt mixing of PTT with ammonium salt-modified clays [31]. It was shown that nanosilicates influence the melting temperatures and the crystallization behavior of PTT. The influence of nanosilicates on the crystallization and melting behavior were distinct up to 3 wt% clay. There was no further change in the crystallization and melting behavior when the clay content exceeded 3 wt%. The heat of fusion of all PTT nanocomposites is 5–11% higher than that of pure PTT which means that the crystallinity of PTT increases with the addition of silicates. Isothermal crystallization kinetics of PTT/DK2 exfoliated nanocomposites was investigated using the Avrami equation and shown clay layers dispersed in the matrix influences the crystallization behavior [32, 33]. PTT/clay nanocomposite films were prepared via a novel two-step approach using two clays, Cloisite 15A and Cloisite 30B. XRD results showed that PTTCloisite 15A nanocomposites were fully exfoliated whereas PTT-30B nanocomposites were partially exfoliated [38, 39]. Non-isothermal cold crystallization temperature and the crystallinity of non-isothermally cold-crystallized PTT-15A nanocomposites increased with increasing 15A content. The crystallinity of isothermally coldcrystallized PTT-15A nanocomposites was shown to increase with crystallization temperature and the clay content, but no clear trend in crystallinity was observed for PTT-Cloisite 30B nanocomposites [39]. Non-isothermal melt crystallization kinetics of neat PTT and PTT-nanocomposites were analyzed using crystallization isotherm.

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Table 2 Kinetic parameters of non-isothermal melt crystallization for neat PTT and various PTT nanocomposites [38] Clay (%) ΔH (J/g) Crystallinity Tc onset (°C) Tc maximum t1/2 (s) n (%) (°C)

Zc (min−n )

0

−53

36

198

189

88.2

3.48 0.2021

1

−56

39

198

188

75.1

3.58 0.2058

2

−57

40

197

189

74.0

3.59 0.2060

5

−59

43

197

190

70.2

3.61 0.2082

10

−61

46

199

195

43.8

3.72 0.2364

The Avrami analysis modified by Jeziorny was successfully used to describe the nonisothermal crystallization kinetics of neat PTT and PTT nanocomposites, shown by the decrease in half-time (t1/2 ) of crystallization and increase in the rate constant (Zc ) as organoclay content increased up to 10% [38] (Table 2).

6 Optical Microscopy 6.1 PTT PTT spherulites during isothermal crystallization were studied using optical microscopy [61–63]. The optical micrographs of PTT melt crystallized at various temperatures were obtained [61]. It was seen that in all cases, nucleation density increased and spherulitic density became finer as T c increased. Elliptical-shaped axialite-like structures were observed at high Tc , and spherulites were apparent at low Tc . It was reported that classical regime I–II and regime II to III transitions occurred at 488 and 468 K, respectively. The banded spherulites were observed for PTT crystallized at temperatures on the borderline of regime II to III transition. PTT was melt crystallized at from 110 to 200 °C obtained by polarized light microscopy by Vasanthan et al. [56] and Yun et al. [62] Optical micrographs of PTT crystallized at 110, 150, and 190 °C are shown in Fig. 5. It shows that the spherulite size increased from about 110 to 120 to 140 µm, respectively [61]. The increase in spherulite size was attributed to a slower crystallization rate at higher crystallization temperatures. Both groups observed banded spherulites for PTT melt crystallized PTT at above 190 °C and periodically arranged concentric rings disturbed above 200 °C [61, 62]. Detailed morphological changes were attributed to the high birefringence of PTT spherulites and the degree of orientation of molecular chains. The degree of orientation of the crystalline lamelle was estimated by image processing of transmission electron microscope (TEM) images and showed that the degree of orientation changed remarkably between the non-banded and banded spherulites.

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Fig. 5 POM micrographs of PTT spherulites crystallized at a 110 °C; b 150 °C; c 190 °C [56]

6.2 PTT Nanocomposites Polarized optical microscopy (POM) is used to study the effect of nanoclay on the morphology of melt crystallized PTT at temperatures from 110 to 190 °C [38]. Figure 6 shows the optical micrographs of melt crystallized neat PTT and PTT nanocomposites with 1, 2, and 5%, Cloisite 15A loadings melt crystallized for 30 min at 150 °C. The size of the spherulites appears to depend on the clay loading of the PTT nanocomposite. The optical micrographs observed for PTT nanocomposites show relatively well-defined spherulitic morphologies with clear Maltese cross-patterns. The spherulite size decreases with increasing clay content from 0 to 5% clay at each melt crystallization temperature. It was also apparent that the smaller spherulites (~30–80 µm) are mixed with larger spherulites (~100 µm) at the lower melt crystallization temperatures, whereas the smaller spherulite size is more consistent, especially at higher loadings of organoclay at higher melt crystallization temperatures. The size of the spherulite is controlled by the amount of crystallinity and the rate of crystallization. These results suggest that the nanoclay particles in the PTT matrix act as seeds for crystallization and enhance the rate of crystallization. The size of the spherulites and clarity of the Maltese cross-pattern of the 10% PTT nanocomposites at all melt crystallized temperatures are less defined compared to that of the 0, 1, 2, and 5% samples. This observation is attributed to the intercalation of the nanoclay particles in PTT nanocomposite only with 10% 15A loading, which is supported by our XRD results. The effect of silica on morphology of PTT/silica nanocomposite fabricated using a novel sol–gel approach melt crystallized at 120, 150, and 180 °C was studied by polarized optical microscopy (POM). PTT shows well-defined nonbanded spherulites, whereas PTT with a small amount of silica (less than 2 wt%) melt crystallized at low temperatures showed banded spherulites. Figure 7 shows a series of POM of PTT and PTT/silica nanocomposites with 0–10 wt% silica melt crystallized at 180 °C for 30 min. POM revealed that the spherulite size gradually decreased with increasing silica loading and increased with crystallization temperature for a given nanocomposite during isothermal melt crystallization [43].

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Fig. 6 POM photographs of 150 °C melt crystallized neat PTT and PTT nanocomposite films with various nanoclay loadings: a neat PTT, b 1%, c 2%, and d 5% [38]

PTT/silica nanocomposites prepared by dual in situ polymerization melt crystallized at 190 °C was studied recently by POM. PTT showed well-defined non-banded spherulites with dark Maltese crosses at lower crystallization temperature (1000), that is, CNTs present a small diameter, in nanometer scale, and length in micrometric scale [46]. Thus, CNT has some difficulties in homogeneous dispersion and adhesion to the polymer matrix. However, some strategies can be used to achieve better dispersion and alignment, together with strong interfacial interactions within the matrix, with the main goal of leading stress transfer across the CNT-polymer interface [46, 47], enhancing some polymer properties, like mechanical and electrical features. Functionalization is a method of surface modification that aims to improve the affinity and to avoid the agglomeration of nanoparticles in a polymer matrix. There are several procedures for functionalization of CNT reported in the literature, for example, covalent and non-covalent functionalization [48–50]. The chemical functionalization with strong acids, such as nitric and/or sulfuric acid, aims at the attachment of oxygenated functional groups, as carboxylic acid, on the MWCNTs surface, which make CNT soluble in many organic solvents [51]. Functionalization is a process that can damage and alter the structure of the CNT. Depending on the process, the CNT surface can become rougher and can occur a shortening of the tubes, as reported by Jun et al. [52] in the treatment of MWCNT using a mixture of concentrated nitric and sulfuric acid followed by oven dry. In this topic, the effects of CNT functionalization on the morphology and the electrical properties of PTT/MWCNT nanocomposites are evaluated.

3.1.1

Effects of CNT Functionalization on the Electrical Properties of PTT

Due to its intrinsic excellent electrical conductivity, CNT is a conducting filler considered an excellent candidate to prepare conducting polymer composites, which can be

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applied in many technological fields, such as electromagnetic interference shielding effectiveness materials (EMI-SE) [53–55] and antistatic packaging [15, 16, 37, 56]. As increase the content of CNT or any other conducting filler in an insulating polymer, the composite undergoes a transition from insulating to conductor material. This behavior is graphically explained in Fig. 2, which illustrates the difference between one-dimensional filler (as CNT) and 3D microfiller (as graphite, carbon black) in achieving the electrical percolation threshold (EPT). EPT is the critical filler content when the electrical conductivity sharply increases, indicating that at this filler concentration, occurred a formation of a conductive network pathway, increasing the electrical conductivity of the nanocomposite several orders of magnitude, compared to the neat polymer. The electrical conductivity increases until saturating with higher fillers content [57]. This is, at low filler content, the particles maintain isolated from each other until a certain value of concentration is reached enough to form a conductive network. At concentrations below the EPT, the electrons cannot travel, being the composite characterized as an insulating material. To achieve a conductive network, the filler concentration must be above the PT [46]. Filler particle concentration, size, shape, and orientation are crucial factors that certainly interfere with the PT [58]. The EPT is dependent on particle diameter: smaller particle size presents low EPT because these particles have a higher possibility to come into contact together [59]. At this point of view, it is interesting to note that some aspects as the amount of filler needed to reach EPT depend on the filler characteristic (shape and size) [60] and fabrication process (which affects filler orientation and distribution on polymer matrix) [61]. The concentration of filler to achieve the EPT in microcomposites, generally is high, about 10–50 wt%, which can

Fig. 2 Schematic representation of the electrical percolation threshold in nano and micro composites: PT can be achieved using less concentration of nanofiller than microfiller (Source Author)

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result in loss of properties, poor mechanical properties, and an increase in composite density [46, 62]. On the other hand, the use of nanofillers, as CNT, requires lower concentration, often low as 0.5 wt% [46], to form a connection pathway, allowing electron flows. The CNT functionalization has a great influence on the electrical conductivity of nanocomposites. The chemical modification leads to the formation of defects on CNTs structures. Particularly, it disrupts the sp2 structure from the nanotube walls. Thus, the electron transport is impaired, interfering in the network pathway [63, 64]. The electrical conductivity of PTT/MWCNT and PTT/f-MWCNT as a function of MWCNT or f-MWCNT (wt%) is shown in Fig. 3. The electrical conductivity of PTT is 1.5 × 10–9 S/m, characterizing as an insulating material. The electrical conductivity increased with the increase of MWCNT content: the addition of 0.5 wt% of MWCNT, the electrical conductivity increased 7 orders of magnitude when compared to neat PTT, reaching 4.9 × 10–2 S/m, indicating the percolation occurrence. With the addition of 1 wt% of MWCNT, the electrical conductivity increased to 4.0 × 10–1 S/m, 8 orders of magnitude. The percolation phenomenon at low MWCNT content can be referred to as the formation of interconnecting network pathways probably due to efficient MWCNT dispersion in the matrix and high aspect ratio [37, 65]. Among many other conductive fillers, as carbon black and graphite, MWCNTs have a higher aspect ratio, thus needing low content to percolate. Huang et al. [66] reported an interesting study to compare the electrical properties of nanocomposites with PTT as a matrix with different fillers: CNT and graphene nanosheets (GNS), and the hybrid GNS-CNT, through simple coagulation. It was used three different types of GNS, prepared from graphene oxide (GO) through hydrazine reduction, and with different aspect ratios and oxygen functional groups: GNS-T (with thermal reduction at 1050 °C), GNS-E (at a higher processing temperature of 1500 °C), and GNS-H (obtained through GO hydrazine reduction). The authors found that the low Fig. 3 Electrical conductivity of PTT/MWCNT and PTT/f-MWCNT as a function of fillers content (Source Author)

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PT reached was for PTT composite with GNS-E (at 0.84 wt%), which has a higher surface area compared to the other fillers. Li and Jeong [67] prepared nanocomposites based on PTT and exfoliated graphite (EG) through melt compounding. The authors found that the electrical resistivity of PTT is about 10+16 Ω cm and decreased significantly in the composite at the EG content between 3 and 5 wt%, indicating that in filler concentration lower than 3 wt%, the nanocomposites presented almost the same value of electrical resistivity as PTT. On the contrary, at filler concentration above 5 wt%, the conduction path is formed, increasing the electrical conductivity, consequently, reducing the electrical resistivity. Paszkiewicz et al. [26] prepared nanocomposites of PTT with exfoliated graphite nanoplatelets (EGN) with two different platelets size: 50 and 500 µm, synthesized by in situ polymerization, and studied the influence of nanoplatelets sizes on electrical properties of the nanocomposite. The electrical conductivity occurred at 0.3–0.5 wt% of the smaller platelet (50 µm) nanocomposite, whereas the nanocomposite with 0.5 wt% of the EGN with platelet size of 500 µm was insulating. SEM images showed that the smaller filler demonstrated a more uniform distribution in the PTT matrix. Besides the filler aspects reported above, chemical functionalization is a process that can interfere in the electrical properties of the nanocomposites. Figure 3 also presents the electrical conductivity of PTT/f-MWCNT nanocomposites as a function of the filler content. The addition of 0.5 wt% of f-MWCNT increased only 2 orders of magnitude (9.7 × 10–7 S/m), and the addition of 1 wt% of f-MWCNT increased 6 orders of magnitude (1.2 × 10–3 S/m). However, the magnitude is not as high as the nanocomposites with non-modified MWCNT (Fig. 3—black line). An explanation for this behavior is that the strong acids, like nitric acid, used during chemical functionalization probably were responsible for destruction on MWCNT walls, which disrupt the interconnected network path and impair the mechanism of electron transport [16, 63, 64]. Paszkiewicz et al. [68] prepared nanocomposites of PTT filled with functionalized MWCNT (MWCNT-COOH) and GNS by in situ polymerization and investigated the addition of different fillers concentration on the electrical conductivity of the nanocomposites. The 1D MWCNT-COOH presents an aspect ratio of 158 and the 2D GNS presents an aspect ratio of 10,000 and a high surface area. The value of the PT for PTT/MWCNT-COOH was 0.35 wt%. The combination of the two types of filler was crucial to enhance the electrical properties: the addition of 1 wt% of GNS into insulating nanocomposite containing 0.2 wt% of MWCNT increased 6 orders of magnitude in electrical conductivity. It is well known that the electrical properties of composites and nanocomposites depend on several parameters as filler size and geometry, and their interaction and dispersion within the polymeric matrix. So, the study of nanocomposite morphology is essential to understand the effects of the filler in the nanocomposite’s properties. The SEM-FEG images permit us to observe the dispersion and distribution of MWCNT in the PTT matrix. Moreover, it is possible to analyze the morphological changes that occurred in PTT/MWCNT nanocomposites after the chemical oxidation of MWCNT, and its interaction within the polymer matrix. Figure 4 shows the

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Fig. 4 SEM-FEG images for PTT_0.5MWCNT (Source Author)

SEM-FEG images of the fractured surface of the nanocomposite with 0.5 wt% of MWCNT (PTT_0.5MWCNT). The micrograph of the nanocomposite suggests that MWCNTs are well embedded in the PTT matrix. Figure 5 shows SEM-FEG images for the nanocomposite with 0.5 wt% of functionalized MWCNT (PTT_0.5 f-MWCNT) where it is possible to observe the fMWCNT dispersed in the PTT matrix, but also some agglomerates of f-MWCNT. In this case, the functionalization of MWCNT was an important factor regarding the good adhesion of the filler within the polymer matrix: it is possible to see that there are no holes in the matrix or empty spaces around the filler. On the other hand, the dispersion was not so efficient, as some regions with agglomerates f-MWCNT could be observed.

3.2 Addition of Compatibilizer Agent The use of a compatibilizer agent in PTT/CNT nanocomposites is a method that can be particularly useful to guarantee a more homogeneous filler dispersion and better interaction in polymer matrix. It acts to reduce the interfacial tension present in polymer blends and nanocomposites [69]. There are mainly two types of compatibilization process, non-reactive and reactive compatibilization. In the non-reactive compatibilization, small amounts of third components, usually block or graft copolymers, are added to the system, in which a part of the compatibilizer can interact or become miscible with one of the polymer components, and the other part with the second component of the mixture. In the case of reactive compatibilization, in situ copolymer formation occurs during processing,

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Fig. 5 a SEM images for PTT_0.5 f-MWCNT and b region showing agglomerates of f-MWCNT (Source Author)

and another important strategy for compatibilization of immiscible blends involves the compatibilization action of micro and nanofillers. The compatibility is capable of using some components that generate functional groups [70]. For example, the use of maleic anhydride (MA) in a polymer permits the increase of surface energy and improvement of hydrophilicity and adhesion with other components as polar polymers and inorganic filler [71]. The compatibilizer agent maleic anhydride grafted PTT (PTT-g-MA) was successfully prepared by Braga et al. by reactive extrusion reaction [69]. PTT/MWCNT and PTT/f-MWCNT nanocomposites were compatibilized with 3 wt% of PTT-g-MA, as described by Braga et al. [69], and the addition of 0.5 and 1 wt% of the MWCNT in electrical properties was evaluated. Figure 6 shows the electrical conductivity of PTT/PTT-g-MA/MWCNT and PTT/PTT-g-MA/f-MWCNT as a function of carbon fillers content. The addition of MWCNT or f-MWCNT increases the electrical conductivity. As the same case as PTT/MWCNT nanocomposites, the functionalization process leads to an increase in the lower order of magnitude compared to the use of pristine MWCNT. However, the addition of a compatibilizer agent to the system did not interfere on the electrical properties of the nanocomposites. Figure 7 shows SEM-FEG images of compatibilized nanocomposites with 1 wt% of MWCNT (a) and f-MWCNT (b). The fracture surface of the nanocomposites containing PTT-g-MA as a compatibilizer agent is characterized by a rough surface. The use of a compatibilizer agent in the PTT/MWCNT nanocomposite is to avoid filler agglomeration and improve filler distribution and dispersion in the polymeric matrix. So, it is possible to verify in Fig. 7b that the MWCNT is well dispersed in the matrix. Even though the functionalization process may cause changes in electric properties, it is an important step to improve the filler dispersion in the matrix.

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Fig. 6 Electrical conductivity of PTT/PTT-g-MA/MWCNT and PTT/PTT-g-MA/f-MWCNT nanocomposites as a function of carbon fillers content (Source Author)

Fig. 7 SEM images a PTT/PTT-g-MA_1MWCNT and b PTT/PTT-g-MA_1f-MWCNT (Source Author)

The preparation of PTT/graphite (GR) composites was also investigated. The influence of the addition of 3 and 10 wt% of GR, 1.5 and 5 wt% of PTT-g-MA on the electrical and morphological properties of PTT/GR composites was verified. The PTT-g-MA was prepared as described by Braga et al. [69]. Figure 8 shows the electrical conductivity values as a function of GR and compatibilizer agent content in PTT/GR composites. It is possible to observe that the addition of 3 wt% GR without a compatibilizer agent did not change the electrical conductivity, as it did not reach the electrical percolation threshold. However, when adding the compatibilizer agent,

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Fig. 8 Electrical conductivity of PTT/GR and PTT/PTT-g-MA/GR composites as a function of graphite and compatibilizer agent content (Source Author)

the conductivity increased by 9 orders of magnitude when compared to the sample without the compatibilizer agent (PTT/3 wt% GR). This fact may be related to the presence of the compatibilizer agent that improved the dispersion of GR in the PTT matrix, as shown in the SEM images from Fig. 9a, b, and consequently facilitated the transport of electrons, influencing the increase in the electrical conductivity. When adding 10 wt% of GR to the PTT matrix without compatibilizer agent, it was observed agglomeration points of GR along the length of the analyzed morphological surface (Fig. 9c), however, an increase of 9 orders of magnitude was noted in the values of conductivity when comparing with PTT/3wt%GR sample. When adding the compatibilizer agent, better dispersion of GR in the PTT matrix was observed (Fig. 9d), however, a decrease of 7 orders of magnitude in the values of electrical conductivity. Thus, even though there was a good dispersion of the filler in the matrix, the large amount of PTT-g-MA (5 wt%) may have acted as an insulator in the composites.

3.3 Addition of Second Phase and Compatibilizer Agent A polymer blend is defined as a physical mixing of two or more polymers, with a minimum concentration of 2 wt% of each component and without a high degree of a chemical reaction between them [72, 73]. Commercial polymer blends offer an appropriate balance of properties with lower cost and shorter development time compared to the creation of new copolymers [74, 75]. So, a widely explored strategy to improve PTT properties is blending it with other polymers, as, PP [76], PE [77], ethylene propylene diene monomer copolymer (EPDM) [78, 79], polycarbonate (PC)

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Fig. 9 SEM micrographs of PTT/3%GR (a), PTT/1.5%PTT-g-MA/3%GR (b), PTT/10%GR (c), and PTT/5%PTT-g-MA/10%GR (d) (Source Author)

[9, 17, 18, 80], and ABS [16, 81, 82], focusing on improving PTT toughness and mechanical performance. General ways to categorize polymer blends are: by their preparation method as solution mixing, molten mixing, and interpenetrating network blends (IPNs); by their mixing behavior as immiscible and miscible blends; and from an application point of view as compatible and incompatible blends [72, 73]. Once PTT is a commercial thermoplastic polymer, the molten process to prepare PTT-based blends and composites is the most attractive considering the production costs and the environmental concern. Additionally, commercial PTT is immiscible with most polymers due to thermodynamical aspects, which include: the chemical similarity between them, the polymer’s chains molecular weight, and crystallinity degree (X c ) [72, 83, 84]. Immiscible polymer blends generally exhibit a weak interface and consequently poor mechanical properties. For these cases, the addition of a compatibilizer agent is generally recommended [72, 73]. The compatibilizer agent addition aims to reduce

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Fig. 10 Scheme of morphologies of a an immiscible polymer blend of PTT and a generic polymer immiscible in PTT, b the same blend with a polymeric compatibilizer agent, and c filler acting as a compatibilizer agent on PTT/polymer blend (Source Author)

the interfacial tension between the two polymers controlling the morphology, distribution, and dispersion of the polymer blend [85]. It also could promote better adhesion between phases, promoting an adequate load transfer of the polymers and fillers of the blend for nanocomposites [72]. As discussed in the previous section, the compatibilizer agent could be nonreactive and reactive, like reactive copolymers as PP-g-MA for PTT/PP blend. Some examples of non-reactive are block copolymers and fillers, such as random PTT-bPC formed by transesterification in PTT/PC blends [9, 17, 18, 80] and MWCNTs for PTT/PP blends [12]. For both cases, the main goal of a compatibilizer agent in polymer blends is controlling and tunneling the blends matrixes’ morphology; also to improve the interfacial strength between the phases [72, 73]. The filler could also act as a compatibilizer agent, reducing the dispersion phase domain sizes and dispersion in polymer immiscible blend-based nanocomposites. Some studies in this direction show this effect for MWCNTs [13] on PTT/PP blends and organically modified montmorillonites on PTT/PP [86, 87] and PTT/PE [77]. Figure 10 represents the effect of a compatibilizer agent on an immiscible blend morphology. Composites developed with an immiscible polymer blend as a matrix, by the selective distribution phenomena, might provide some advantages compared to singlephase polymer composites. Some of those advantages include a higher electrical performance with less filler content, better electromagnetic shielding, and mechanical performance [13, 84, 88, 89]. The selective localization distribution phenomena appear when the nanofillers are preferentially located at one polymer phase or the interface in an immiscible polymer blend [13, 90, 91]. The electrical, rheological, and mechanical properties of nanocomposites with selective localization depend on the double percolation threshold described by Sumita et al. in 1991 [90], where the formation of a percolation threshold is related to the physical continuity of the phase where the filler is located and the percolation content of the filler [90]. Figure 11 schematically exemplifies the double percolation effect in the function of the blend ratio for a PTT and generic polymer blend with selective localization of filler in the PTT phase. The selective distribution and double percolation phenomenon are being studied, aiming to reduce the filler’s content to achieve the best properties improving

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Fig. 11 Schematic representation of possible morphologies of PTT blends composites with the filler selectively distributed the PTT immiscible blend with selective localization of filler in PTT phase, for different blend ratios (Source Author)

nanocomposites morphology. However, understanding the morphology development of these materials is a complex subject; in the literature, there are excellent books about this topic [84, 92, 93]. Therefore, here we focus on a brief review of the morphology development theory, how it affects the composites’ properties, and some discussion about works related to PTT-based blend composites. The morphology of blend-based composites is dependent on thermodynamics and kinetic factors. From the thermodynamic point of view, the surficial tension between the polymers and each polymer with the filler plays a vital role in morphology development, where high surface energy nanoparticles might be preferentially localized at the higher surface energy phase to reduce the total interfacial tension [12], for PTT composites, that relationship could be described by the wetting parameter of Young’s equation [13, 90, 91] (Eq. 1): ωa =

γfiller-Polymer − γfiller-PTT γPolymer-PTT

(1)

In this equation, the γ represents the interfacial tension parameter of two subscribed phases; For example, γ Polymer-PTT represents the interfacial tension between PTT and the other polymer in the polymer blend. The ωa is the wetting parameter of the composite polymer blend matrix for a thermodynamic equilibrium condition. For example, if ωPTT-Polymer is greater than 1, the filler may preferably be localized in the PTT domains; for values between 1 and −1, the filler can be located at both phases and the interfacial region; and for lower values, the filler may

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Fig. 12 Values of wettability parameter (ωa ) and its relationship with the morphology (Source author)

be at the second phase domains (Fig. 12) [13, 90, 91]. Nevertheless, some polymers and processing conditions applied to produce PTT blend base composites might not provide the circumstances for achieving the thermodynamic equilibrium, being the morphology influenced by kinetic factors. Some, important kinetic factors in determining the filler localization are: mixing time, blending protocol, blend viscosity ratio, and filler geometry [9, 94–97]. The mixing time correlates with all kinetic parameters. On the one hand, taking the necessary time to achieve thermodynamic equilibrium, shorter mixing times will lead to the predominant influence of kinetic parameters [94]. On the other hand, however, longer mixing times can lead to polymer chain breaking. The blending protocol defines the order of component addition along the process. Hence, it is possible to develop blending strategies to define which phase might contact the filler during the incorporation step [84, 94]. For example, if the second polymer phase has a melting temperature lower than PTT, in a one-step extrusion processing, the fillers would be better incorporated in that polymer, and the migration to PTT might not occur even if PTT was the equilibrium phase (ωa > 1) [84]. The viscosity ratio between the blend disperse phase and the blend matrix phase defines the blend morphology. The filler migration would be difficult if those viscosities are too different [33, 34]. However, some studies point in a different direction [98–100]. The exact influence is not a consensus in literature yet [74]. The filler’s superficial area, geometry, and dimension also have an expressive effect on their migration. Fillers with a high aspect ratio, as MWCNT, tend to migrate easily to the equilibrium phase [95, 101]. Göldel et al. [101] had described the Slim-Fast Mechanism, in which smaller and thinner particles with higher surface area tend to migrate faster to the equilibrium phase [101]. The following sections discuss some works in the literature applying these general concepts applied to PTT immiscible blend-based nanocomposites.

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Nanoclay PTT Blend-Based Nanocomposites

Xue and Li [86] prepared PTT/PP blend-based nanocomposites by melt mixing with an organically modified montmorillonite commercially named Cloisite® 25A. The authors evaluated the morphological effects of adding this filler and PP-g-MA as a compatibilizer agent in different PTT/PP blend ratios (80/20, 70/30, 60/40, 40/60, 30/70, 20/80). The nanoclay is preferentially located at the PTT phase, and the interface and its addition in PTT/PP blends (80/20 and 70/30) resulted in a refinement of the disperse phase. On the other hand, when PP is the matrix, PTT/PP 30/70 and 80/20 blends, the opposite effect, being nanoclay not a good compatibilizer agent for those blends [86]. Moreover, the addition of PP-g-MA 5 wt% had a positive effect on those nanocomposites morphology, decreasing the size in the disperse phase of the blend, increased the interfacial strength between the blend components, and promoting a better dispersion with an exfoliated structure for the nanoclay. All those results pointed toward advantages in using both components together [86]. Khonakdar et al. [87] had conducted a detailed study of nanoclay filling PP/PTT blends, preparing the nanocomposites by melt mixing in a co-rotational twin screw extruder. Two different nanoclays (Cloisite® 30B and Cloisite® 20A) and n-butyl acrylate glycidyl methacrylate ethylene terpolymer as a compatibilizer agent were applied to prepare these nanocomposites. The affinity of both nanoclays for the PTT phase in PP/PTT was confirmed by TEM for nanocomposites, without compatibilizer, agreeing with the ωa . However, the compatibilizer agent addition resulted in nanoclay tactoids formations in the PP matrix, structures formed by stacks of intercalated fillers, like agglomerates. The effects of the selectively localized nanoclay particles restricting the PTT dispersed phase mobility and the tactoids were seen in the oscillatory rheological properties of these nanocomposites. Similar results were found for different PTT polyolefins blends. Nayak and Mohant [77] studied PTT/linear low-density polyethylene (LLDPE) (70/30) or maleic anhydride grafted LLDPE (LLDPE-g-MA) blend-based nanoclay nanocomposites. In those melt mixed nanocomposites, the nanoclays were preferentially located at the PTT phase and reduced the LLDPE domain sizes.

3.3.2

Carbon Nanotubes PTT Blend-Based Nanocomposites

MWCNTs are promising fillers for PTT blend-based nanocomposites since π-π between PTT chains and the MWCNTs might enhance the movement of electrons [10]. Wu et al. [91] studied the selective localization of CNT in PTT/PC (60/40) blend prepared by melt mixing in an internal mixer. The blend ratio of 60/40 was carefully chosen seeking to balance that immiscible blend morphology, and the symmetry of the transesterification reactions between PTT and PC at the blend interface, forming a random PTT-co-PC polymer that acts as a compatibilizer agent. The authors first prepared blends with and without a catalyzer (Ti(OBu)4 ) and CNT nanocomposites on those blends. Then, the authors proposed a detailed discussion about the CNT location based on the wetting coefficient (ωa ) and some kinetic parameters, as the

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viscosity ratio of the matrix. The catalyzer addition promotes the transesterification reactions reducing the PC dispersed phase size in the matrix. The final morphology observed is the CNT located at the interface and preferentially on the PTT phase, which agrees with ωa calculated and the lower PTT viscosity compared to PC. Moreover, the CNT located at the interface also acted as a catalyst substrate [91], making the CNT a multifunctional filler to that system. MWCNTs can act as a compatibilizer agent for PTT/PP blends, according to Ramachandran et al. [12]. In that study, nanocomposites of PTT/PP/MWCNT were prepared by melt mixing in an internal mixer. As a result, the MWCNTs were selectively located at the PTT phase agreeing with thermodynamic prediction, as observed by TEM images in Fig. 13. Moreover, acted controlling the PP phase size and improved the mechanical properties of PTT/PP blend (90/10) [12]. Ramachandran et al. [10] evaluated PP-g-MA as a compatibilizer agent for PTT/PP immiscible blends and its effect on electrical and electromagnetic PTT/PP/MWCNT nanocomposites. The authors had found that the addition of 5 wt% of PP-g-MA in

Fig. 13 TEM images presenting selective distribution behavior of MWCNT in PTT/PP blends [12]: a 90PTT/10PP/1MWCNT, with phase separation and dispersed MWCNTs in PTT indicated by yellow arrows; b, c, and d present the MWCNT network in 90PTT/10PP/1MWCNT, 90PTT/10PP/2.5MWCNT, and 90PTT/10PP/5MWCNT, respectively. Copyright (2021), with permission from Elsevier

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the PTT/PP/MWCNT (90/10/1) improved the interfacial adhesion and interactions between the components of the nanocomposite. The MWCNTs were dispersed at the PTT phase and the PTT/PP interfaces, resulting in a slight electrical conductivity decrease compared to the nanocomposites without PP-g-MA, with more dispersed MWCNTs weakening the double percolation effect. However, increasing the PPg-MA content to 5 wt%, the author observed a higher EMI-SE, indicating a new strategy to disperse MWCNT on PTT/PP immiscible blends [10]. PTT/ABS blends-based MWCNT was also studied. Figures 14 and 15 show the SEM-FEG from PTT/ABS (80/20) compatibilized with 3 wt% of PTT-g-MA, with 1 wt% of MWCNTs. It is possible to observe the long MWCNTs indicated by the white arrows. Most of MWCNTs were pulled out of the PTT matrix, characterizing weak interfacial adhesion between the filler and the polymeric matrix. Figure 16 shows the SEM-FEG from PTT/ABS (80/20) compatibilized with 3 wt% of PTT-g-MA and 1 wt% of f-MWCNTs. Different from observed in Figs. 14 and 15, in this nanocomposite, the f-MWCNTs seem to be more adhered to the matrix, suggesting strong interfacial interaction, due to the presence of shorter tubes, which were not pulled out, but rather, broken during the fracture. The oxygen-containing groups presented in f-MWCNTs, after chemical functionalization, are responsible for the interaction of the filler with the matrix, which is essential to guarantee the tension transference of MWCNTs to the matrix, increasing the properties of the nanocomposite. Fig. 14 SEM-FEG image of compatibilized PTT/ABS blend with 1 wt% of MWCNTs (Source Author)

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Fig. 15 SEM-FEG image of compatibilized PTT/ABS blend with 1 wt% of MWCNTs and zoomedin image (Source Author)

Fig. 16 SEM-FEG image of compatibilized PTT/ABS (80/20) blend with 1 wt% of f-MWCNTs (Source Author)

4 Conclusions In this chapter, the concept of PTT-based micro and nanocomposites has been reviewed. The effect of the addition of nano and microparticles in the PTT properties was investigated. The electrical conductivity of PTT/carbon nanotubes and PTT/graphite increased with the increase of filler content. However, the PTT/carbon nanotubes reached the electrical percolation threshold at lower filler content (0.5

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wt%) them PTT/graphite, this is because the 1D carbon nanotubes present a higher aspect ratio and surface area compared to 3D graphite. Moreover, to complement PTT-based morphological systems, the addition of a second phase was discussed. Polymer blend-based PTT can be a great alternative to improve PTT toughness and mechanical performance, creating new materials with exceptional properties. Some strategies can use to guarantee homogeneous filler dispersion, as functionalization of the filler and addition of a compatibilizer agent, as PTT-g-MA. Results showed that this approach can improve carbon nanotubes’ dispersion in the PTT matrix, as showed by SEM images. So, the SEM and TEM seem to be great characterization techniques to study the morphology of the blends and nanocomposites, to evaluate the dispersion of the filler within the matrix, and to prove filler/matrix adhesion, being fundamental to understand the system and to correlate to the final properties of the micro or nanocomposite. Acknowledgements This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001. The authors thank FAPESP (process 2020/12501-8) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico, process 310196/2018-3 and 405675/2018-6) for the financial support. The authors also would like to thank the Laboratório Associado de Sensores e Materiais (LAS) from Instituto Nacional de Pesquisas Espaciais (INPE) for SEM-FEG images.

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81. Xue ML, Yu YL, Chuah HH et al (2007) Miscibility and compatibilization of poly(trimethylene terephthalate)/acrylonitrile-butadiene-styrene blends. Eur Polym J 43:3826–3837. https://doi.org/10.1016/j.eurpolymj.2007.06.048 82. Run MT, Wang HS, Li X (2012) Morphology, mechanical, rheological, and thermal properties study on the PTT/ABS/SCF composites. Compos Interfaces 19:333–351. https://doi.org/10. 1080/15685543.2012.728101 83. Utracki AL (1990) Polymer alloys and blends thermodynamics and rheology. J Polym Sci Part C Polym Lett 28:387–387. https://doi.org/10.1002/pol.1990.140281208 84. Thomas S, Shanks R, Chandrasekharakurup S (2014) Nanostructured polymer blends. William Andrew/Elsevier, Kidlington, Oxford 85. Hope MJFPS (1993) Polymer blends and alloys. Springer, Dordrecht 86. Xue M-L, Li P (2009) Phase morphology and clay distribution of poly(trimethylene terephthalate)/polypropylene/montmorillonite nanocomposites. J Appl Polym Sci 113:3883–3890. https://doi.org/10.1002/app.30417 87. Khonakdar HA, Saen P, Nodehi A et al (2013) On rheology-morphology correlation of polypropylene/poly(trimethylene terephthalate) blend nanocomposites. J Appl Polym Sci 127:1054–1060. https://doi.org/10.1002/app.37776 88. Rahaman M (2019) Carbon-containing polymer composites. Springer Singapore, Singapura 89. Thomas S (2018) Advanced materials for electromagnetic shielding. 1:464 90. Sumita M, Sakata K, Asai S et al (1991) Dispersion of fillers and the electrical conductivity of polymer blends filled with carbon black. Polym Bull 1:265–271. https://doi.org/10.1007/ BF00310802 91. Wu D, Sun Y, Lin D et al (2011) Selective localization behavior of carbon nanotubes: effect on transesterification of immiscible polyester blends. Macromol Chem Phys 1700–1709. https:// doi.org/10.1002/macp.201100095 92. Harrats C, Thomas S, Groeninckx G (2006) Micro- and nanostructured multiphase polymer blend systems. Taylor & Francis 93. Ray SS, Salehiyan R (2020) Fundamentals of immiscible polymer blends. Nanostruct Immiscible Polym Blends 1:65–80. https://doi.org/10.1016/b978-0-12-816707-6.00004-3 94. Ray SS, Salehiyan R (2020) Effect of mixing conditions (dynamic process). In: Nanostructured immiscible polymer blends. Elsevier, pp 107–142 95. Ray SS, Salehiyan R (2020) Effects associated with constituents. In: Nanostructured immiscible polymer blends. Elsevier, pp 107–142 96. Sultana SMN, Pawar SP, Kamkar M et al (2019) Tailoring MWCNT dispersion, blend morphology and EMI shielding properties by sequential mixing strategy in immiscible PS/PVDF blends. J Electron Mater 49:1588–1600. https://doi.org/10.1007/s11664-019-073 71-8 97. Rostami A, Masoomi M, Fayazi MJ et al (2015) Role of multiwalled carbon nanotubes (MWCNTs) on rheological, thermal and electrical properties of PC/ABS blend. RSC Adv 5:32880–32890. https://doi.org/10.1039/c5ra04043d 98. Feng J, Chan CM, Li JX (2003) A method to control the dispersion of carbon black in an immiscible polymer blend. Polym Eng Sci 43:1058–1063. https://doi.org/10.1002/pen.10089 99. Plattier J, Benyahia L, Dorget M et al (2015) Viscosity-induced filler localisation in immiscible polymer blends. Polymer (Guildf) 59:260–269. https://doi.org/10.1016/j.polymer.2014. 12.044 100. Zaikin AE, Zharinova EA, Bikmullin RS (2007) Specifics of localization of carbon black at the interface between polymeric phases. Polym Sci Ser A 49:328–336. https://doi.org/10. 1134/S0965545X07030145 101. Göldel A, Marmur A, Kasaliwal GR et al (2011) Shape-dependent localization of carbon nanotubes and carbon black in an immiscible polymer blend during melt mixing. Macromolecules 44:6094–6102. https://doi.org/10.1021/ma200793a

Part IV

Applications of PTT

Chapter 11

Industrial Applications of PTT-Based Polymer Blends, Composites, and Nanocomposites S. Hema, Sreedha Sambhudevan, C. Sreelekshmi, Malavika Sajith, and K. Rashid Sulthan

1 Introduction Engineering plastics are widely used in the automotive industry. Use of these polymers and composites helps in decreased weight, increased conveniences, and safety precautions that are usually deployed for the engineering resins to maximize technical production. The origin of most of the plastic technology is non-renewable petroleumbased substrates [1]. The use of these plastics helps in improving the fuel economy, recyclability, and renewability of plastic parts. Chemical substrates derived from renewable resources are now equivalent to petroleum-based analogs. One of the examples is poly (trimethylene terephthalate) (PTT). PTT is a bio-based thermoplastic industrial polymer that is marketed by DuPont [2]. Green technology has aided PTT’s marketing and development efforts substantially. An industrially innovative polymer engineering platform has been created in DuPont’s China research and development center to service the regional China market with PTT manufacturing and development assistance. They also looked at the latest industrial applications for PTT and moderations, including the expanded applications into the field of engineering polymers (EP), developing flame retardancy property and regulating the melt viscosity for PTT fiber spinning, and hence finding the applicability in PTT nanocomposites. PTT is an aromatic polyester that shows the mechanical features of both polyethylene terephthalate (PET) and excellent processing characteristics of polybutylene terephthalate (PBT). But it is regarded as a brittle polymer due to the presence of sharp notches and curvature of the material. The incorporation of elastomeric materials or inorganic polytrimethylene terephthalate fillers in the PTT matrix can

S. Hema · S. Sambhudevan (B) · C. Sreelekshmi · M. Sajith · K. Rashid Sulthan Department of Chemistry, Amrita Vishwa Vidyapeetham, Amritapuri, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. R. Ajitha and S. Thomas (eds.), Poly Trimethylene Terephthalate, Materials Horizons: From Nature to Nanomaterials, https://doi.org/10.1007/978-981-19-7303-1_11

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improve resilience [3]. The condensation reaction of 1,3-propanediol (a fermentation product) and petroleum-derived terephthalic acid (TPA) or dimethyl terephthalate (DMT) results in an eco-efficient performance fiber called Sorona. The Sorona fiber, which is made from renewable resources, is the first industrial illustration of DuPont’s contribution to developing an innovative solution to reduce the world’s reliance on fossil fuels and greenhouse gas emissions. Some recent research describes methods for improving the toughness of this PTT by combining a polymer with a suitable chemical functionality during processing. This functionality is characterized by the interactivity between molecular fragments, and it gives good dispersion and better interfacial adhesion, resulting in mechanical enhancement [4]. The properties of PTT blends are affected by the various components’ composition and their supermolecular structure. The phase structure of various fibers depends on their rheological properties and the interphase bond between the components. Blends of PP/PTT would have unique processing properties. These properties would enable various industrial applications. Melt spinning was used by Opperman et al. to create PET/PTT–blend fibers. At a concentration of 10%, PTT considerably improves recovery during cyclic deformation of PET fibers. PET fibers with a 30% PTT content show full recovery properties. Various researchers have revealed that the catalyst choice has a significant impact on the reaction rate and PTT characteristics. Titanium, tin, and antimony compounds, which are often used catalysts, each have their own set of constraints [5]. To improve toughness without losing overall performance, poly (trimethylene terephthalate) was melt-blended with maleinized acrylonitrile–butadiene–styrene. ABS-g-MAH has the benefit of high toughness, superior processing qualities, and increased molecular polarity [6]. Bio-based 1,3-propanediol (PDO), a renewably sourced building block, is developed successfully by DuPont by using glucose as the raw material through industrial biotechnology. The use of this green technology has significantly increased the commercialization of PTT and also their development activities [7]. DuPont’s industrial polymer technology platform in China serves PTT manufacturing in local China markets. Due to the low melt viscosity, poor temperature impact strength, and low heat distortion temperature, it has fewer potential applications [8]. PTT has remained unclear since its one of the monomers, namely 1,3- propanediol (PDO), was not easily available. On the introduction of this monomer commercially in 1998, the interest in PTT for fiber, film, and engineering has also increased [9]. After long years, the fiber industries are aware of the fiber application of PTT, and they understood that PTT is very suitable for making the Fiberfil and carpets because of its low modulus, better bending, and work recoveries than PET. On comparing the elastic recovery and lower modulus of other polyesters, it was found that PTT has these properties better than both PET and PBT. These properties make them use it for the manufacturing of carpets, etc., and hence, it becomes a challenge to chemical and fiber companies to develop technologies to develop PDO at lower cost and to commercialize PPT [10–12].

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2 PTT-Based Polymer Blends Blending has received a lot of interest as a simple and cost-effective way to produce polymeric materials with a wide range of commercial uses. PTT-based polymer blend is made up of PTT and other polymers that have been mixed to develop a new material with a variety of physical properties. Generally, the blends of PTT include PTT-thermoplastic blends, PTT-rubber blends, PTT-thermosetting blends, and PTT-filler blends and are extensively studied. By choosing the right component polymers, the characteristics of the PTT blends may be tailored to their intended purpose [13]. Today’s market pressure is so intense that industrial manufacturers must develop better and more cost-effective materials with superior combinations of characteristics to replace conventional metals and polymers. Blending can be utilized to create materials with superior characteristics than the basic polymers. Because of their commercial relevance, PET and PTT blends have been extensively investigated. PET crystallizes slowly, while PTT crystallizes quickly and readily without the use of a nucleating agent. As a result, combining PET and PTT will provide an intriguing approach to combine the polymers’ complimentary characteristics [14]. In the amorphous form, PET/PTT blends are completely miscible according to microscope morphology and thermal transition criteria. To produce filaments, polyester (PET) and poly (trimethylene terephthalate) (PTT) chips were melted mixed together and spun. Not only did the Tg of the mix fibers drop, but so did the melting point and crystallization temperature. The Tg of a fiber structure decreases as the length of the aliphatic chain increases. Because of the suppression in the glass transition temperature (Tg) of the PET due to the presence of PTT in the blend, which has a lower Tg, the optimum dyeing depth for the blended fibers was obtained at 1100C instead of 1300C required for normal PET fibers when dyed with high energy disperse dyes. In addition, the dyeing depth of melt mix fiber was much greater than that of virgin PET. The colored samples’ fastness was also found to be comparable to that of dyed virgin PET fiber, with a little drop in tensile strength of the fibers [15] (Table 1). During the process of blending, factors like phase structure of immiscible components, their characteristics, and the supermolecular structure of the different ingredients all influence the properties of the PTT. The rheological characteristics of the components, as well as adhesive interactions in the interphase, have a major impact Table 1 The tensile strength, Elongation at break and % of crystallinity for PET and its blend fibers [13] Nature of sample

Tensile strength (MPa × 10–2 )

% Decrease in tensile strength

Elongation at break (%)

% Crystallinity from XRD

PET 100%

5.29

–

82.60

22.12

PET/PTT (90/10)

5.19

1.89

79.40

23.42

PET/PTT (80/20)

5.13

3.02

78.00

23.57

PET/PTT (70/30)

5.00

5.48

74.00

23.63

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on the phase structure of the fibers, which is based on a heterogeneous polymer mix. The Taylor–Cox relationship on viscosity ratio K (K 14 hdhm), where hd is the viscosity of the dispersion phase and hm is the viscosity of the matrix, governs the size and shape of deformed particles in the dispersed phase of blends [16]. PTT produces a miscible mix of PET, PBT, and other polyesters with a single Tg for each blend composition. The Gordon–Taylor equation accurately predicts the Tg’s dependency on blend composition. The thermal characteristics of PTT blends with PET, PBT, and polyethylene naphthalate (PEN) have revealed mutual miscibility above the melting point as well as in the amorphous phase below the melting point, according to research. Polyester blend components crystallize and create their own crystalline variations below the melting point. With increasing concentrations of the minor polyester component, total crystallinity of the pure component diminishes [17]. Melt spinning was used by Opperman et al. to create PET/PTT–blend fibers. At a concentration of 10% wt%, PTT greatly enhances recovery during cyclic deformation of PET fibers. PET fibers with 30 wt% PTT have full recovery properties. Furthermore, PET/PTT–blend fiber color more quickly than PET or PTT fibers alone. The temperature ranges from 100 to 1108 degrees Celsius for PET, 908 degrees Celsius for PTT, and 80 to 858 degrees Celsius for mix fibers containing 10–30% PTT. In a mix with PET, polybutylene terephthalate (PBT) is less effective than PTT [5]. Dyeable PP/PET–mix fibers are created by blending PET with PP before spinning and employing dispersion dyes at low PET concentration (8–10 wt%) in PP. In addition, as compared to PP fibers, the elastic characteristics of mix fibers were enhanced. The greater melting point of PET in comparison with PP and the high processing temperature are disadvantages of PP/PET mixing (about 2808C). Blends of PP/PTT and PP/(PTT/PET) are predicted to provide unique processing features and qualities of blend fibers based on these intriguing thermal and physical–mechanical properties of PTT and its blends with another PES [18]. Twin-screw extruders were used to make PA6/PTT blends after combining poly (trimethylene terephthalate) (PTT) with polyamide 6. (PA6). Water immersion experiments were used in conjunction with SEM and DSC to evaluate the water absorptivity of the PA6/PTT blends. The results demonstrate that as the PTT concentration increases, the quantity of absorbed water in the blends decreases, indicating that the PTT phase may effectively prevent the PA6 phase from absorbing water. Mechanical tests further demonstrate that after absorbing water under the same circumstances, PA6/PTT mixes have clearly superior mechanical characteristics than pure PA6. After absorbing water, the tensile and bending yield strength of PA6/PTT are increased by 20.89 and 71.73%, respectively, when compared to pure PA6 [19]. A broad range of morphological features may be observed when both components of a binary blend crystallize at the same time. A liquid–liquid (L-L) demixing procedure can occasionally impact the morphologies of crystalline polymer blends in addition to crystallization. Crystallization may occur simultaneously with L-L phase separation when the mix has a phase diagram. The two competing processes may produce distinct morphological patterns that neither process could achieve on its own. The blend of poly (ethylene terephthalate) (PET) and poly (trimethylene

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terephthalate) (PTT) displayed a distinctive morphology generated by combined crystallization and L-L demixing, according to recent research by L. K. Hee et al. [20]. Using a twin-screw Brabender, the thermal behavior, morphology, and esterinterchange reaction of poly (trimethylene terephthalate) (PTT)/Poly (ethylene terephthalate) (PET) melt blends were studied across the whole composition range (xPTT/(1-x) PET). The ester-interchange reaction in the PTT/PET mix was discovered to be the cause of melt blends. Transesterification between PTT and PET rises with increasing blending time, increasing the unpredictability of the copolymer. This reaction makes the blends more homogeneous and reduces the degree of crystallinity in the melt blends. When compared to pure PTT, mechanical characteristics of PTT-rich blends decline as PET concentration increases. Tensile modulus falls with increasing PTT concentration in PET-rich blends, while tensile strength and elongation are comparable to pure PET [21].

2.1 Different Types of PTT Blends Extruder melt spinning was used to make polypropylene (PP)/polyester (PES)–blend fibers. Marcincin et al. fabricated a polymer blend consisting of PP and a “master batch” (MB) based on polytrimethylene terephthalate (PTT) or polyethylene terephthalate (PET), binary PTT/PET or PP/PTT blends, as well as a ternary PP/(PTT/PET). The phase structure of PP/PES–mix fibers was investigated, and it was discovered that PES microfibers in blend fibers are separated from the PP matrix. The effect of MB composition and rheological properties on phase structure parameters suggests that the PTT in the binary MB has a substantial impact on the length of distributed PES microfibers in the PP matrix. The diameter and length of the PES microfibers are lower in PP and ternary MB (PP/PTT/PET) blends. The addition of PTT/PET (PES) in the blend PP/PES fibers improves the structural and mechanical characteristics. Furthermore, when a binary MB is employed, PTT enhances the tensile strength of the PP/PES–blend fibers, but when a ternary MB is utilized, fiber nonuniformity is decreased [18]. Two immiscible polymeric blend systems of poly (trimethylene terephthalate) (PTT)/polyamide-12 (PA12) and PTT/polyethylene (PE) with different levels of molecular interactions were investigated as model systems to describe the rheological behavior of polymer blends using emulsion-based (Palierne theory) as well as micromechanical models (Coran approach). For both systems, there was no meaningful agreement between experimental data and Palierne model predictions, which was associated with a high viscosity ratio and dispersed phase content. Nonetheless, as compared to the PTT/PA12 system, the PTT/PE blend, which has practically little interfacial thickness due to the lack of intermolecular contact, appeared to have a superior correlation with experimental results. Furthermore, in the mix where the viscosity of the dispersed phase was higher than that of the matrix, there was a better agreement between actual and theoretical data. Palierne’s projected values were also

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closer to actual data at higher frequencies in both model systems, most likely owing to a breakdown in physical network structure. Because of its micromechanical origins, Coran analysis may produce outputs that are in good agreement with experimental data in both model systems [22]. Other polyesters, polyamides, thermoplastic elastomers, epoxy resins, and polyolefins (linear low-density polyethylene, LLDPE, and polypropylene) have been blended with PTT. Xue et al. in 2007 found an increase in the crystallization rate for an immiscible combination of PTT and polypropylene. PP-grafted-maleic anhydride (PP-g-MA) was added to the system as a compatibilizer. After combining PTT and PP, the researchers discovered that mechanical characteristics were balanced. The impact characteristics of the notched Izod polymer, on the other hand, were lower than those of both plain polymers [23]. Drown et al. in 2007 integrated several organoclays into a PTT matrix, observing a rise in heat deflection temperature and tensile properties, as well as a peak in tensile modulus, at a loading of 3 wt percentage organoclay [24]. PTT and BioPE polymer blends have been successfully produced and characterized. In terms of mechanical characteristics, phase morphology was critical for the polymer blends. When the PE concentration was high, the BioPE phase altered the tensile characteristics. Because morphology had no effect on flexural characteristics, a balance of properties was observed between the clean polymer values. The impact strength grew to values larger than the plain polymers once the mix transitioned from co-continuous to PTT as the predominant phase. The impact strength of the blend system was reduced below the characteristics of each individual polymer due to the heterogeneity in the system [25].

2.2 Important Applications of PTT Blends Because of its outstanding performance, the PTT (polytrimethylene terephthalate) fiber has been widely utilized in the apparel industry; however, the use of its short fibers blended fabric requires more study. Fabrics such as cotton and modal are being used to manufacture lightweight underwear. The air permeability, moisture permeability, heat resistance, and wicking of PTT/Viloft/Spandex, JC/PTT/ Spandex, Modal/PTT/Spandex, FI-R/PTT/ Spandex, and Linen/PTT/C/ Spandex mixed knitted fabrics of the same count were tested and assessed. The gray pertinence technique was used to conduct a complete evaluation of fabric heat-moisture comfort performance, with the conclusion that the Linen/PTT/C/ Spandex-blended fabric has the best heatmoisture comfort performance. It provides some theoretical backing for the use of knitted textiles manufactured from PTT-mixed materials in the underwear industry [26]. The production of super-toughened PTT blends with high impact strength is both scientifically important and commercially lucrative. This is due to the fact that high toughness allows materials to be used in a far wider range of applications. To create a super-toughened material with enhanced stiffness, a flowable and partly crosslinked elastomer mix based on ethylene acrylate copolymers was added to PTT

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resin. The zinc ion in the elastomer catalyzed the interaction between the epoxy and end groups of PTT resin, promoting interfacial compatibility between the PTT matrix and the crosslinked elastomer phase. The EMMA-GMA/EMAA-Zn elastomer with rich epoxy groups was found to be an effective impact modifier in PTT resin [27]. The conducting polymer blend nanocomposites have high dielectric loss and high conductivity and have attracted great interest in the scientific field mainly in EMI shielding and also an EMI shielding material since it can reduce the force of unwanted electromagnetic radiations coming from the electronic devices [28, 29]. The shielding of electronic devices helps the protection of surroundings and parent devices from the adverse effect on electromagnetic radiation. Ajitha et al. investigated the effects of the addition of MWCNTs on the electrical and EMI shielding performance of PTT/PP (polypropylene) immiscible blends. With the inclusion of MWCNTs, the dielectric and EMI shielding performance increased, and this improvement in electrical characteristics is attributed to the creation of a continuous conducting network of MWCNTs. It can enhance the passage of free electrons through networks, resulting in the formation of continuous conducting channels. As a result, this composite material may certainly be recommended for efficient EMI shielding, particularly in mobile phones with a minimum thickness of 2 mm and high SE values [30].

Fig. 1 Applications of PTT blends

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3 Poly (Trimethylene Terephthalate) (PTT) Composites Polymer composites, the most unique application of polymers, are multiphase solid materials. Polymer composites consist of 2 main phases-matrix, a continuous phase, and reinforcement, a discontinuous phase. Matrix helps in reinforcement’s bonding, and reinforcements give strength to composites. Poly (trimethylene terephthalate) (PTT) composites are those in which PTT is regarded as a matrix; they have very good mechanical strength, stiffness, excellent fatigue, and fracture resistance and are corrosion resistant, which is hardly possible with individual components [31]. Scientists have developed a number of techniques to enhance the interfacial adhesion between natural fiber and PTT matrix. There are well-established methods for treating natural fibers with alkali, silane, etc. To improve fiber-PTT interaction and increase their potential as reinforcing agents, natural fibers are chemically treated. However, utilizing functionalized polymers as a compatibilizer for thermoplastic/natural fiber composites, as well as treating the natural fibers, has shown to be beneficial [32]. Compatibilizers with functional groups such as anhydrides, isocyanates, and epoxies, among others, can help improve the interfacial adhesion between the fiber and the matrix. By reacting with hydroxyl groups, the compatibilizer can lower the natural fiber’s hydrophilic character and increase compatibility with the hydrophobic polymer matrix [33]. J. P. Reddy and colleagues investigated the use of PMDI as a compatibilizer in natural fiber-reinforced polymer composite materials, and researchers discovered that the isocyanate moieties of PMDI interact with the hydroxyl groups of the polymer and natural fiber. Natural fiber-reinforced thermoplastic composites, on the other hand, have a significant disadvantage in terms of impact strength. In addition, PMDI can increase the tensile and flexural characteristics of SG fiber-reinforced composites without compromising the impact strength [34]. The TEM picture (Fig. 2a) depicts a PTT/ZnO composite arising from a low concentration of Zn(acac)2 (2 wt.%), in which nanoscale ZnO particles are seen without aggregation. When the Zn(acac)2 loading is raised to 10%, a cluster of ZnO particles appears (Fig. 2b), and the electron beam diffraction pattern shows that the ZnO clusters are crystalline (Fig. 2c). PTT/CuO composites, PTT/MgO composites, PTT/Al2 O3 composites, and PTT/Fe3 O4 composites were fabricated using the same technique. The PTT/ZnO composites were characterized using XRD. Figure 2c shows the XRD result for pure PTT polymer, whereas Fig. 1d shows two distinct peaks for the low-loading ZnO PTT composite, which are marked by a circle in the picture and correspond to the (100) and (002) facets of ZnO crystals [4, 35]. In addition to application development research, PTT nanocomposite is an example of basic research in the scientific world.

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Fig. 2 TEM images for: a PTT/ZnO composite with low procurer loading (2.0%); b PTT/ZnO composite with high Zn(acac)2 loading and the XRD results for: c pure PTT polymer; d PTT/ZnO composites (low loading) [4]

3.1 Classification and Fabrication methods of PTT composites PTT/Short Glass Fiber Composites were synthesized by M. Run et al. in 2010. They studied the structural and physical properties of composites and found that there is a strong attraction between PTT matrix and SGF, and as a result, the tensile strength, Young’s modulus, and thermal stability increased compared to individual components. The composite with SGF content 10–20 wt% shows improved properties. For the fabrication, they used raw materials such as PTT homopolymer, silane coupling agent (c-aminopropyl methyl di-methoxy silane), and glass fiber which has to undergo glass fiber treatment. The composites were prepared in the ZSK25WLE WP-type self-wiping, co-rotating twin-screw extruder. It is operating under a screw speed of 120 rpm and 2608C die temperature. The composite ribbons obtained are cooled in cold water, cut, and re-dried [36]. The addition of chopped glass fiber to the PTT matrix improved the tensile strength, impact strength, and flexural strength. The thermo-mechanical properties of these show that it is a trustworthy material for automobiles and building products [37]. J. P. Reddy et al. studied the properties of PTT/CGF composites and found that PP-gMA (Polypropylene-graft-maleic anhydride) acts as a coupling agent improving the

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adhesion between CGF and PTT matrix. Raw materials like PTT and glass fiber modified with PP-g-MA were used and prepared using a twin-screw extruder at temperature of 230–245 °C and speed of 100 rpm. The composite pellets then undergo injection molding at Barrel temperature 235 °C and mold temperature 35 °C. To improve the impact strength of the bio-composites, a prepolymer called methylenediphenyl-diisocyanate-polybutadiene (MDIPB) was employed. The polymeric ethylene diphenyl-diisocyanate (PMDI) compatibilizer was also employed to improve the composites’ mechanical characteristics. PTT, SG fibers, MDIPB prepolymer, PMDI compatibilizer, RUBINATE PTT, and SG were dried for 4 h in an 80 °C hot air oven. A micro-extruder was used to make the composites. The screw rotation speed was 100 rpm, and the L/D (length to diameter) ratio was 18. The processing temperature was 235 °C, and the L/D (length to diameter) ratio was 18. The molten mix was transferred to a preheated micro-injection molding machine after a predetermined processing period (2 min to avoid further thermal deterioration of SG fiber) in the micro-extruder. The injection molding pressure was optimized (beginning stroke 5, and final stroke 6 bar for clean PTT), and the mold temperature was kept constant [38].

3.2 Applications of PTT Composites PTT is particularly appropriate for engineering applications because it combines the physical qualities of PET with the processing characteristics of PBT [4]. The objective of this study was to see if composites might be used as an effective low-weight electromagnetic interference (EMI) shielding material in the frequency range of 12.4–18 GHz, poly (trimethylene terephthalate) [PTT]/multi-walled carbon nanotube [MWCNT] composites with varying amounts of MWCNTs were fabricated. CNTs can improve the mechanical, thermal, and electrical characteristics of PTT, according to recent research. The addition of PTT to the family of EMI shielding materials by fabricating MWCNT-reinforced PTT composites demonstrated that composites containing 5–10% (w/w) MWCNT can be used as an effective, lightweight EMI shielding material because the electrical conductivity, permittivity, and EMI SE of composites were found to be dependent on MWCNT concentration and increased with increasing MWCNT load [39]. In agronomy, biocarbon has been utilized as a soil amendment agent to improve the retention or absorption of certain chemicals, and biocarbon derived from Peanut hulls pyrolyzed at temperatures between 500 and 1000 °C has also been used to generate anodes for lithium batteries. M. Picard et al. have focused on the valorizations of peanut hulls through the creation of green composites. The peanut hull biocarbon was mixed with 80 wt.% poly (trimethylene terephthalate) at a ratio of 20 wt.% peanut hull biocarbon to 80 wt.% poly (trimethylene terephthalate) (PTT). The flexural and tensile moduli of the resultant composites increased by at least 130%, while the renewability content increased by 48%. One of the many possible, sustainable, and

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value-added applications for peanut hulls is the production of peanut hull biocarbon composites [40].

4 PTT-Based Nanocomposites PTT is an aromatic polyester with methylene substituents and is derived mostly from petroleum products. PTT-based nanomaterials are of greater importance for the past decades, and they have been most studied. The nanocomposites based on PTT bear excellent resistance toward cracks and breaks, good elasticity, and dyeability as it displays composition and structural change over a nanometer length scale [30]. Hybrid PTT-inorganic nanosystems bear excellent thermal and mechanical features and the improved physiochemical properties attributed to the uniform dispersion of particles as a reinforcing phase over the engineering matrix. The successful dispersion of nanofillers can ensure PTT is used as a low-cost solution for many potentially useful materials [41].

4.1 Fillers used in PTT matrix Nanoscaled fillers are materials used in polymers to enhance the properties relative to conventionally scaled ones, because of the small interfacial area, macroand micro-sized fillers have little interaction with the PTT matrix. The use of nanofillers on PTT will upgrade different barrier properties due to the huge aspect ratios. Nanofillers can be one-dimensional CNTs, two-dimensional nanoclay particles, three-dimensional nanogranules, nanocrystals, and nanospherical particles in shape. Clays are frequently incompatible and difficult to distribute in a PTT matrix. As a result, the organic alteration of the clay’s surface by a specific organic surfactant has been employed to help in its dispersion. Organophilic affinities of fillers toward the PTT matrix can be achieved through chemical functionalization. Better dispersion, good interfacial adhesion, and non-toxic method of preparation enable nanofillers to be unique and eco-friendly [42]. Interchange/exchange reactions have a significant impact on the characteristics of reactive polymer mixtures. The impact of nanofillers on these reactions, especially trans-reactions, is still unknown. J. Seyfi et al. examined the effects of nanoclay loading on trans-reactions and their impact on the thermal degradation behavior of phenoxy/PTT blends. The results revealed that the amount of trans-reactions reaches its maximum with only 1 wt.% nanoclay added. This encouragement of trans-reactions was a foreshadowing of the emergence of locally restricted habitats. This so-called nanoconfinement of polymer chains surrounding silicate layers, according to the hypothesized mechanism, might be responsible for an increase in

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the amount of trans-reactions between the blend components. The degree of transreactions was also seen to decrease as the quantity of nanoclay content increased, which was attributed to the intercalated structure of nanocomposites [43].

4.1.1

Organic Filler-Based PTT Nanocomposites

Potential organic particulates in nanoscale at different loading levels are evaluated as a means to enhance the performance of PTT-based nanocomposites. This category of organic fillers is known to be good for less hazards to human health and the environment as most of them are eco-friendly and degradable. Reduced specific weight compared with other mineral fillers makes them a better candidate for lowcost PTT nanocomposites [44]. The role of organic fillers as incorporated into the PTT matrix is to form complex interphase, thereby modifying the configuration and interaction of the filler-PTT matrix. Among different organic fillers, cellulosic fillers like MCC and NCC are interesting as they are capable of improving mechanical and water barrier properties [45]. Among different bio-based fillers, nanocellulose fibers attracted researchers as they possess unique features than inorganic fillers. The main advantages of cellulose include its renewable nature, high specific strength and modulus, low density, low thermal conductivity, and the ability to recycle [46].

4.1.2

Inorganic Filler-Based PTT Nanocomposites

Nano-inorganic fillers belong to particulate fillers with excellent size-dependent physical properties. In nano regime, they dramatically modify macroscopic physical and mechanical properties of PTT-based composites even at lower concentrations of filler content. Usually, filler’s surface might be modified to improve adherence to the PTT matrix [47]. Because of their nanoscale size and intercalation/exfoliation characteristics, inorganic clays like montmorillonite and hectorite have been utilized as reinforcing components in different polymers. Clays are frequently incompatible and difficult to distribute in a polymer matrix. As a result, the organic alteration of the clay’s surface by a specific organic surfactant has been employed to help in its dispersion. Clay platelets in exfoliated nanocomposites have also been demonstrated to function as an efficient nucleating agent, increasing crystallinity and crystallization rate. According to the findings of L. Smith et al., clay affects the crystallization behavior of PTT, causing the rate of crystallization to be increased [48]. The chemical and mechanical characteristics of PTT-based nanocomposite materials were studied in the presence of functionalized inorganic filler by Chin-San Wu et al.; due to the formation of ester linkages from the condensation of the carboxylic acid groups of PTT-g-AA with the hydroxyl groups of MWNT–OH, the functionalized PTT-g-AA/MWNT–OH mix had significantly improved thermal and mechanical characteristics [49].

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Carbonaceous nanofillers like graphene and carbon nanotubes (CNTs) have a bright future because of their superior structural and functional characteristics and a wide variety of uses [50]. It is difficult to achieve a uniform dispersion of CNTs in the PTT matrix due to their insolubility and the fundamentally poor compatibility of the two phases. Several techniques for improving phase compatibility between CNTs and PTT have been proposed, including functionalization of the nanotubes themselves, such as anchoring to the matrix polymer. Silica obtained from silicon precursors is known to have enhanced physical as well as mechanical features of PTT nanocomposites [51]. Such a system prepared via the sol–gel technique allows the grafting of PTT chains on the surface of silica. Melt compounding and compression molding were used to make polymer composite materials using poly (ethylene terephthalate)–poly (trimethylene terephthalate) blends as the matrix and various microcrystalline cellulose (MCC) filler levels (0–40 wt%). According to the DSC data, the MCC addition has no consistent or significant effect on the glass transition (T g), melting (T m), or crystallization temperature of the composites. Because of the MCC’s reinforcing action, dynamic mechanical characteristics improved as MCC content increased. The DMTA tan peak values did not alter much when the MCC concentration rose. With increasing MCC concentration, the start temperature of fast thermal degradation is reduced, according to TG. The thermal stability of the composites was also observed to be somewhat reduced as the MCC concentration increased [52]. A novel class of nanocomposites comprising poly (trimethylene terephthalate; PTT) and single-walled carbon nanotubes (SWCNTs) was created using a simple method, and it was discovered to be a high-performance engineering material with a high modulus [53].

4.2 Synthesis of PTT Nanocomposites Various intercalation techniques, including solution, melt, and in situ polymerization, were used to create different nanocomposites. Thermal assistance pyrolysis of metal acetylacetonate was utilized to manufacture nanoparticles of PTT-metal oxides using precursors comprising single nanoparticles. Instead of the usual high vacuum twostep polycondensation reaction, PTT-metal oxide nanocomposites were prepared using a one-pot strategy, as illustrated in Scheme 1. The manufacture of PTT-metal oxide nanocomposites in a single pot varies from the traditional two-step high vacuum condensation polymerization technique in a few ways. At room temperature, metal acetylacetonate was combined with dimethyl terephthalate (DMT), 1,3-propanediol (PDO), and the catalyst. To remove the methanol and generate PTT polymers, the temperature of the mixture is raised to 200–218 °C. Under a high vacuum, the reaction temperature is increased to 250–260 8C in the second stage to eliminate PDO and produce high molecular weight PTT [4].

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Scheme 1 In situ decomposition of metal acetylacetonates during high-temperature polycondensation to form nanocomposites [4]

In situ polymerization technique was used by Szymczyk et al. for the synthesis of nanocomposites based on COOH-functionalized multi-walled carbon nanotubes on PTT matrix. It was difficult to control the uniform dispersion of CNT over the PTT due to the intermolecular force of attraction between the nanotubes and the long bundles of CNT restricting the exfoliation. Initially, CNT was mechanically and sonically dispersed to N-Methyl-2-Pyrrolidone, ensuring homogeneous dispersion of MWCNT over the PTT matrix. Functionalization of carboxylic acid here affects the synthesis of PTT nanocomposites, and it possesses a higher degree of crystallinity than that of pure PTT [54] (Scheme 2). L. Smith et al. reported that while synthesizing PTT nanocomposite it was challenging to completely exfoliate the clay particles; however, they used a novel two-step technique of solution blending followed by a melt processing of converting liquid

Scheme 2 Preparation method of nanocomposites [48]

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melt into a solid article of defined shape and structure. The suspension of Cloisite 15A, PTT, and trifluoracetic acid was sonicated, and later, the vigorous string ensures homogenous dispersion. These nanocomposite films were then sandwiched between Teflon sheets and melt-pressed at 260 °C in a Carver press between two preheated platens, then quenched in an ice-cold water bath to stop further crystallization [48]. The sol–gel technique is a quick and easy way to make inorganic structures. It has a number of benefits, including the ability to regulate size distribution by adjusting pH, concentration, and temperature. In 2018, Anil Kumar et al. synthesized nanocomposite films of PTT-Silica with varying amounts of tetraethoxysilane (TEOS). During the hydrolysis and condensation reactions, silica particle was added directly to PTT trifluoracetic acid mixture. In the PTT matrix, the size of the nanofillers was discovered to be around 80,100 nm. Homogeneous dispersion of nanoparticles is found up to 5 wt% of silica, while non-uniform dispersion is visible for those with more than 5% TEOS content, according to SEM data. In comparison with plain PTT, the crystallinity of PTT nanocomposites improved as the TEOS concentration increased. The size of the spherulites was discovered to be dependent on both the crystallization temperature and the silica concentration. The size of the spherulite grew as the crystallization temperature climbed from 120 to 180 °C, but the size of the spherulite reduced as the TEOS concentration increased at a given crystallization temperature, showing that adding silica to PTT changes its crystallization behavior [55]. About 2–5 wt% organoclay containing PBT/PTT blends was fabricated using a co-rotating twin-screw extruder. Here, nanosized organoclay (Cloisite 30B) takes the role of a substance that increases the durability of extruded blends and hence acts as an impact modifier. To toughen the polymeric matrices, an impact modification called ultra-low-density polyethylene-grafted glycidyl methacrylate (ULDPE-gGMA) was employed. The quantity of impact modifier (ULDPE-g-GMA) in all of the prepared nanocomposites is the same, i.e., 2% by weight. In Izod impact testing, a 2percentage impact modifier (ULDPE-g-GMA) was shown to be adequate to improve the notched Izod impact strength of the neat PBT and neat PTT by 85.6 and 98.6%, respectively. With ULDPE-g-GMA rubber, it displays outstanding toughening of PBT and PTT. It was also discovered that adding just 3 wt% organoclay to PBT/PTT blends increased tensile strength and tensile modulus considerably. The nanocomposite with 3 wt% organoclay in PBT/PTT/2 (wt%) ULDPE-g-GMA showed no phase separation in FEG-SEM studies. It was discovered that 3 wt% organoclay was uniformly distributed in nanocomposites based on impact-modified PBT/PTT blends [56].

4.3 Applications of PTT Nanocomposites PTT is a semi-crystalline polymer that combines the benefits of polyesters and polyamides, having a primary use in the textile sector. PTT is a promising candidate for being combined with a variety of nanoparticles to increase its usefulness [57]. After incorporating several types of nanoparticles into engineering polymers,

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Fig. 3 Applications of PTT nanocomposites

significant increases in final characteristics have been found. Nanofibrillar composites of PTT are known to have more and more applications in recent years as they possess bright applications in different fields. The shape and size of the dispersed phase here strongly influence the final properties of composites. The majority of PTT nanocomposite application development has so far been concentrated on textile and carpet fibers since this polyester has a unique mix of characteristics that make it ideal for these applications [58]. PTT nanocomposite in fibers, injection moldings, and film manufacturing has excellent tensile properties, elastic recovery, and dyeability. Furthermore, [59] nanofibers of PTT are known to be popular for its excellent tensile strength, nylon-like softness, and chemical inertness. PTT fibers with enhanced resistance to stain make them a wise candidate to be used as carpets and textile fiber applications, and the nanocomposites can be utilized as an engineering thermoplastic (Fig. 3).

5 Conclusion One of the most significant commercial polyesters is polytrimethylene terephthalate (poly-1,3-propylene terephthalate, or PTT). Tensile and flexural strength, dimensional stability, flow, and surface finish are all advantages of PTT-based blends and composites. It has the same chemical resistance as PBT-based systems. It is also a suitable choice for a variety of industrial applications, including automotive components, smartphone housings, and a variety of other industrial and retail goods, textiles, and thanks to its good dimensional stability and finishing capabilities. However, it is utilized on a considerably lesser scale than PET and PBT. The rate of increased

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industrialization of PTT is influenced by two key factors: extremely effective polymer synthesis and processing technologies and the price of PDO. However, PTT fibers provide an entirely new way to develop consumer textiles, with improved processing and application properties. Finally, the cost of PTT will determine how quickly it replaces other fibers. PTT’s genuine earnings are disguised in enormous amounts.

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55. Bodempudi AK, Vasanthan N (2018) Crystallization studies of poly(trimethylene terephthalate)/silica nanocomposites prepared by sol-gel technique. ACS Omega 3(12):17797–17804. https://doi.org/10.1021/acsomega.8b02816 56. Nayak SK, Mohanty S (2010) Poly (trimethylene) terephthalate/m-LLDPE blend nanocomposites: evaluation of mechanical, thermal and morphological behavior. Mater Sci Eng A 527(3):574–583. https://doi.org/10.1016/j.msea.2009.08.026 57. Chuah HH (n.d.) Synthesis, properties and applications of poly(trimethylene terephthalate). Wiley Ser Polym Sci 361–397. https://doi.org/10.1002/0470090685.ch11 58. Li MF, Xiao R, Sun G (2011) Morphology development and size control of poly(trimethylene terephthalate) nanofibers prepared from poly(trimethylene terephthalate)/cellulose acetate butyrate in situ fibrillar composites. J Mater Sci 46(13):4524–4531. https://doi.org/10.1007/ s10853-011-5346-6 59. Huang C-L, Wang Y-J, Fan Y-C, Hung C-L, Liu Y-C (2016) The effect of geometric factor of carbon nanofillers on the electrical conductivity and electromagnetic interference shielding properties of poly(trimethylene terephthalate) composites: a comparative study. J Mater Sci 52(5):2560–2580. https://doi.org/10.1007/s10853-016-0549-5

Chapter 12

Textile Applications of PTT-Based Polymer Blends, Composites, and Nanocomposites Abjesh Prasad Rath and M. K. Kanny

Abbreviations PTT PET PBT PES BCF POY SDY EPDM PC PEI PP PLA PS PMC HDT GNS CNT

Polytrimethylene terephthalate Polyethylene terephthalate Polybutylene terephthalate Polyethersulfone Bulk continuous filaments Partially oriented yarn Spin-draw yarn Ethylene propylene diene monomer Polycarbonate Polyetherimide Polypropylene Polylactic acid Polystyrene Polymer matrix composites Heat distortion temperature Graphene nanosheets Carbon nanotube

A. P. Rath (B) Laboratory for Advanced Research in Polymeric Materials (LARPM), School for Advanced Research in Petrochemicals (SARP), Central Institute of Petrochemicals Engineering and Technology (CIPET), Patia Bhubaneswar 751024, India e-mail: [email protected] A. P. Rath · M. K. Kanny Composites Research Group, Department of Mechanical Engineering, Durban University of Technology, Durban 4000, South Africa e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. R. Ajitha and S. Thomas (eds.), Poly Trimethylene Terephthalate, Materials Horizons: From Nature to Nanomaterials, https://doi.org/10.1007/978-981-19-7303-1_12

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1 Introduction to PTT-Based Polymer Blends, Composites, and Nanocomposites: Processing and Characterization PTT is a thermoplastic material and newly commercialized polymer with qualities similar to PET, the most widely used polyester in fabrics, carpeting, and garments. PTT is also utilized in the textile industry, but it has better elastic recovery than PET, which makes it a better choice for fabrics. It is a thermoplastic that can be spun into fibers and yarns, and it is used in carpeting, textiles, and garments, as well as engineering thermoplastics, nonwoven fabrics, films, and monofilaments. Whether utilized in carpet, clothes, home furnishings, or automotive materials, polymer combines the greatest qualities of nylon and polyester. Its fiber appears to be younger. PTT fibers feel softer, dye easier, hold brilliant colors longer, and stretch and recover better than other synthetic fibers like nylon and acrylic, and most significantly, PTT fibers resist stains, clean easily, and dry quickly. Yarns made from PTT polymers can combine the most appealing benefits into a single fiber. PTT fiber fabrics not only provide easy care and stretch but also a variety of features such as inherent stain resistance, lasting durability for longer wear, remarkable softness, beautiful fluid drape, and rich brilliant colors. PTT fibers dye at low temperatures, blend with all fibers, and are less expensive, which benefit textile manufacturers as well. Polytrimethylene terephthalate (PTT) is a semicrystalline polymer with many of the same advantages as its polyester cousins, PBT and PET. PTT was first patented in 1941, but commercial production of PTT was not possible until the 1990s, when Shell Chemicals developed a low-cost method of producing high-quality 1,3-propanediol, the starting raw material for PTT. It is the textile and carpet industry’s first significant new material. It gives manufacturers more options for new products than they currently have. Its best property is its stain and static resistances, which are not the result of any additives. PTT fibers feel like wool and perform as well as or better than nylon 6, 6 in carpeting. However, they hold dye much better, which means that manufacturers will have a wider color spectrum to choose from and will be able to produce carpets with long-lasting visual beauty. PTT has slightly more power stretch and recovery than PBT, as well as more than PA 66, PA 6, and PES. Because PBT is so close to PES, it will have the best soft hand of all. Both can be dyed easily at 100 °C and mixed with other fibers. They will be strain-resistant, chlorine-resistant, and resilient.

1.1 Processing The IV of PTT used for fiber applications is 0.80–0.92 dL/g (Mn 16,000–20,000). To avoid hydrolytic degradation, the polymer chips must be dried to a moisture level of 30 ppm prior to melt processing. It is preferable to use a hot-air dryer with a closed loop. PTT is dried for 6 h at 130 °C and a dew point of 40 °C. PTT chips are already semicrystalline after palletizing due to the faster crystallization rate and do

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not require a precrystallization step prior to drying as PET does. The dried polymer is extruded into fibers at 250–265 °C using standard processing machines for bulk continuous filaments (BCF), partially oriented yarn (POY), spin-draw yarn (SDY), and staple fiber [1]. The process of making PTT BCF carpets is detailed in the book by H. H. Chuah et al. The extruded yarn is drawn to a draw ratio of 2.8–3.5 between sets of heated godets. It is then textured with hot air at a pressure of 0.6–1.0 MPa (87–145 psi) and a temperature of 160–220 °C. Heat-setting with steam takes place at 135–145 °C or 175–195 °C when heat-setting with the less effective heat conducting superheated steam. Tufted carpets are dyed in a continuous or batch process with disperse dyes at an atmospheric boil. PTT carpets outperform nylon in walk tests, have a lower static charge of 3.5 kV, and are resistant to coffee, mustard, betadine, red acid dyes, and other stains. PET POY or SDY fiber spinning machines are used to spin PTT POY. In addition to stretch, PTT fabrics have a softer hand and better drape than PET fabrics. PTT fabrics have a desirable dry touch and comfort because they do not absorb moisture like nylon.

1.1.1

Extrusion

Extrusion is a common method used in industry for melting thermoplastic immiscible polymer blends, composites, and nanocomposites. By using high levels of shear at elevated temperatures for extended periods of time, this melt processing method is effective in achieving homogeneous polymer composites. Extrusion procedures for immiscible PTT blends, composites, and nanocomposites differ depending on the material and desired morphology and properties. In all cases, a single-screw or twinscrew extruder (Figs. 1 and 2) with various pressure zones and mixing elements is used. All processing zones have four controlled heating zones: the feed zone, the compression zone, the metering zone, and the die. Temperatures in these zones vary greatly and are empirically adjusted to allow for extrusion. The twin-screw extruder is a machine that consists of two identical co-penetrating and self-cleaning screws set on shafts and rotating in the same direction in a fixed closed casing known as a “barrel.” The twin-screw extruders run indefinitely, with very small dwell times.

1.1.2

Melt Spinning

Melt spinning involves heating polymer until it melts and forms a liquid spinning solution or dope. Chips of polymer are put into a heated hopper. At the bottom, there is a grid (sieve) that only allows molten liquid to pass through. The solution is then filtered to remove impurities. The molten polymer is extruded through a spinneret at high pressure and at a consistent rate into a colder air stream, which solidifies the filaments. Finally, the filament yarn is coiled onto bobbins or processed further for certain desired properties or end-uses. Polyester, nylon, olefin, saran, and glass fibers

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Fig. 1 Single-screw extruder with different zones

Fig. 2 Twin-screw extruder with different feeding zones

are all made via melt spinning as shown in Fig. 3. As a result, it is excellent for the production of PTT fibers.

1.1.3

Wet Spinning

A non-volatile solvent is utilized to turn the raw material into a solution in wet spinning. The solvent is extruded via the spinneret via a chemical reaction between the polymer solution and a reagent in the spinning bath or by simply washing it out. The solvent is eliminated in a liquid coagulation medium after extrusion. Finally, the filament yarn is coiled onto bobbins or processed further for certain desired properties or end-uses. PTT fibers are manufactured by wet spinning (Fig. 4).

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Fig. 3 Melt spinning at different zones

Fig. 4 Wet spinning with different parts and processing

1.2 Characterization PTT has an odd number of methylene units (three) between each of the terephthalates, whereas PBT and PET have even numbers of methylene units. PTT’s physical and chemical structure is influenced by the odd number of methylene units, which gives it extraordinary properties. Because of its unique zigzag structure, PTT has good tensile and stretch recovery characteristics; tensile or compressive forces translate at the molecular level to bond bending and twisting rather than stretching (Fig. 5). PTT’s crystalline regions have a significantly lower modulus than other commercial polymers, such as PET. When forces are removed, a PTT fiber can withstand a significant amount of applied strain (up to 15–20%) and recover completely, i.e., no permanent set) [2].

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Fig. 5 Comparison of stretch recovery

PTT’s glass transition temperature (Tg) is 45–65 °C, and it varies greatly depending on crystallinity and measurement method. It has a melting point (Tm) of 228 °C (depending on sample preparation and annealing time), which is lower than PET’s (265 °C) but close to PBT’s (225 °C) [3]. PTT offers a number of significant advantages in practice. Softness and natural hand are two advantages of PTT-based clothing. PTT is also easy to dye, and the fabric has richer colors and better wash fastness than other fabrics. Furthermore, the PTT fiber is very stain-resistant and does not require any additives or coatings on the surface. It has a higher UV resistance than other fibers and has minimal water absorption and electrostatic charging [4].

2 Major Applications of PTT-Based Polymer Blends, Composites, and Nanocomposites Because of its strain resistance and resilience with basic polyester features, PTT is primarily used as a carpet fiber. However, it is also used in other markets such as textile, films, and engineering thermoplastics. Electrical and electronic connectors, coil forms, plugs, sockets, receptacles, switches, automotive lamp sockets, wire harnesses, sensors, solenoids, motor housings, wiper blades, luggage racks, leaf screens appliance, power tool components, office furniture, and hardware brush filaments are some of the other major applications of PTT and its blends, composites, and nanocomposites [5].

3 Textile Application of PTT-Based Polymer Blends Blending is a simple way to upgrade commodity resins while also tailoring them to specific performance profiles for desired applications. Low production costs, easy development, faster processing, recycling convenience, and tailored properties are

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all advantages of polymer blending [6]. Polymer blending is an effective technique for developing new materials. It is capable of creating materials with properties superior to those of the original polymers. Polymers that are blended with polymers to create high-performance textile materials primarily include crystalline polymers such as Polyethylene terephthalate (PET), Polypropylene (PP), Polybutylene terephthalate (PBT), Polylactic acid (PLA), Polyethylene naphthalate (PEN), Polyolefins, Polyamides, and amorphous polymers such as Polycarbonate (PC), Polyetherimide (PEI), Phenoxy resins/and thermo (EPDM).

3.1 Blends of PTT with PET PTT is a promising material for textile fiber and engineering thermoplastic applications due to its unique combination of properties, both as a neat polymer and in formulated products. PTT in blends, particularly with PET, appears to be an interesting way to reduce costs while retaining some of its advantageous properties. PET fiber is the world’s most abundant and widely used fiber in the textile industry [7]. However, the PTT fiber is a new polyester fiber. PET and PTT have densities of 1.38 and 1.33 g/cm3 , respectively [8]. PTT, in particular, outperforms the other polyesters derived from the homologous series of n-methylene glycols poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) [9]. However, when combined/blended with PET, it exhibits a tailored property (Scheme 1). PET crystallizes slowly, whereas PTT crystallizes easily in the absence of a nucleating agent [10, 11]. As a result, it is anticipated that blending PET and PTT will provide an intriguing way to combine the complementary properties of both polymers. PET/PTT blends were found to be fully miscible in amorphous state using microscopic morphology and thermal transition criteria [12]. The ester-interchange reaction of PET/PTT blends was investigated, and it was discovered that the reaction increases the homogeneity of the blends while decreasing the degree of crystallinity of the melt blends. It was also discovered that adding PET to PTT increases the tensile modulus and tensile strength of PTT/PET blends. PTT/PET blend dyeing properties have also been reported [13].

Scheme 1 Molecular structure of PTT (on left) and PET (on right)

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3.2 Blend of PTT with Polypropylene (PP) Because of their wide applicability and low cost, PP fibers have become one of the largest and fastest growing polymeric fibers [14]. PP fibers have gained popularity in the apparel industry over the last few decades due to benefits such as lower energy consumption in the fiber production process, low price, low density, non-toxicity, durability, good mechanical properties and abrasion resistance, good resistance to many chemicals, and excellent moisture wicking. PP does, however, have some drawbacks, including a lack of a hydrophilic group, poor dyeability, photochemical degradation, and low resilience [15]. The ability of a fiber to recover its original dimensions after being compressed is referred to as resilience. Poor resilience has been observed in the case of a PP fiber-based carpet. Several methods have been used to address the aforementioned drawbacks of PP fibers, including plasma modification, grafting the polymer with other monomers, chemical modification of the fibers, impregnation with nanostructured materials, and blending with other polymers. Among all of these techniques, blending with another polymer appears to be more environmentally friendly, less expensive, and more controllable and thus is more widely accepted and used. Some of the shortcomings have been addressed by combining PP and PTT polymer.

3.3 Blends of PTT with PBT Poly(butylene terephthalate) (PBT) is a semicrystalline polymer with excellent mechanical and processing properties as is well known. As a result, it is commonly used as an engineering thermoplastic material or as a component in blends and copolymers [16]. It was discovered that using organoclay (Cloisite 30B) as nanoreinforcement improved the mechanical properties of nanocomposites when compared to PBT/PTT blends. The tensile modulus of impact-modified PBT/PTT blends improved dramatically with only a 3% organoclay loading [17].

3.4 Blends of PTT with PLA Because of their high specific strength and light weight, plastic materials are widely used in a variety of sectors. General plastic materials, on the other hand, are made from petrochemical resources that are currently depleting and causing environmental difficulties due to their non-biodegradability. As a result, biodegradable plastics are a prospective benefit for environmentally friendly products today. PLA is now available and has shown to be a desirable biodegradable material. It is extremely strong, clear, and biodegradable. PLA, on the other hand, is fragile, which limits its use in the textile sector. PLA has been infused with plasticizers like polyethylene glycol or triacetin

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[18] or blended with polymers like PTT to improve its ductility and flexibility. By combining PLA and PTT, a novel material for textile applications could be created. The addition of PTT to PLA/PTT blends increased PLA crystallization, which improved PLA crystallinity in the blends. When it came to choosing the processing temperature for spinning PLA/PTT blend fiber, the melting characteristics of PLA and PTT in the blends were crucial. It should be highlighted that increasing the PTT content boosted the tensile qualities of the PLA/PTT blends, implying that PLA/PTT blends fiber might be used in the textile sector. At a barrel temperature of 250 °C, S. Padee et al. demonstrated that a PLA/PTT blend with a 90/10 ratio could be melt-spun into fibers [19].

3.5 Blends of PTT with Polystyrene Polystyrene (PS) is a low-cost commodity polymer with special characteristics. PTT/PS blends were thought to be immiscible and incompatible due to the essentially distinct structures of PTT and PS. Reactive compatibilization may be an effective way to improve compatibility in polymer blends with functional groups. A part of the reactive compatibilizer has the opportunity to reside near the interface during melt blending and react with the other component to form graft or block copolymers. As a result, these in situ-formed copolymers tend to anchor and concentrate at the interface, acting as effective immiscible polymer compatibilizers. As a result of the better interface adhesion in the solid state, the performance of a compatibilized blend can be improved. Compatibility of an incompatible blend also usually leads in finer and more stable morphology, better processibility, and improved mechanical qualities.

4 Textile Application of PTT-Based Polymer Composites Fillers, plasticizers, lubricants, stabilizers, modifiers, and other modifying additives (fillers, plasticizers, lubricants, stabilizers, modifiers, and so on) influence the service performance of polymer composites. Thermoplastic polymer matrix composites (PMC) are being developed to replace traditional materials such as glass, aluminum, steel, and concrete in a variety of applications, with several advantages such as processing flexibility and part manufacture. The processing method and form of the final part have a direct impact on its qualities. Pigment, modifiers, fillers, particles, reinforcing agents, and other diverse components are difficult to disperse and distribute within a thermoplastic matrix.

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4.1 PTT/Glass Fiber Composites The adherence of glass fibers in PTT significantly increased the tensile, flexural, and impact capabilities of fiber reinforcement. Glass fiber raises the temperature at which PTT crystallizes and hence has a nucleation impact on PTT. These PTT composites with glass fiber reinforcement have a lot of promise to be employed as a novel engineering material in the car industry, including for external elements. The newly developed glass fiber-reinforced PTT composites can replace/substitute the currently used glass–nylon composite materials. Composite materials with improved stiffness and toughness at the same time have a lot of potential in structural applications. Such composite materials’ high heat distortion temperature, HDT (>220 °C), has great potential in automotive and building product applications [20].

5 Textile Application of PTT-Based Polymer Nanocomposites For more than two decades, polymer nanocomposites have piqued the interest of many research groups due to their unique features that are not shared by traditional composites, principally due to the huge interfacial area per unit volume. They could be thought of as complex systems with two or more phases (continued and dispersed), an explicit separation surface, and at least one nanometer-scale dimension for the scattered component. At least one of the components in polymer nanocomposites is in the form of particles or fibers/films with a diameter of 5–100 nm. The inclusion of a nanofiller into a polymer matrix should result in improved mechanical, barrier, and thermal characteristics, as well as electrically conductive nanocomposites, depending on the type of nanofiller used. The size and shape of nanofiller particles, specific surface area, degree of surface development, surface energy, and the way nanoparticles are distributed spatially in the polymer matrix; all play a role in a considerable improvement in composite qualities.

5.1 PTT/Graphene Nanocomposites Graphene is a two-dimensional, one-atom-thick material made up of sp2 carbon atoms organized in a honeycomb configuration [21]. Graphene is used as a composite in PTT polymer because of its high electron mobility at ambient temperature, outstanding thermal conductivity, and superior mechanical characteristics. Graphene–polymer nanocomposites continue to pique scientists’ and technologists’ curiosity in a variety of domains. When compared to materials like carbon nanotubes, graphene-based nanomaterials have the advantages of other carbon nanofillers, such as electrical and thermal conductivity, while having much lower production costs.

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Furthermore, the enormous specific area of oxidized graphene, along with the huge number of functionalizable chemical groups available for physical and/or chemical interaction with polymers, allows for good dispersion and tunable binding with the surrounding matrix. Electrospinning has gained popularity as a technology for producing polymeric fibers in recent years. Because of their high surface area-to-volume ratio, high porosity, and various nanostructures, electrospun fiber mats have a lot of potential in energy devices, filtration, tissue engineering, and biosensors [22]. Electrospun fibers loaded with GNS or CNT can also improve fiber functional characteristics for advanced applications [23].

5.2 PTT/CNT Nanocomposites CNT is an intriguing antistatic agent because of its unique electrical properties. Depending on the orientation of its hexagonal structure, it can have conductive behavior similar to metal. CNT has electrical characteristics that are important for improving the electrical conductivity of polymers, and CNT/polymer composites have been studied from the first studies in this field [24]. Furthermore, because to their low density, outstanding thermal properties, and good mechanical qualities such as high stiffness, tensile strength, and high elongation at break, CNTs are widely used in engineering applications. Following Ijima’s [25] discovery of the carbon nanotube (CNT), a great deal of effort has gone into determining the best features of carbon nanotubes. PTT/MWCNT composites were explored by Wu [26]. For the PTT grafted with acrylic acid, the hydroxyl-functionalized CNT acts as anchoring sites. MWCNT’s compatibility and dispersibility in the matrix of PTT are improved by functionalization. The thermal and mechanical properties of functionalized MWCNT have significantly improved, leading to the conclusion that they can be employed to make high-performance PTT nanocomposites.

5.3 PTT/Clay Nanocomposites Nanoparticles can be three-dimensional (nanogranules, nanocrystals, and spherical nanoparticles like SiO2 and TiO2 ), two-dimensional (clay), or one-dimensional (carbon nanotubes) in size [27]. Clays are frequently incompatible and difficult to disperse in a polymer matrix. As a result, the organic alteration of the clay’s surface by a specific organic surfactant has been used to aid in its dispersion [28]. Clay platelets in exfoliated nanocomposites have also been found to operate as an effective nucleating agent, increasing crystallinity and crystallization rate. Various intercalation processes, such as solution, melt, and in situ polymerization, were used to create these nanocomposites.

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6 Conclusion Because of a recent breakthrough in lower-cost monomer synthesis, PTT is a polymer that has rekindled interest. It belongs to the aromatic polyester’s family, which includes PET and PBT. PTT offers a wide range of performance characteristics, making it a viable candidate for engineering thermoplastic applications. It combines the strength, stiffness, and high heat deflection temperatures of PET with the wide processing window of PBT, expanding the range of applications for already versatile polyesters. PTT has incredible properties for textile applications when reinforced with various polymers, fillers, and nanofillers. Acknowledgements The authors wish to acknowledge the funding of Dept. of Chemicals & fertilizers, Govt. of India under the scheme of establishing, Center of Excellence (CoE) and support of the Laboratory for Advanced Research in Polymeric Materials (LARPM), School for advanced Research in Petrochemicals (SARP), Central Institute of Petrochemicals Engineering and Technology (CIPET), Bhubaneswar, India, that made this study possible.

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Chapter 13

Antistatic Packaging for Electronic Devices of PTT-Based Polymer Blends, Composites, and Nanocomposites Natália Ferreira Braga , Thais Ferreira da Silva , Erick Gabriel Ribeiro dos Anjos , Henrique Morales Zaggo, Yves Nicolau Wearn , Eduardo Antonelli , and Fabio Roberto Passador

List of Abbreviations ABS AC AR CB CNT CCVD DS

Acrylonitrile butadiene styrene Alternating current Aspect ratio Carbon black Carbon nanotubes Chemical catalytic vapor deposition Dielectric spectroscopy

N. F. Braga (B) · T. F. da Silva · E. G. R. dos Anjos · H. M. Zaggo · Y. N. Wearn · F. R. Passador (B) Polymer and Biopolymer Technology Laboratory (TecPBio), Federal University of São Paulo (UNIFESP), 330 Talim St., Zip Code 12231-280, São José Dos Campos, Brazil e-mail: [email protected] F. R. Passador e-mail: [email protected] T. F. da Silva e-mail: [email protected] E. G. R. dos Anjos e-mail: [email protected] H. M. Zaggo e-mail: [email protected] Y. N. Wearn e-mail: [email protected] E. Antonelli Advanced Ceramic Laboratory, Federal University of São Paulo (UNIFESP), 330 Talim St., Zip Code 12231-280, São José Dos Campos, Brazil e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. R. Ajitha and S. Thomas (eds.), Poly Trimethylene Terephthalate, Materials Horizons: From Nature to Nanomaterials, https://doi.org/10.1007/978-981-19-7303-1_13

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DWCNT ESD EG EMI-SE EPT f-MWCNT GC GIC GNP HDPE LDPE MIL-STD MWCNT PTT PTT-g-MA rGO SR SWCNT VR 2D 3D 1D 0D

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Double-wall carbon nanotubes Electrostatic discharge Exfoliated graphite Electromagnetic interference shield Electrical percolation threshold Functionalized MWCNT Glassy carbon Graphite/graphene-intercalated compounds Graphite/graphene nanoplatelets High-density polyethylene Low-density polyethylene Military Standard Multiwall carbon nanotubes Poly(trimethylene terephthalate) Maleic anhydride-grafted PTT Reduced graphene/graphite oxide Surface resistivity Single-wall carbon nanotubes Volume resistivity Two-dimensional Tridimensional One-dimensional Zero-dimensional

List of Symbols σ ρ θ ω ε* f i M* V Y* Z Z* Z’ Z"

Electrical conductivity Electrical resistivity Phase difference between the voltage and the electrical current Angular frequency Complex permittivity Frequency Electrical current Electric modulus Electrical potential Admittance Real impedance Complex impedance Real part of complex impedance Imaginary part of complex impedance

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1 Introduction Polymer composites are a class of materials that have been emerging in various fields of applications due to their exceptional properties. More specifically, the electrically conductive polymer composites have a great interest in electromagnetic interference shield (EMI-SE) materials [1–3], radar absorption [4, 5], electrochemical capacitive energy storage [6, 7], and antistatic packaging [8–11]. Conductive polymer composites are composed of an insulating polymer matrix with the addition of a conductive filler, as carbon-based materials, and can also be named extrinsically conductivity composites [12–14]. Conductive polymer composites can be a great alternative material to produce packaging for electronic components and devices, which typically is derived from an existing packaging, but with the additional protection against electrostatic discharge (ESD). ESD is the transfer of an electrostatic charge between bodies to different potentials and occurs with direct contact or when induced by an electrostatic field. ESD is particularly very dangerous for electronic components where a voltage greater than that supported by the components can destroy them. Consequently, electronic components and devices should be transported and stored in antistatic packaging [9, 15]. Poly(trimethylene terephthalate) (PTT) is widely used for the physical protection and packaging of several products. PTT is an engineered thermoplastic semicrystalline polyester with high-quality properties. Among the various engineering thermoplastics, PTT has aroused great interest due to its versatile properties and good potential for various applications [16]. PTT is known for its tensile strength, elastic recovery, surface properties, chemical and abrasion resistance, dimensional stability, and crystallization rate [17]. However, the fragile nature of PTT can limit its applications [18, 19]. Therefore, through blends of PTT with other polymers such as acrylonitrile butadiene styrene (ABS) [20], high-performance material with desired properties for packaging applications can be expected. As an insulating polymer, PTT accumulates static electricity which can cause serious damage to electronic components. Therefore, antistatic agents such as carbon nanotubes (CNT), graphite, and graphene nanoplatelets can be added to PTT to decrease the static electricity, making the polymer more electrically conductive [9, 21, 22]. When a conductive material is added to the PTT, an ESD shield is created. This shield has a low electrical charge, and the packaging can shield ESD-sensitive electronic components and electrical charges from other sources [8, 15]. However, the addition of another polymeric phase and/or the addition of a conductive filler in the PTT matrix is not easy, due to the compatibility between these materials. The compatibility between the components is of great importance and influences the final properties of the polymer blends and nanocomposites and the interfacial region where the transfer of deformations from the matrix to the reinforcement agent occurs. To solve this problem, the use of compatibilizer agents such as maleic anhydride-grafted PTT (PTT-g-MA) is required [23].

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Therefore, this chapter aims to present the use of antistatic agents such as CNT, graphite, and graphene nanoplatelets in the PTT matrix for application in antistatic packaging for electronic devices. Also, it describes the modification of the filler in PTT-based nanocomposites, such as multiwall carbon nanotubes’ (MWCNT) chemical functionalization; the use of compatibilizer agent, such as PTT-g-MA; and the addition of a second phase (ABS) for the development of a polymer blend based on PTT for application in antistatic packaging.

1.1 Antistatic Packaging Packaging is a container or wrapping that temporarily stores products, individually or grouped into units, whose main function is to protect and preserve the quality of the most diverse products during their distribution, storage, and marketing and to ensure the effective satisfaction of the final needs of the consumer [24]. The use of an efficient and suitable package is especially important in the electronic industry since printed circuit boards and general electronic components are sensitive to ESD [24]. ESD is a natural phenomenon that consists in the transfer of charges between two bodies that are in different electric potentials. ESD, in addition to being able to cause electrical shock, can produce electromagnetic interference, degrade the performance of the device, or even damage sensitive electronic components [15]. The appearance of ESD can result from the imbalance of charges generated by friction between objects of certain types of materials, especially those with a high surface electrical resistance. The phenomenon by which a given material loses or gains charges and creates electrostatic voltages on other objects. The tendency of material with charge imbalance is to return to electrostatic equilibrium. During the return to equilibrium, the charge flow generates an electrical discharge with a very short duration [15]. Therefore, the storage of sensitive devices or components should never be done in common plastic bags and boxes that have as an intrinsic characteristic the accumulation of electrical charges potentially generating electrostatic discharges. The correct way to store a susceptible object is to use antistatic packaging, which is properly prepared to dissipate electrical charges [8, 15]. Polymeric matrices are the best alternatives to produce antistatic packaging, considering their inherent lightness and good processability. However, most polymers are insulating materials, so it is necessary to modify their formulation to impart dissipative properties to their structures [15]. There are currently several semiconductor polymers, such as polyaniline and polypyrrole, which can be an alternative to produce antistatic packaging, as they have low electrical resistivity. However, the processing of these materials in conventional thermoplastic transformation equipment is complex and may make the process of obtaining packaging unfeasible [8]. Another alternative is the addition of functional fillers, which are called antistatic agents or additives. Among the carbon materials used as antistatic agents, it is possible

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Fig. 1 Electrical resistivity classification [Source Author]

to mention CNT [20], carbon black (CB) [15, 25], glassy carbon (GC) [26], graphene [27], and graphite/graphene nanoplatelets (GNP) [28]. Materials used for packaging production can be classified according to their electrical resistivity into electrically conductive materials and dissipative materials as shown in Fig. 1. Conductive materials can have conductive surface and/or conductive volume. A conductive surface and/or volume material must have an electrical resistivity less than 1 × 104 Ω/sq. Within the classification of conductive materials, some materials are considered as shielding, as they have a surface and/or volume resistivity smaller than 1 × 103 Ω/sq. Dissipative materials must have a surface or volume resistance greater than or equal to 1 × 104 Ω/sq, but less than 1 × 1011 Ω/sq. Insulating materials must have a surface or volume resistance greater than or equal to 1 × 1011 Ω/sq [29]. Therefore, antistatic packaging protects the electronic device not only against physical and environmental damage but also against electrostatic discharge [8, 25]. Antistatic packaging must have an electrical resistivity low enough to dissipate electrical charges through its structure [10, 30]. Antistatic materials have electrical resistivity in the range of 103 –1010 Ω/sq [30, 31].

2 Antistatic Agents The US Military Standard (MIL-STD) divides electrostatic discharge protective packaging into three types that are generally used for other areas, as follows: Type I are packings with metallic and polymeric films in a laminated structure that dissipates ESD by a Faraday cage principle; Type II are polymers filled with antistatic agents, which are dispersed in the polymer matrix to create a threshold percolation path to dissipate charges; and Type III are polymer matrix with a vapor-deposited metallic layer in that surface, also applying the same dissipating principle than Type I. Here, we focus on Type II ESD protective packing [32]. Generally, antistatic agents are electrically conductive fillers that, when added at a particular concentration inside the insulator polymer matrix, might form a path for dissipating the electrostatic charge. The most industrial-used antistatic agent is carbon black (CB). CB is an abundant and low-cost carbon-based material with a complex structure based on sp2 carbon in the form of hexagons with functional groups

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at its edges. The three-dimensional morphology of CB consists of spherical primary particles that form aggregates, and then, these aggregates form agglomerates [24]. Nonetheless, high contents of CB are necessary to reduce the electrical resistivity of the matrix, around 10–20 wt%, and the composite processing has some difficulties, associated with its breathing toxicity and high dispersion of CB in the air. Thus, the substitution of CB by other carbon-based materials is promising to overcome those limitations. As a consequence of the allotropy phenomenon presented by the carbon element, the existence of a wide range of carbon materials, containing specific properties, becomes an advantage for many industrial sectors as it allows the development of a great variety of products with unique characteristics and applications [33]. Allotropy is exactly the particularity of some elements to be encountered organized in distinct crystalline structures depending on their formation parameters [33, 34]. When it comes to carbon, this phenomenon is responsible for the atomic arrangement of different materials with potential use as antistatic agents in antistatic packaging manufacture [24]. Thus, for the understanding of how these carbon fillers act as antistatic agents in a polymer matrix, the current topic sets the main characteristics and properties of some of these materials.

2.1 Graphite The several forms of carbon allotropes cannot be supported just by the electronic configuration of a carbon atom. However, due to the low energy gap between 2 s and 2p orbitals, electron promotions enable different orbital hybridizations which explain these variabilities of structures [35]. As one of the carbon allotropes, graphite has a crystalline structure based on sp2 hybridized carbon atoms covalently bonded forming planar layers constituted by hexagonal rings. In this configuration, the p orbitals remaining in each atom are perpendicularly disposed of in relation to the plan, being responsible for the van der Waals interactions between adjacent layers, distancing them in approximately 3.35 Å (Fig. 2). Then, these bonds are longer, but weaker, than the C–C bonds within the layers, assigning to graphite its softness and lubricating character [24, 33, 35]. Moreover, this difference between bonding forces leads to the anisotropy of graphite [33]. Sequentially, the effects of anisotropy on some important properties of graphite for its application in antistatic packaging are summarized. With Young’s modulus around 1 TPa within the plan as a result of the strongly bonded carbon atoms, the weak van der Waals interactions in the perpendicular direction cause a significant reduction of the elastic modulus (around 36 GPa) [15, 33, 36]. Furthermore, for synthetic graphite, tensile strengths’ measurements are of about 100 GPa and 30 GPa in parallel and perpendicular directions, respectively [36]. About the thermal properties, in the parallel direction, graphite presents a thermal conductivity of approximately 390 W/m·K, a low coefficient of thermal expansion, and good chemical stability under high temperatures and non-oxidizing atmospheres

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Fig. 2 Scheme of graphite structure [Source Author]

[33, 36]. Finally, for its electrical properties, the graphene layers in the tridimensional structure are sufficiently spaced in a way that has difficult electron movement mechanisms. Consequently, the electrical resistivity observed within the plan (2.5–5.0 µΩ·m) is much lower when compared to the one within the plane (3000 µΩ·m) [33]. In addition to the possibility of being directly applied as an antistatic agent in polymeric composites [15, 37], graphite can also be submitted to some structure manipulating methods to obtain other graphitic materials with antistatic application interests [24, 35]. As well as graphite, the structure of these materials is mostly composed of sp2 hybridized carbon atoms [24]. On the other hand, because of the non-maintenance of the crystallographic order in the direction perpendicular to the plan, their properties differ from graphite, allowing different applications [33]. Considering the antistatic polymeric composites’ production, some graphitic materials already cited as promising functional fillers include reduced graphene/graphite oxide (rGO), exfoliated graphite (EG), graphite/graphene-intercalated compounds (GIC), and graphene/graphite nanoplatelets (GNP) [24]. This last one will be more detailed in sequence.

2.2 Graphene Nanoplatelets As one of the carbon allotropes, the graphene structure atoms are distributed in the form of a two-dimensional (2D) monolayer consisting of a hexagonal structure of sp2 carbon hybridization, with a C–C distance of approximately 1.42 Å. Considered the thinnest material of the universe—a layer thickness of 0.34 nm—the structure of a graphene sheet can be rolled up to form the fullerenes (0D), rolled on its axis to form the carbon nanotubes (1D), or stacked on itself to form the tridimensional structure of the graphite (3D) [38].

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Fig. 3 Representation of the structure of the single-layer graphene (left) and graphene nanoplatelets (GNP) (right) [Source Author]

Graphene nanoplatelets (GNP) are some of the graphene-based materials that have been commercially attractive, with an average thickness of 5–10 nm that, due to having a not very high number of layers, exhibit some of the graphitic properties to be found in the single-sheet graphene [39, 40]. The representation of the structure of both single-layer graphene and GNP is shown in Fig. 3. As for the other carbon fillers, the main advantages that make the GNP available for practical uses include high thermal conductivity (5300 W/m.K) and remarkable and unique electrical and electronic properties (electrical conductivity of ~ 108 S/m). Due to its high aspect ratio (as high as 250), the graphene-based materials provide elevated surface area, flexibility, transparency, and strong mechanical properties (theoretical Young’s modulus of 1 TPa and intrinsic strength of 130 GPa) [24, 39]. The considerable low cost also makes the GNP feasible for polymer composites regarding its dissipative properties [24].

2.3 Carbon Nanotubes Carbon nanotubes (CNT) are one-dimensional nanomaterials and another carbon sp2 allotrope. More straightforwardly, the CNT are rolled graphene sheets, and their properties vary according to the configuration, number of walls, diameter, length, and the presence of defects [41]. These 1D nanomaterials present outstanding mechanical resistance, thermal, and electrical conductivity in its axis direction, being highlighted as a candidate to improve polymer matrices’ properties in nanocomposites [42]. The rolling direction generates three different configurations for CNT: Armchair, zigzag, and chiral, as shown in Fig. 4. Each configuration might confer a semiconductor or a conductor electrical behavior: For armchair CNT, the n and m indexes are equal, which results in metallic electrical conductivity for these CNT; zigzag CNT could be semiconductors for n indexes different from 3 and its multiples, being conductor otherwise; and finally, the chiral CNT are conducted in specific configurations when the difference between n and m indexes is a 3 multiple [43, 44]. The number 3 is related to the number of carbon atoms necessary to generate a perfect

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Fig. 4 Carbon nanotubes: Different configurations and number of walls [Source Author]

hexagon structure, allowing electrical conductivity. When that condition is not satisfied, the CNT structure may present pentagons and other imperfect structures that are not conducive and act as defects, generating CNT semiconductors [44]. The distance between walls in CNT is 3.36 Å [43], similar to the graphene planes in graphite. From the number of walls, CNT can be classified as single-wall (SWCNT), double-wall (DWCNT), and multiwall (MWCNT). Each number of walls contributes differently to the CNT properties in nanocomposites. SWCNT provides excellent mechanical properties due to its high surface area and small diameters. On the other hand, MWCNT preserves the MWCNT electrical characteristics of CNT once the external walls shield the internal walls and bypass some structural defects that could be caused by processing or CNT functionalization [45, 46]. Finally, the DWCNT balances the properties of both types. However, as SWCNT, it is challenging to produce and has a higher cost than MWCNT [42, 46].

3 Superficial and Volumetric Electrical Resistivity In general terms, the electrical resistivity (ρ) of a material quantifies how much that material resists the flow of electricity. A material has low electrical resistivity if the electricity flows easily through the sample; otherwise, if the electricity flows difficult, the material has high resistivity [47]. The inverse of electrical resistivity is the electrical conductivity (σ) (Eq. 1), and the higher the resistivity, the less conductive the material is. But both can be used for illustrating the electrical properties of materials. The most usual test methods to determine polymeric sample resistivity are ASTM D257 [48] and IEC 62,631–3-1 [49]. σ = 1/ρ

(1)

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The electrical resistivity is an intrinsic physical property of a material, and it is different for each class of material: Plastics commonly are electrically insulating, and metals are conductors. So, electrical resistivity depends on the type of material, and this concept is different from the term “resistance,” which is the capacity of a material to oppose the flow of an electrical current and its dependents on how much of material is present [50]. The most common types of resistance measurements are [50]: • Volume resistivity (VR), also known as bulk resistivity. • Surface resistivity (SR), also called sheet resistance. The VR is the measurement of resistivity perpendicular through the plane of the sample; in this case, the electron passes through the sample. In this method, the electrodes are in contact with both sides of the material [50], as shown in the scheme of Fig. 5. VR is measured in units: ohm·meter (Ω·m) or ohm·centimeter (Ω·cm). The volume conductivity is measured in (1/(Ω·cm)), that is Siemens/centimeter (S/cm), or (1/(Ω·m)) that is S/m. Whereas the SR is related to the measurement of the resistivity along the surface of the material, the current is along the plane of the sheet, as schematically presented in Fig. 5. This method is often used for coatings or thin films, with uniform thickness, and it is independent of the thickness of the sample [47, 50]. The term “sheet resistance” has shown up in defining materials to control EDS [51]. The SR is measured in units: ohm/square (Ω/sq), which is dimensionally equal to an ohm (Ω) [52], but it cannot be misinterpreted: The unit “sq” means meter/meter (m/m) or (cm/cm), and it was established only to not make confusions with Ω from resistance. The relation between VR and SR is that SR multiplied times the thickness of the sample is equal to the VR.

Fig. 5 Methods to measure volume resistivity and surface resistivity of a sample [Source Author]

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The most common experimental techniques used for measuring electrical resistivity are the two-probe method and four-probe method, the last, more specifically for SR [47, 50, 53]. The two-point technique measures the resistivity of material using two electrical contacts placed on opposite faces of the sample. It is a simple method, and it is possible to use a multimeter to measure the resistance [50]. On the other hand, the four-point technique uses four electrical contacts on the surface of the sample [47]; in this case, a current passes through the outer probes and induces a voltage in the inner voltage probes. Another important technique for measuring the volume electrical resistivity that will be discussed in this chapter is the dielectric spectroscopy (DS) also known as impedance spectroscopy or electrochemical impedance spectroscopy.

3.1 Dielectric Spectroscopy Dielectric spectroscopy (DS) is an essential tool for the characterization of materials of physical, chemical, and biological applications [54]. There has been an increasing interest in developing polymers and composites with different electrical properties and applications, and in this context, the DS is of great importance for their characterizations. DS technique measures and analyzes the behavior of the samples’ physical properties as a function of the time while they are exposed to a frequency-dependent external electric field. The experimental apparatus for DS is relatively simple; the measurements are quick and do not require complex sample preparation. The obtained data can be expressed and analyzed using different formalisms. In terms of impedance, when an electrical potential V(t) = V m sen(ωt) at a frequency f = ω/2π is applied to a sample, it responds with an electrical current, i(t) = I m sen(ωt + θ ), where θ is the phase difference between the voltage and the electrical current and ω is the angular frequency. Then, the impedance is defined as being Z*(ω) = V(t)/i(t). The concept of impedance is more general than electrical resistance once impedance considers the shift between the stimulus and the system’s response. The complex impedance can be expressed as Z*(ω) = Z’ + iZ”, and in a graphical representation, the real part (Z’) is represented on the x-axis and the imaginary part (Z”) is represented √ on the y axis. The complex number is equal to i ≡ −1 ≡ exp(i π/2) and indicates a counterclockwise rotation of π/2 to the x-axis [55]. Impedance is, by definition, a complex quantity and frequency-dependent. However, when θ = 0, the impedance presents only resistivity behavior and Z(ω) = Z’(ω) [55]. In general, in DS, the experimental data are analyzed using complex formalisms as impedance (Z*(ω) = Z’ + iZ”), admittance (Y * (ω) = Z *−1 = Y’ + iY”), electric modulus (M*(ω) = iωCoZ*), complex permittivity (ε* (ω) = 1/iωC o Z*(ω)), and the conductivity (σ*(ω) = iωε*) [55]. The most evident way to analyze the DS is to directly obtain the conductivity, permittivity, or capacitance data as a function of the composition, sample preparation method, or even the temperature when the DS equipment is coupled to a furnace. Nevertheless, DS allows us also to analyze and interpret the results using the real

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and imaginary parts, such as capacitance and permittivity. Besides, the application of different formalisms is helpful for the interpretation of dielectric spectra, especially when there is the superposition of different polarization or conduction mechanisms [54]. Significant for the understanding of DS data are the considerations of Debye [56], who describe the behavior of polarization of materials when subjected to an external electric field. Debye considered non-interacting dipoles floating in a viscous medium that led to the time dependence of the dielectric polarization, P(t) = P0 exp(t/τ), where τ is the relaxation time. Experimental impedance data can also be analyzed in terms of equivalent circuits that simulate the response of the real material. For example, a dielectric material exhibits a response that is neither purely resistive nor purely capacitive. Instead, in a simplification, it can be physically approximated as an association of a resistor and capacitor connected in parallel. For a composite material or material with different phases and compositions, the experimental impedance response can be approximated for a parallel combination of resistors and capacitors connected in series. This methodology allows separating the contribution, for example, of each component of a composite material. Thus, we link the microstructural characteristics of the material and its electrical properties.

3.2 Anisotropy in Nanocomposites’ Electrical Properties Many factors influence the electrical properties of nanocomposites that might be associated with the filler, the matrix, and the processing conditions [15]. The processes to prepare nanocomposites are generally divided into solution mixing, in situ polymerization, and melt mixing. The last one is the most used and preferable from an industrial point of view, allowing high productivity and being solvent-free [43]. Although many of the melt-mixing processes, like the extrusion process, involve high shear rates and are not so efficient as solution mixing and in situ polymerization to achieve high electrical properties in a lower content, which is associated with a well-dispersed and distributed nanofillers’ morphology [15]. The industry’s most traditional melt-mixing processing to prepare thermoplasticbased products is injection molding, which involves elevating shear rates (≥ 105 s−1 ) and longitudinal flow that generates a skin–core morphology. That morphology and those factors might lead to an anisotropic electrical behavior for thermoplastic-based nanocomposites processing by injection molding [57, 58]. In addition, MWCNT and GNP may be inducted to orient in the longitudinal flow direction due to the shape and nanosize of these fillers. Consequently, the injection-mold flow direction is more likely to present a high electrical conductivity for a low content of these rather than the other direction [57, 58]. Processing conditions as mold temperature might attenuate this behavior; moreover, the anisotropy in electrical properties for nanocomposites in those conditions must be considered in the production of rigid antistatic packing, for example.

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4 Experimental 4.1 Materials PTT: Poly(trimethylene terephthalate): Corterra 200 (Montreal, QC, Canada), supplied by Shell Chemicals, with a density of 1.35 g/cm3 . ABS: Acrylonitrile butadiene styrene: MG38—Cycolac, supplied by SABIC Innovative Plastics (Riyadh, Saudi Arabia), with a density of 1.04 g/cm3 . PTT-g-MA: Compatibilizer agent maleic anhydride-grafted PTT was produced by reactive extrusion of PTT (96 wt%) with benzoyl peroxide (2 wt%) and maleic anhydride (2 wt%) [23]. MWCNT: Multiwall carbon nanotubes: Nanocyl SA-NC7000 with a minimum purity of 90% and average diameter and length of 9.5 mm and 1.5 um, respectively, produced by the chemical catalytic vapor deposition (CCVD) process. f-MWCNT: Functionalized MWCNT was produced through a chemical treatment by oxidation with nitric acid solution (HNO3 6.0 mol.L-1 ), according to the methodology reported by [9, 59]. Graphite: As residual components supplied by companies of the aerospace sector. GNP: Graphene nanoplatelets: CheapTubes with 97% of purity, average thickness of 8–15 nm, lateral size dimension of >2 um, and specific surface area of 500–700 m2 /g. The GNP were produced by chemical exfoliation of natural graphite.

4.2 Composites Preparation The different composites and nanocomposites’ compositions were prepared using an AX Plastics co-rotational twin-screw extruder, followed by the molding of thin films (thickness of 150 um) using a hydropneumatic press. The preparation conditions are described and illustrated in Fig. 6.

4.3 Electrical Characterization The electrical conductivity (σ) of the samples was performed by impedance spectroscopy and electrical resistivity AC (alternating current). The values of σ were calculated by the inverse of the electrical resistivity (ρ) according to Eq. (1), as ρ was determined by Eq. (2). ρ = (Z .A)/t f ilm

(2)

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Fig. 6 Scheme of the preparation of the composites and nanocomposites by extrusion and molding processing [Source Author]

where Z is the real impedance, A is the electrical contact area, and tfilm is the thickness of the film samples. Through this characterization, a thin layer of gold/palladium alloy was deposited using a sputter coater on both sides of the samples to form an electrical contact, producing a metal–nanocomposite–metal structure. Impedance measures were determined on an impedance analyzer (Solartron SI 1260, Impedance/Gain-Phase Analyzer). The measurements were performed at room temperature at a frequency of 10 Hz and voltage amplitude of 0.5 V.

5 Results and Discussions 5.1 Effect of the Aspect Ratio of the Antistatic Agent on the Electrical Properties of PTT Composites The aspect ratio (AR) of the filler is considered to be one factor that can interfere with the electrical percolation threshold (EPT) of conductive polymer composites. The AR is defined as the ratio between the longest and smallest dimensions of a particle [15]. In conductive polymer composites, the increase in filler content into the matrix gradually forms a conductive path, and generally, low values of EPT are reached in composites with particles with high AR. The phenomenon of electrical percolation is the critical filler concentration reached to form a conductive pathway [60].

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Fig. 7 Scheme of comparative aspect ratio between graphite, graphene nanoplatelets (GNP), and CNT [Source Author]

Graphite, graphene, and MWCNT are carbon-based materials, with excellent intrinsic physical properties, but with different shapes and AR. Graphite is a threedimensional (3D) material, formed by a stack of many layers of graphene. Graphene is two-dimensional (2D) one sheet of graphene, and MWCNT is one-dimensional (1D) filler; it is a roll of graphene sheet into a cylinder, thus having the highest AR, as shown in Fig. 7. Although these materials share similar properties, each one has unique uses and specific applications. The effect of these three different fillers on the electrical resistivity of PTT systems (PTT/MWCNT, PTT/graphite, and PTT/graphene) was investigated and shown in Fig. 8. The PTT is an insulating polymer with high electrical resistivity, varying from 1010 to 1012 Ω.cm. The filler is considered a critical factor to decide the properties of a polymer composite material. Polymer composites with macrofiller, like graphite, generally need high filler concentration: In composite PTT/graphite, a sharp decrease in electrical resistivity occurs with 10 wt% of graphite; from this concentration, the material changes its behavior from insulator to conductor. Krupa et al. [61] found a percolation concentration of 11 vol.% of graphite in both low-density polyethylene (LDPE) and high-density polyethylene (HDPE) matrices, characterized by a sharp increase in the electric conductivity of the composites. The graphite particles form clusters that penetrate throughout the polymer matrix forming a conductive way for the transport of electrons on the sample. The PTT/MWCNT nanocomposites exhibit a sharp decrease in electrical conductivity at significantly lower filler content, and the EPT occurs at only 0.5 wt% of filler. It was observed a reduction in eight orders of magnitude. The conductive network is more easily formed in the MWCNT system, than in graphene or graphite, because MWCNT has a high aspect ratio, permitting the electron flow easily throughout the composite. Like the PTT/MWCNT nanocomposite, the graphene nanoplatelets can also form conductive pathways when exceeding the EPT. However, to achieve similar values of electrical resistivity, more graphene is needed than MWCNT, which can be explained by the difference in the structure and aspect ratio of these materials. Graphene nanoplatelets are flexible and tend to fold into complex structures with more boundaries, while CNT are rigid structures and can easily form networked paths at much

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Fig. 8 Electrical resistivity of PTT systems with different carbon-based fillers. *It was not possible to achieve EPT in PTT/graphene at this filler content; however, according to Huang et al. [62], experimental values of EPT are 6.1 vol% for their composites of PTT/GNS; and the electron conductive pathway in three different systems [Source Author]

less filler content [60]. The good dispersion of the graphene nanoplatelets on the polymer matrix is crucial to guarantee improvement of the physical properties of the composite. The filler alignment is important to improve electrical conductivity by several orders of magnitude. Due to their 1D structure, CNT can easily align by external forces as mechanical stretching, electrical or magnetic fields. However, the alignment of graphene nanoplatelets is still a challenge [60]. In Fig. 8, it is possible to observe that the EPT was not reached at 2.5 wt% of graphene, indicating that this filler content is not enough to form a conductive pathway for electron transport. However, it is possible to find in the literature some works which report the electrical conductivity of PTT/graphene nanocomposites. Huang et al. [62] prepared PTT/GNP by electrospun and investigated the electrical properties. The authors found that the experimental filler volume fraction for EPT is 6.1 vol.% of GNP; also, an increase of nine orders of magnitude was observed from neat PTT to PTT/GNP with 7.35 vol% of GNP. Considering the performance of polymer composites, this discrepancy on EPT of the PTT systems can be attributed to other aspects and should be considered, besides the AR, the state of filler dispersion, geometric structure, and surface area [63].

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5.2 Effect of Adding a Compatibilizer Agent on the Electrical Properties of PTT Composites Maleic anhydride grafted with PTT (PTT-g-MA) is a compatibilizer agent for PTTbased composites and nanocomposites and can influence the electrical properties of the composites. The PTT-g-MA was prepared by reactive extrusion using a mixture of PTT, MA, and benzoyl peroxide (BPO), as described by Braga et al. [23]. The compatibilizer agent aims to improve compatibility and adhesion of the filler on the PTT matrix, promoted by the presence of functional groups improving the overall properties of the composite [23]. The influence of the addition of 1, 5, 10, and 20 wt% of graphite, with 0.5, 2.5, 5, and 10 wt% of PTT-g-MA, respectively, on the electrical properties of PTT/PTTg-MA/graphite composites was verified. Also, it investigated the addition of 0.5 and 1 wt% of MWCNT on the properties of PTT/PTT-g-MA/MWCNT nanocomposites compatibilized with a fixed concentration of 3 wt% of PTT-g-MA (Fig. 9). It is observed that the EPT was reached with only 0.5% wt% of MWCNT in composite PTT/PTT-g-MA/MWCNT, as occurred in the non-compatibilized composite of PTT/MWCNT (Fig. 8). So, in this system, the compatibilizer agent did not influence on the transport of electrons in the sample, consequently on the electrical properties of PTT composite. On the other hand, it was discussed that the EPT of the non-compatibilized PTT/graphite was 10 wt% (as presented in Fig. 8), and it is possible to see that the same filler content in the compatibilized composite PTT/PTT-g-MA/graphite was not

Fig. 9 Electrical resistivity of PTT/PTT-g-MA/MWCNT and PTT/PTT-g-MA/graphite: effect of the compatibilizer agent [Source Author]

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enough to form the conductive path because the composite presented high electrical resistivity, in order of 109 Ω.cm. One hypothesis is that the addition of the compatibilizer agent reduces the amount of graphite agglomerates in the matrix, dispersing the graphite throughout the material. As the aspect ratio is much smaller compared to CNT and the good dispersion caused by the compatibilizer agent, a larger amount of graphite was necessary to increase the probability of graphite creating a path for electrical percolation to occur. The electrical resistivity of PTT/PTT-g-MA/graphite with 20 wt% (70/10/20) considerably decreased eight orders of magnitude compared to PTT. According to Pang et al. [64], the materials for antistatic applications require an electrical resistivity in the range of 106 –1011 Ω.cm, and conductive polymer composites’ materials with electrical resistivity from 10 to 106 Ω.cm are classified as conductive, so being considered both relevant for ESD protection packaging and for EMI-SE.

5.3 Effect of a Second Phase Addition on the Electrical Properties of PTT/ABS Blend-Based Carbon Nanotubes’ Nanocomposites Figure 10 compares the electrical resistivity of three different PTT/ABS blends’ ratios, all of them compatibilized with 3 wt% of PTT-g-MA, with two contents of MWCNT (0.5 and 1 wt%) to investigate the effect of the addition of a second phase on electrical properties of PTT.

Fig. 10 Electrical resistivity of PTT/ABS blends with different contents of ABS and MWCNT (left) and the electrical percolation path in PTT/ABS blends (right) [Source author]

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As it is possible to observe that the PTT/ABS blends are electrically insulating and present high electrical resistivity, in order of 1010 Ω.cm. In the three cases, it is evident that the electrical resistivity sharply decreases with the addition of low content of MWCNT (0.5 wt%). For example, the volume resistivity of PTT/ABS80/20 is 8.4 × 1010 Ω.cm and decreased to 5 × 102 Ω.cm when 0.5 wt% of MWCNT was added. This phenomenon of rapidly decreasing, ~ eight orders of magnitude, in electrical resistivity is well known as percolation threshold, the minimum content of filler to form an interconnect structure of MWCNT in the polymer matrix. The nanocomposites of PTT/ABS-60/40 with 0.5 wt % and 1 wt% of MWCNT presented electrical conductivity in order of 103 Ω.cm and 102 Ω.cm, reduction of seven orders and eight orders of magnitude, respectively. However, it is possible to observe that the blend-based CNT nanocomposite with a higher concentration of ABS (PTT/ABS-40/60) presented the highest values of electrical resistivity compared to the blend-based CNT nanocomposites of PTT/ABS80/20 and 60/40. The electrical resistivity of PTT/ABS blend with 0.5 and 1 wt% of MWCNT was 6.3 × 103 Ω.cm and 4.2 × 103 Ω.cm, respectively, corresponding to a decrease of seven orders of magnitude in comparison with the PTT/ABS-40/60 blend (6.8 × 1010 Ω.cm). Probably, the electric percolation network occurs more easily in the PTT phase, than in ABS domains, so the high concentration of ABS acts as a barrier for electron flow, thus indicating a preference location of MWCNT on the PTT phase on PTT/ABS blends.

5.4 Effect of Antistatic Agent Functionalization on Electrical Properties of PTT Composites Considering a polymeric composite, the chemical compatibility between the matrix and the antistatic agent is essential to determine the EPT of the material, once the strong interaction between the components improves the filler dispersion, favoring the formation of a conductive pathway [15]. So, chemical functionalization of MWCNT can promote strong interfacial bonds with polymers by the addition of functional groups, as carboxyl groups, on the filler surface to interact and to improve dispersion within the matrix, thus making nanocomposites possess improved properties [65]. This interaction between a functionalized CNT and a polymer can be due to hydrogen bonding by the carboxylic groups from f-MWCNT and the PTT chains [66], as shown in the scheme of Fig. 11. The effect of MWCNT functionalization on the electrical properties of PTT was investigated. Figure 12 shows the influence of the addition of 0.5 and 1 wt% of f-MWCNT on the electrical resistivity of PTT and PTT/ABS blends. It is possible to observe that the addition of f-MWCNT decreased the electrical resistivity in all cases. However, this reduction is much more expressive in the PTT/fMWCNT composite, possibly indicating and confirming that the ABS phase on the PTT matrix impairs the transport of electrons.

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Fig. 11 Scheme showing the interaction between f-MWCNT and PTT chains [Source Author]

Fig. 12 Electrical resistivity of PTT and PTT/ABS blends with f-MWCNT: Effect of addition of functionalized f-MWCNT [Source Author]

As shown in Fig. 12, the electrical resistivity of PTT/ABS/MWCNT nanocomposites with 0.5 wt% of MWCNT is in order of 103 Ω.cm; when added the same content of f-MWCNT, the electrical resistivity of PTT/ABS/f-MWCNT nanocomposites is in order of 1010 Ω.cm. The EPT occurs at higher concentrations, greater than 0.5 wt%. So, in this case, the EPT is higher than in nanocomposites containing non-modified MWCNT. The electrical conductivity of carbon fillers may be related to the perfection degree in the arrangement of conjugated chemical bonds established by their carbon atoms. It is known that the chemical functionalization by the oxidation process disrupts the graphitic plane of CNT. Moreover, the process may lead to the creation of open-end tubes, holes on the surface, and shortening of the tubes, which decreases the AR. Besides the advantages of the oxidation process, some drawbacks

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are inevitable, such as the impairment of the electron transport mechanism, leading to an increase in the EPT [15].

6 Conclusions This chapter reviewed the concepts about the electrical properties of PTT-based polymer blends, composites, and nanocomposites for applications in antistatic packaging. The decrease in the electrical resistivity of PTT is essential to guarantee the ESD protection necessary for such application. In this point of view, it investigated the effect of some aspects, such as the aspect ratio of three different fillers (CNT, graphene nanoplatelets, and graphite), the use of a compatibilizer agent (PTT-g-MA), the addition of a second phase (ABS), and the modification of a filler (MWCNT functionalization) on the electrical resistivity of PTT-based polymer blends, composites, and nanocomposites prepared by melting processing method. The main results showed that it is possible to obtain composites to prepare antistatic packaging based on PTT as a polymer matrix, due to the reduction of the electrical resistivity in the PTT systems, revealed by the EPT in the presented graphs. However, the choice of the necessary parameters will depend on the filler characteristics and content, and not less importantly, the interaction between filler and matrix to guarantee the correct transport of electrons offered by the antistatic agent. Acknowledgements This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brazil (CAPES), Finance Code 001. The authors thank FAPESP (process 2020/12501-8) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico, process 310196/2018-3, 405675/2018-6, and 440312/2021-3) for the financial support.

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Chapter 14

Comparative Study of Physical, Chemical, and Dyeing Performances of PET, PTT, and PET/PTT Bicomponent Filaments Marwa Souissi, Ramzi Khiari, and Nizar Meksi

1 Introduction Polyester is currently the most important synthetic textile fiber in the world. It is in second place behind cotton in terms of production and consumption. According to a press report published in 2007 [21], the world production of polyester fibers was estimated at 25 million tons with a growth of 5% per year. This production represents approximately 75% of the production of all synthetic raw materials in the world. Polyethylene terephthalate (PET) is the most widely used type of polyester in textile applications followed by other types of polyesters such as polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), and polyethylene naphthalate (PEN) [70]. The literature reveals that there has been a great deal of interest in polyester fibers. Several studies have focused on improving their performance in terms of durability [74], mechanical resistance [48], water permeability [43], recovery elasticity [1, 58, 88], biodegradability [28], thermal comfort [82], etc. In this context, conventional polyester filaments can no longer meet the demands of the constantly evolving and changing textile market. To meet these demands, so-called bicomponent, threecomponent, and even more filaments combining several types of polyester have been developed. This study focuses on the various polyester filaments (PET), (PTT), M. Souissi · R. Khiari (B) · N. Meksi Laboratory of Environmental Chemistry and Clean Process (LCE2P-LR21ES04), Faculty of Sciences of Monastir, University of Monastir, 5019 Monastir, Tunisia e-mail: [email protected] M. Souissi · N. Meksi National Engineering School of Monastir, University of Monastir, 5019 Monastir, Tunisia R. Khiari Higher Institute of Technological Studies (ISET) of Ksar-Hellal, 5070 Ksar-Hellal, Tunisia University of Grenoble Alpes, CNRS, Grenoble INP, LGP2, 38000 Grenoble, France © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 A. R. Ajitha and S. Thomas (eds.), Poly Trimethylene Terephthalate, Materials Horizons: From Nature to Nanomaterials, https://doi.org/10.1007/978-981-19-7303-1_14

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(PBT), and (PEN) in particular polyethylene terephthalate (PET) and polytrimethylene terephthalate (PTT), and we will detail their compositions, their manufacturing processes, their properties, and their fields of application. Particular attention will be paid to the description of the bicomponent PET/PTT filaments. A final part of this study will subsequently be devoted to the description of the dyeing of these polyester filaments with disperse dyes.

2 Polyester Filaments Polyesters are synthesized by polycondensation reactions between diacids and diols [56]. The most marketed polyesters and the most used in the textile field are polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Table 1 summarizes the chemical formulas of diols and terephthalic acid for synthesizing these three polyesters PET, PTT, and PBT [70]. – Polyethylene terephthalate (PET): Polyethylene terephthalate (PET) is the most commonly used polyester fiber. It is marketed under various names: Mylar, Tergal, Dacron, and Terylene [70]. PET is made from terephthalic acid and ethylene glycol. Indeed, terephthalic acid is synthesized by air oxidation of p-xylene (1,4 dimethylbenzene) which is a petrochemical compound [18, 50, 74]. Table 1 Diols and diacids used in the synthesis of the three polyesters: PET, PTT, PBT, and PEN Acid

Diol

Terephthalic acid HO

Ethylene glycol OH

C

C O

Resulting polymer H

HO

Polyethylene terephthalate (PET)

H

C

C

H

H

OH

O

O

C

C

O

(CH2)2

O

O

n

1,3-Propane diol HO

H

H

H

C

C

C

H

H

Polytrimethylene terephthalate (PTT) OH

H

O

O

C

C

O

(CH2)3

O n

1,4-Butane diol H

HO

H

H

OH OH O

HO

O

O

C

C

C

C

C

C

H

H

H

H

Naphtalene-2,6-dicarboxylic acid Ethylene glycol O

Polybutylene terephthalate (PBT) H

H

H

C

C

H

H

OH

OH

O

(CH 2)4

O n

Polyethylene naphthalate (PEN) C

O C

O

(CH2)2 n

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– Polytrimethylene terephthalate (PTT): Polytrimethylene terephthalate (PTT) is made using 1,3-propane diol as the diol. This polyester is marketed by the firm Shell Chemical under the name Corterra [14, 32, 40]. It remained a little-used polymer for a long time, not because it lacked good physical and chemical properties and potential applications, but because of the high cost of synthesizing its original monomer (1,3-propane diol). The latter is made from acrolein, a product used among other things as an herbicide. It is toxic, difficult to transport, and not very efficient in converting to 1,3-propane diol. These technical problems therefore slowed down the launch of this fiber on the market [13, 14, 68]. But today there is a great deal of interest in PTT fiber, thanks to Shell’s recent development of a new process for the synthesis of 1,3-propane diol. The latter is characterized by a very low-cost price [86]. – Polybutylene terephthalate (PBT): Polybutylene terephthalate (PBT) is made from butylene glycol (1,4-butane diol) as a diol. PBT crystallizes much faster than PET. This fiber is the most recent of the polyester fibers already mentioned. Indeed, it was recently launched on the market by the company Nylstar under the name of “Elité” [81, 87]. PBT has a melting point which is lower than that of PET. Therefore, it is easier to melt spinning [21]. The resulting filaments are rather more elastic than PET. They are also known for their high degree of white which persists even after prolonged aging. PBT filament is increasingly produced and used in the textile sector, despite the price of butylene glycol being very high compared to that of ethylene glycol. This obviously leads to a price of PBT more expensive than that of PET. – Polyethylene naphthalate (PEN): The last family of polyesters is polyethylene naphthalate (PEN). It was discovered in 1948 [15]. PEN filaments were marketed in 2002 by the company Amoco under the trade name of Pentex [27]. They are made from ethylene glycol and naphthalene-2,6-dicarboxylic acid. This polyester has a higher melting point and tensile modulus than PET. Thus, PEN filaments are ideally suited for the manufacture of low elongation, high strength industrial yarns and tire cords [39]. In this research work, we will focus in what follows on the first two types of polyesters, namely polyethylene terephthalate (PET) and polytrimethylene terephthalate (PTT). They will be used in the production of bicomponent filaments.

2.1 Synthesis of PET and PTT Polyester Filaments 2.1.1

Synthesis of PET Filaments

The synthesis of PET filaments is carried out continuously through two stages: esterification and polycondensation [2]. The reaction scheme summarizing the synthesis of PET is illustrated in Fig. 1.

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First step : Esterification

Second step : Condensation Fig. 1 Reaction scheme for the synthesis of polyethylene terephthalate. Reprinted with permission from Awaja and Pavel [2]

In fact, in order to synthesize polyethylene terephthalate (PET) filaments, we first start with the esterification reaction. Then thanks to the action of dimethyl terephthalate and ethylene glycol, we obtain bis-di-hydroxyethyl-terephthalate and small amounts of oligomers. The temperature used varies from 150 to 210 °C. The second step is a polycondensation reaction carried out by heating under pressure and at an elevated temperature (270 °C). During this step, the molecules weld together with the elimination of ethylene glycol, which gives PET. It is a transparent product, melting at 250 °C which will be used in the manufacture of the polyester filament. A by-product which is ethyl glycol is also obtained [34]. In recent years, a new industrial manufacturing process has appeared. It actually consists of using direct esterification from acid terephthalic and ethylene glycol [34]. This new process for synthesizing PET filaments has improved the quality of the polymer formed. It also made it possible to reduce production costs and use a higher speed during the polycondensation reaction, which advantageously eliminated the use of catalysts.

2.1.2

Synthesis of PTT Filaments

The synthesis of PTT is carried out by direct esterification like PET. However, PTT is polymerized in a very different way from PET [13]. Metal salts based on titanium or tin are used as polymerization catalysts [27, 49]. These catalysts are added to the final vacuum polymerization step at 255–270 °C. PTT is a semi-crystalline polymer

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Fig. 2 Polytrimethylene terephthalate (PTT) synthesis reaction [13]

synthesized by a synthetic reaction between terephthalic acid and 1,3-propane diol according to the reaction scheme as shown in Fig. 2 [29, 64].

2.2 PET and PTT Filament Manufacturing Process The manufacturing process of PET and PTT filaments is done by the melt spinning operation [21]. As shown in Fig. 3, the first manufacturing step is to synthesize the polyester from the pure reagents. These starting reagents are introduced into a mixer called an inter-exchange reactor to form a paste which continuously feeds the esterification autoclave. In the case of the synthesis of PET, the reaction takes place under slight pressure and at temperatures between 245 and 280 °C [27]. The melting temperature of PTT is much lower than that of PET (228 °C). This is due to the glass transition temperature of the PTT which is equal to 40 °C. This glass transition temperature is much lower than that of PET [14]. The spinning process can be continuous or batch. In this case, the polymer has a very specific melting point. Once melted, the polymer is immediately sent to be spun [27]. The same is true for discontinuous spinning. Then, the synthesized polymer is put in the form of solid granules easy to store and transport. These granules are then

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Terephtalic acid

Glycol

Interchange reactor Continuous process Towards spinnerts

Autoclave

Discontinuous process Casting Crusher

Wheel Cooling Polymer grain Fig. 3 General steps in the synthesis of polyesters

remelted by the use of an extruder in order to transform them into an appropriate state of viscosity, physically and chemically stable [21]. It should be noted that the continuous spinning process, despite its more delicate implementation, still allows obtaining a filament with better quality. Figure 4 illustrates the process for spinning polyethylene terephthalate filaments. The polymer in the molten state passes through various filters in the spinning pack which aims to remove all impurities. The PET polycondensate is then melted at 290 °C under very high pressures and then extruded through dies (500–10,000 holes). The diameter of the holes is around 250 µm. The sections of the capillaries can be round (in the majority of cases) or arbitrary depending on the type of wire to be obtained [19]. On leaving the die, the filaments must be solidified as quickly as possible, without being deformed, and preventing them from sticking together. The cooling can be done by cold air or water in the chimney of the die. Air cooling is better because identical cooling is obtained inside and outside the filaments. Solidification takes place very quickly, which makes it possible to achieve very high spinning speeds (>1000 m/min) [34]. Drawing is an essential operation and conditions the quality of the filament obtained. This phase consists of aligning, lengthening, and unfolding the macromolecular chains that make up the filament. Increasing the draw rate increases the strength of the filament and decreases the elongation at break. In addition, this drawing operation can be carried out directly at the outlet of the dies, or subsequently depending on the type of yarn desired [34]. In the case where the drawing is separated from the spinning, an unstretched filament of the LOY type (low orientation filament) is obtained.

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Polymer in the molten state Solidified filament

Pump Filter and distrubtion area Spinnert

Packaging

Cooling Finishing Fig. 4 Spinning process for polyester filaments. Reprinted with permission from Souissi et al. [75]

Depending on the speed at which the filament will be received, we will obtain four different types of filaments: MOY filaments (medium oriented filaments), POY filaments (partially oriented filaments), HOY filaments (highly oriented filaments), and FOY filaments (filaments completely oriented). To obtain a regular filament, it is, therefore, necessary to have a good base polymer quality and to master the drawing conditions (temperature and drawing speed) [21, 34, 85]. The last step is the sizing. It consists in applying a regular deposit of oil emulsion on the filament to facilitate its sliding in the various channels. The filaments are finally wound at a constant speed [19].

2.3 Properties of PET and PTT Filaments 2.3.1

Morphological Properties

Polyester filaments in their conventional form, i.e., having a circular cross-section are found in a wide variety of textile articles. They provide a soft and silky appearance, which dries quickly and has excellent mechanical resistance and good lightfastness. These polyester filaments can be used alone or mixed with other textile fibers in items such as swimwear, underwear, and upholstery fabrics [19]. In recent years, considerable attention has been paid to improving the performance of polyester filaments and expanding their fields of application. Modifications were thus made

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at the level of the spinning step in the molten state which over time has become the main technology for the manufacture of polyester filaments [3, 66]. Generally, in order to obtain polyester filaments with specific characteristics, it is necessary to have a good quality of polymer, to control the drawing conditions, and to choose the adequate shape of the hole die, which allows to obtain filaments with special sections [38, 51]. Indeed, filaments with special sections acquire physical, thermal, and mechanical properties different from those of ordinary synthetic or natural fibers [4, 17, 78]. These filaments are stiffer and bulkier, with low water absorption, low heat retention, with a bouncy drape to the touch, and lighter and bulkier in the hand than conventional synthetic fibers [61]. Filaments with special section geometries such as tetrachannel or cross-shaped sections have many other advantages as they wick sweat more easily and allow air to circulate more quickly. This behavior is due to their surface area being larger than those of circular section filaments while ensuring a pleasant touch and a feeling of comfort for the wearer [30, 54, 61–63, 68, 83]. Among the recently marketed filaments, mention may be made of those from the company DuPont, which has synthesized two new monofilaments having tetrachannel and cross-shaped cross-sections. Currently, they are marketed under the names Coolmax and Coolever, respectively [30, 68]. They are used in the manufacture of several textile articles such as sports clothes, casual clothes, jeans pants, and baby diapers [30]. Souissi et al. [75] carried out a study on the morphology of these two innovative filaments marketed under the names Coolever and Coolmax and the classic PET filament. Indeed, SEM photos were taken of the jersey knits and longitudinal views for three types of filaments. The obtained SEM images are illustrated in Table 2. These pictures confirm the geometric shape of the monofilaments. Indeed, it is clear that the filaments (A) have a conventional circular section, the filaments (B) have a cross-shaped section, and the filaments (C) have a flat section which is made up of four adjacent channels hence the name of tetrachannel.

2.3.2

Crystallographic Properties

In the polyethylene terephthalate (PET) macromolecule, the aromatic nucleus is planar and has C–C bonds associated with it on each side, which forms a rigid structure [21]. The ester functions of the PET chain are polar, the oxygen of the carbonyl group being negative and the carbon positive. The positive and negative charges of the ester functions of the different chains are attracted to each other. The chains will thus be arranged in the form of crystals. The resistance of the PET filament is also due to the phenyl groups which stack up in a regular manner, which therefore increases the solidity of the crystals [18, 20]. As regards the PTT filaments, they have a particularly advantageous crystal structure. The PTT mesh also has a triclinic structure. The O–CH2–CH2–CH2–O group belonging to the macromolecular chain of the polymer has a trans-left-left-trans conformation so that the chains form tight zigzags [9, 33].

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Table 2 SEM images of the polyester filaments studied. Reprinted with permission from Souissi et al. [75] Filaments

Filament arrangement in jersey knits

Longitudinal view of filaments

(A)

(B)

(C)

The behavior of the chains forming the PTT filaments can be likened to a coil spring because during elongation, the spacing of the PTT crystal lattice reacts immediately to the applied stress and the deformation can be reversible below its critical stress [13], while PET has a fully extended chain. Consequently, unlike the PTT filament, it does not exhibit good elastic recovery from strain [47]. Thus, the structural organization and orientation of macromolecules in PET and PTT filaments have a great influence on their mechanical properties and especially on their dyeing properties. Likewise, the crystallinity rate of PET filaments is equal to 62–79% while the PTT has a crystallinity rate that does not exceed 35–42% [37, 67, 68]. Therefore, due to their particular configuration and crystallinity levels, PTT filaments have more amorphous areas than PET filaments. These amorphous areas constitute the only possible diffusion path for a dye in the polyester filaments.

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Chemical Properties

The properties of polyester filaments depend on their molecular structure, molecular weight, and the conditions under which these filaments were made and spun. PET and PTT filaments have good resistance to weak acids, even at boiling temperature, and to most strong acids at room temperature. However, hot concentrated sulfuric acid and concentrated nitric acid dissolve them. Under the action of a concentrated and very hot alkaline solution, these polyester filaments undergo surface hydrolysis [20, 69]. PET and PTT polyester filaments are very sensitive to strong bases. For example, highly concentrated ammonia penetrates the structure and causes degradation of ester bonds and loss of physical properties [9, 37]. PET and PTT have good resistance to oxidizing agents such as conventional bleaching agents for textiles [20]. The hydrogen peroxide and bleach cause little deterioration in the case of PET filaments unlike PTT filaments which remain intact [20]. Both filaments are insoluble in most organic solvents. Only high-boiling chlorinated and nitrated aromatic derivatives, phenols, and N-methylpyrrolidone have the power to dissolve PET filaments under the effect of heat [9]. As to dyeability, PTT filaments are easier to dye with disperse dyes than PET filaments and this is due to their less crystalline structure. The optimum temperature for dyeing PTT filaments with disperse dyes does not exceed 100 °C, unlike PET which can be dyed at very high temperatures above 130 °C. In addition, the shades obtained from fabrics made from 100% PTT are darker than those obtained when dyeing fabrics from 100% PET at 130 °C [37].

2.3.4

Thermal Properties

The thermal properties of PET and PTT filaments depend on their manufacturing methods. The two important temperatures which characterize semi-crystalline polymers are the glass transition temperature (T g ) and the melting temperature (T m ). These two temperatures (T g ) and (T f ) relate to the amorphous and crystalline phases, respectively. The values of the glass transition temperatures are around 70–80 °C and 45–65 °C. For the melting temperature, they are generally around 250–260 °C and 223–228 °C in the case of PET and PTT filaments, respectively [12]. These thermal properties depend on the spinning conditions of the filaments and their crystallization. A recent study developed by Souissi et al. [75, 76] investigated the properties of two polyester filaments made of 100% PET having a normal circular section and 100% PTT having a tetrachannel cross-section (Fig. 5). The obtained results are summarized in Table 3. As can be seen, the PET and PTT filaments present a crystallinity rate equal to 56.7 and 54.54, respectively. Knowing that other authors [68] have shown that a 100% PTT filament having an ordinary circular cross-section has a crystallinity rate that does not exceed 40%. From this, it can be concluded that the geometry of the cross-section of a filament and the spinning conditions greatly affect the thermal properties of resulting filaments.

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PET filament

2

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100

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250

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-1 -2 -3 -4 -5 -50

0

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100

150

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250

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350

400

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Fig. 5 Thermal analysis of PTT and PET filaments. Reprinted with permission from Souissi et al. [75]

2.3.5

Physical and Mechanical Properties

The density of amorphous PET and PTT is equal to 1.38 and 1.33 g/cm3 , respectively [20]. These two polyester filaments exhibit high dimensional stability. They resist heat very well and are hardly flammable [69]. In addition, they resist light degradation very well and have high abrasion resistance [9]. PTT filaments are known for their

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Table 3 Thermal analysis (DSC) of PET and PTT filaments. Reprinted with permission from Souissi et al. [75] Filaments

Tf (°C)

Tc (°C)

Tg (°C)

ΔHf (g/J)

Xm (%)

PET

249

199

62

69.23

56.69

PTT

231

179

52

79.87

54.54

With T f, T c et T g are the melting, crystallization, and glass transition temperatures, respectively; ΔH f is the enthalpy of fusion, and X m is the rate of mass crystallinity

excellent elasticity and elastic recovery. These are superior to those of PET filaments [37]. The mechanical properties of filaments with special cross-sections namely Coolmax and Coolever and classic 100% PET filaments have also been investigated by Souissi et al. [75]. Obtained results are shown in Table 4. It is obvious that the three classic and innovative studied filaments have very different percentages of elongation. Then, filaments (B) having a cross-sectional shape exhibit an elongation percentage equal to 12.68%, compared to 8.09% and 8.08% for the other polyester filaments: (C) having a shape of the tetrachannel cross-section and (A) having a shape of the conventional circular section, respectively. These results can only confirm the morphology of the cross-section has an effect on the mechanical properties of the polyester filaments; this is evidenced by comparing the mechanical performance of the 100% PET filaments (A) and (B) having two different cross-sections. By evaluating the elastic recovery of the three filaments, it was found that the filaments (B) exhibit excellent elastic recovery. Indeed, although having undergone 50% of their breaking strength, they are able to recover 52.53% of their initial state after a single cycle. After 10 consecutive cycles, they persisted with a value greater than 37.84%. Likewise, they exhibit a permanent deformation that does not exceed 2.72% for an initial length equal to 500 mm. Thus, the mechanical performances of the filaments studied have shown that the geometric shape of the filaments has a great effect on their elastic recovery. It is also noted that the innovative filaments (B) with their specific cross-section have higher elasticity and elastic recovery values compared to conventional PET filaments (A) of the same composition. However, the 100% PTT filaments (C), having the shape of a tetrachannel section, do not have a good elastic recovery unlike the 100% PTT filaments having a standard Table 4 Mechanical properties of polyester filaments. Reprinted with permission from Souissi et al. [75] Filaments

Tenacity (CN/tex)

Elongation at break (%)

Elastic recovery after 1 cycle (%)

Elastic recovery after 10 cycles (%)

Permanent deformation (%)

(A) PET

27.43 ± 0.37

8.08 ± 0.15

43.10 ± 0.18

23.08 ± 0.11

3.45 ± 0.11

(B) Coolever (PET)

31.56 ± 0.07

12.68 ± 0.24

52.53 ± 0.12

37.84 ± 0.23

2.72 ± 0.23

(C) Coolmax (PTT)

26.52 ± 0.07

8.09 ± 0.35

49.63 ± 0.21

27.65 ± 0.31

2.97 ± 0.31

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circular shape which are known by their high elasticity and their high elastic recovery thanks to the flexibility of their zigzag-shaped molecular chain [13].

3 Bicomponent Polyester Filaments Recently, several works have succeeded in combining different polymers into a single filament in order to obtain so-called bicomponent, three-component, and even more filaments. These filaments are composed of two or more polymers extruded from the same spinnerets [26, 44, 71, 75, 76]. Bicomponent filaments are polymixed filaments made by special spinning techniques. According to the American Society of Testing Materials (ASTM), a bicomponent filament is defined as “a filament made up of two physically and/or chemically distinct polymer components in continuous and longitudinal contact within the filament.” According to US regulations (1997), the official term for a filament made from two or more components is bicomponent, although the most common terms such as bicomponent, cofilated, or cofil are used both in Europe and in the United States, while the term conjugated filaments are used in Asia [59]. The first commercial application of bicomponent filaments was introduced by the company DuPont in the mid-1960s [27]. It was a side-by-side hosiery filament called “Cantrese” composed essentially of two nylon polymers which, on retracting, form a tightly coiled elastic filament. At this time, other side-by-side bicomponent acrylic filaments were also manufactured for the production of certain knitwear. Therefore, the main goal of this blend of polymers with such specific spinning was to obtain improved properties for very particular end uses [6]. In the 1970s, other bicomponent filaments began to be produced in Asia, notably in Japan. Very complex and seemingly expensive spinning packs were used in the manufacturing process. These attempts have proven to be technically unsatisfactory and excessively expensive. Later, in 1989, a new spinning technique was developed using thin flat plates with holes and grooves to convey the polymers. This process was very flexible and very profitable [24]. Different types of polymers, such as polyester, polyamides, polystyrene, polyurethane, polyolefins, polylactic acid, soluble co-polyamides, and co-polyesters, have been used to spin bicomponent filaments. They can be made from two variations of the same generic polymer (polyethylene terephthalate (PET), polyacrylonitrile (PAN), polyamide (PA), polyethylene (PE), and polypropylene (PP)). They can also be made of two different polymer compositions such as (PET/PBT), (PET/PA), and (PA/Spandex) [59]. The two polymers used in these cases differ in physical and chemical properties such as molecular weight, mechanical strength, melting temperature, and crystallinity [46]. Through the use of bicomponent filaments, the functional properties of both components can be exploited in a single filament. The characteristics of bicomponent filaments depend on the nature and properties of the materials used, their

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arrangement in the filament, their relative proportions, and the thickness of the filament obtained [53]. However, the spinning of bicomponent filaments represents the greatest challenge for the textile fiber industry. Recently, new bicomponent filaments from DuPont are newly marketed under the names T400 polyester and T800 nylon. These filaments have become very popular in the market.

3.1 Bicomponent Filament Spinning Processes Today, bicomponent filaments are melt spun in a specially designed spinneret. As shown in Fig. 6, two extruders and two separate metering pumps are used for the two components. The ratio of polymers can be controlled by varying the speed of the metering pumps [89]. The choice of polymers is a crucial factor in the spinning of the bicomponent filament. The morphology of the latter strongly depends on the relative amounts of each polymer and on the relative viscosity of the two polymers. In the case of two polymers having two different viscosities, the polymer of lower viscosity will tend to encapsulate the one with higher viscosity. This parameter is extremely important for spinning filaments of shell/core configurations where the shell must have

Fig. 6 A spinning process for bicomponent polyester filaments. Reprinted with permission from Souissi et al. [75]

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a lower viscosity while the core has a higher viscosity [59]. In addition, studies of the bicomponent filament spinning process have proven that the draw ratio, heat set temperature, and draw temperature are the main key variables to result in an efficient spinning process. During stretching, the difference in shrinkage between two polymers was found to be the main cause of crimp contraction [62]. An analysis of the effect of spinning and drawing conditions on the crimp contraction for a side-byside bicomponent filament composed of two different PTTs showed that the draw ratio was the most critical variable to control it. Increasing the stretch rate caused a difference in shrinkage between the two parts of PTT and caused poor adhesion and the possibility of splitting of the components that make up the filaments [63]. For a successful spinning of bicomponent filaments, it is, therefore, necessary to ensure above all the compatibility of the two components from the point of view of viscosity which should be sufficiently high, and the extensibility of the two polymers which should also be comparable, otherwise, a fractionation can occur produced [71].

3.2 Classifications of Bicomponent Filaments Since their inception, bicomponent filaments have undergone significant development and presently come in different configurations and different cross-sections each having very specific end uses. In the case of PET, for example, it can be combined with PTT, PBT, and PP. Bicomponent filaments can be classified according to their configurations into bark/core, side by side, islands/sea, and slices of cake. These basic configurations can be adapted depending on the properties of the desired filaments or yarns. – Side-by-side configuration: In this configuration, the two polymers occupy part of the fibrous surface. Each polymer is divided along the length into two or more distinct regions of the cross-section. Depending on the selection of polymers, this filament may develop a latent crimp that is greater than the shell/eccentric core configuration. – Shell/core configuration: In this configuration, one of the components called the core is completely surrounded by the second component called Shell. In this case, the concentricity or the eccentricity of the core can be adjusted according to the final application. If product strength is the primary concern, two-component concentric filaments are used. Otherwise, where bulkiness is necessary to the detriment of strength, the eccentric configuration of the bark with respect to the core of the bicomponent filament will be used. Bicomponent filaments having a shell/core configuration are able to retain the individual properties of each component. Bicomponent filaments with a polypropylene shell around a nylon core, for example, potentially exhibit the wear resistance of nylon and both the stain resistance of polypropylene. A strong bond must be established between the two materials to avoid cracking of the filaments [59, 60].

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– Cake slice configuration: This construction consists of several parts similar to “slices of cake” which touch at the level of the tips. Each piece of cake of polymer A is flanked on both sides by polymer B. These filaments are designed so that the different pieces of cake decompose in the event of mechanical actions and produce microfibers of 0.1 at 0.2 denier. – Island/Sea configuration: In this configuration, polymer A forms the islands while polymer B forms the sea. This form makes it possible to integrate a large number of fine threads of a fibrillar polymer in a matrix of a soluble polymer. Dissolving the latter makes it possible to produce a fabric based on ultra-fine microfibers. This process makes it possible to obtain finer filaments than the direct extrusion of fine filaments. Regardless of the choice of constituents, the two components may or may not be compatible. The first category results in a single homogeneous phase, and the spinning resembles the spinning of single-component homopolymers. The incompatibility between the polymers results in a separation phase. As a result, the spinning of these bicomponent filaments is complex and requires a lot of control before and after each step in order to ensure the compatibility of the two polymers [11, 59].

3.3 Areas of Application of Bicomponent Filaments The advantage of bicomponent filaments lies in their improved functionality. The fundamental shell/core cross-section, for example, is useful in many applications requiring engineering polymers. It makes it possible to obtain low-cost polyester filaments with better properties. The side-by-side bicomponent filaments exhibit good elasticity and rely on the difference in shrinkage between the two polymers. These filaments are increasingly manufactured to meet the many applications requiring good dyeing capacity [79, 80], decreased flammability, increased light, and heat stability [44, 69], and improved elasticity [71] and elastic recovery [26]. Nowadays, bicomponent filaments are increasingly used for applications in the field of hygiene, the manufacture of conductive fibers, elastic fibers, composites, and nonwovens as well as sporting goods [84].

4 Bicomponent Filaments (60% PET, 40% PTT) Side by Side In 2002, the DuPont company developed a new bicomponent (PET, PTT) filament under the name Elastomultiester [67]. The name emphasizes that this filament is elastic, multi-component, and polyester-based. This innovative filament is defined as “a fiber formed by chemical interactions of two or more distinct macromolecules

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Fig. 7 Cross-section of bicomponent filaments (T400) [77]

(none of which exceeds 85% by mass) containing ester groups as the dominant functional unit (at least 66%) and that after some stretch quickly returns to its original length when the tension is removed” [67]. In 2003, this filament was marketed under the name T400 by the company DuPont. Its chemical composition is 60% polyethylene terephthalate (PET) and 40% polytrimethylene terephthalate (PTT), which are arranged side by side (Fig. 7). The major interest advanced by the company DuPont for this new two-component filament is to eliminate the use of elastane filaments which pose a lot of problems during specific treatments for stretch-type denim items. Indeed, the latter has poor resistance to chlorine. In addition, they easily lose their elasticity, elastic recovery, and dimensional stability following high-temperature treatment.

4.1 Spinning Processes The bicomponent filament (40% PTT, 60% PET) is made from two distinct polymers, which have different shrinkage properties. This causes the filament to form a permanent spiral. After being exposed to heat during the standard finishing process, the coil tightens even more. Unlike textured fibers and filaments which develop their elasticity through mechanical processes, the physical spiral structure of this bicomponent filament provides permanent elastic recovery [37]. In order to keep this main characteristic of the bicomponent filament, certain conjugate spinning conditions must be respected [37]. Studies have shown that maintaining the same or very similar viscosities of two polymers during the melting step is one important condition among others for obtaining spirals [61–63]. With regard to the heat treatment which

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follows the melt spinning, it appears that a temperature of 20–30 °C higher than the Tg of PET is the optimum condition to also obtain a spiral appearance [71].

4.2 Properties of Bicomponent Filaments (60% PET, 40% PTT) 4.2.1

Morphological Properties

Souissi et al. [75] studied the morphology of bicomponent filaments (PET, PTT). For this, the scanning electron microscope (SEM) was used to study the surface structure and morphology of bicomponent filaments (60% PET, 40% PTT). The images of the transverse and longitudinal sections obtained are presented in Fig. 8. By observing the photos (Fig. 8a, b), it can be seen that the bicomponent filaments (60% PET, 40% PTT) have latent crimps which explain the elasticity of the resulting yarn and its power to high elastic recovery. It is also observed that each filament is composed of two adjacent strands of PET and PTT arranged side by side. These observations confirm the results reported by several authors in the literature [44, 46, 53]. The image of the cross-section of the filament (Fig. 9 shows two circular surfaces side by side but having surfaces of different sizes; the largest corresponds to the PET strand (almost 60% of the total surface and the smallest corresponds to the PTT strand (almost 40% of the total surface [67]. The diameter d1 of the first strand of PET is equal to 11.63 µm while the diameter d2 of the second strand of PTT is equal to 7.94 µm. This clearly confirms that the mass of PET is greater than the mass of PTT in these bicomponent filaments.

4.2.2

Thermal Properties

Souissi et al. [75, 76] studied the thermal behavior of bicomponent filaments (60% PET, 40% PTT). These filaments were explored through analysis (DSC) (Fig. 10). Two heating–cooling scans were performed. For each type of filament, the glass transition temperature (T g ) and the melting temperature (T f ) were collected from the first heating cycle while the crystallization temperature (T c ) was deduced from the first cooling cycle. DSC analysis of the bicomponent filaments (60% PET, 40% PTT) shows the existence of two main peaks. The first peak is located at a temperature equal to 248 °C. It corresponds to the melting point of polyethylene terephthalate (PET). The second significant peak is observed at 222 °C and corresponds to the melting point of (PTT) as reported by Hoock [36], Piccinini et al. [30, 67, 68]. In addition, the DSC thermal analysis makes it possible to deduce the value of the glass transition temperature (T g ) as well as the mass crystallinity rate. These two parameters are crucial for each material to be dyed [6].

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(a)

(b)

(c)

(d)

(e)

(f)

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Fig. 8 SEM pictures of bicomponent filaments (60% PET, 40% PTT). a, b Configuration of the filaments in the yarn; c, d longitudinal view; e, f sectional view [77]

Several researchers have proven that the lower the glass transition temperature, the more easily the dye fits into the amorphous areas of the filament. In fact, below the glass transition temperature, the molecules of the polymer have practically no movement. So, the diffusion of the dye is almost impossible. However, when the glass transition temperature is reached, the fiber has sufficient energy to allow the segments of the polymer chains to rotate. Once these segments move, space will be freed up to allow the other segments to move in their turns. The onset of segment movement takes place over a narrow temperature interval that includes the glass transition temperature [6, 72].

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Fig. 9 SEM picture of cross-section of (60% PET, 40% PTT) bicomponent filament [77]

2

Bicomponent filament (60% PET, 40% PTT)

1

-1

Exo

Heat Flow (mW)

0

-2

-3

-4

-5 -50

0

50

100

150

200

250

300

350

400

Temperature (°C)

Fig. 10 DSC analysis of bicomponent filaments (60% PET, 40% PTT). Reprinted with permission from Souissi et al. [75]

The results obtained by Souissi et al. [75, 76] show that bicomponent filaments (60% PET, 40% PTT) have the lowest value of (T g ) (equal to 49 °C), which proves that their tinctorial affinity to disperse dyes is quite low important [6, 72]. Likewise, by applying Fox’s law [31], the estimated glass transition temperature was determined for each of the two polymers which constitute the bicomponent filaments (60% PET, 40% PTT). The estimated temperatures are, respectively, equal to 37 and 62 °C for PTT and PET. As reported by Souissi et al. [75, 76], the PET and PTT components

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exhibit two mass crystallinity levels equal to 45% and 38%, respectively. This again asserts that the bicomponent filaments will likely exhibit the best dyeing yields over conventional 100% PET polyester filaments.

4.2.3

Crystallographic Properties

Crystallographic characterization of the various polyester filaments from the crystallographic point of view was carried out by Souissi et al. [75] by performing an analysis by X-ray diffractometry (XRD). The polyester filaments studied are (A) 100% PET filament of circular cross-section, (B) 100% PET filament with a transversal section in the form of a cross, (C) 100% PTT filament of cross-section of tetrachannel shape, and (D) bicomponent filaments (60% PET, 40% PTT). The results of this analysis for the studied filaments are also summarized in Table 5. It can be observed that the 100% PET filaments (A) and (B) have the same characteristic angles of diffraction peaks (2θ). The values obtained for (2θ) are close to those found in the literature [16] which are equal to 17.0°, 23.4°, and 25.8° and which coincide with the Miller indices. (h, k, l) of the characteristic planes (010), (110), and (100), respectively. Therefore, the basic crystal structure of the studied filaments is triclinic (a, b and c), unit cell sizes were thus determined for each filament, and the results are summarized in Table 5. As regards the filaments (C), which are composed of 100% PTT, it can be seen that the characteristic peaks correspond to those of the filaments (A) and (B) (with 100% PET) because indeed the two polymers (PTT and PET) do not have the same number of methylene groups, and in the case of PTT, it has a softer trimethylene sequence which has a trans-left-left-trans conformation. Thus, the molecule in space is triclinic whose diffraction angles are approximately 17.0°, 22.5°, and 25.5° which correspond, respectively, to the planes of Miller indices (100), (010), and (110) [72]. Likewise, in the case of the bicomponent filaments (60% PET, 40% PTT) which are the subject of this thesis, it is observed that they exhibit the same peaks characteristic of PET and PTT. In addition, by observing the results of Table 5, it can be seen that the degree of crystallinity is equal to 58% in the case of the PTT filaments (C) having Table 5 Results of DRX analysis of studied filaments. Reprinted with permission from Souissi et al. [75] Filaments

2θ1 (°)

2θ2 (°)

2θ3 (°)

Xv (%)

a (Å)

b (Å)

c (Å)

(A)

16.9

23.4

25.7

60.0

4.85

6.03

12.81

(B)

17.6

22.7

25.5

58.2

4.84

5.90

13.13

(C)

17.4

22.5

25.7

57.9

4.80

5.90

13.13

(D)

18.8

23.4

25.5

56.6

4.84

6.08

13.40

With θ1 , θ2 , and θ3 are the angles of the diffraction peaks, Xv is the degree of crystallinity; a, b and c are the parameters of the crystal mesh of the studied polymer

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a tetrachannel section which is flatter and compact than the filaments made of 100% PTT classics of circular section [68]. X-ray diffractometry (XRD) analysis determined the degree of total crystallinity of the bicomponent filament (D). The degree of crystallinity obtained is equal to 57% which is less important than the degree of crystallinity of monofilaments composed of 100% PET and 100% PTT. Thus, the filaments (D) have more amorphous areas which makes them more accessible to dyeing. This also gives them a great elasticity which is attributed to the arrangement and orientation of the polymers in the chain. Thus, unlike the FTIR and DSC analyses, the XRD analysis showed that despite the same composition of the filaments (A) and (B), their rate of crystallinity is not similar. This fact can probably have an effect on their dyeing ability. In addition, in the case of the filaments (C) having a tetrachannel cross-section, their compact and flat configuration influenced the distribution of molecular chains in space, and therefore, the crystallinity became high.

4.2.4

Mechanical Properties

Bicomponent filaments (60% PET, 40% PTT) are known for their excellent elasticity and elastic recovery. Therefore, Souissi et al. [75, 76] find that a mechanical characterization seems important to evaluate these remarkable mechanical properties. A tensile test on these filaments was carried out accordingly by these authors to the ISO 3377-2 standard. Likewise, in order to compare the elasticity of bicomponent filaments (60% PET, 40% PTT) with other polyester filaments, tensile tests were carried out. The results obtained show that despite their close toughness values, they exhibit very different percentages of elongation. Indeed, the bicomponent filaments (60% PET, 40% PTT) (D) have a greater maximum elongation equal to 44.52% compared to 12.68%, 8.09%, and 8.08% for the other polyesters filaments: (B) having a crosssectional shape, (C) having a tetrachannel cross-sectional shape, and (A) having a conventional circular cross-sectional shape, respectively. These results can only confirm the excellent elasticity of the bicomponent filaments (60% PET, 40% PTT) subject of this thesis. By evaluating the elastic recovery of the four filaments [76] found that the bicomponent filaments (60% PET, 40% PTT) (D) exhibit excellent elastic recovery. Indeed, although having undergone 50% of their breaking strength, they are able to recover 69.23% of their initial state after a single cycle. After 10 consecutive cycles, they persist with a value greater than 58%. Likewise, they exhibit a permanent deformation that does not exceed 2.16% for an initial length equal to 500 mm. Thanks to their excellent elastic recovery, bicomponent filaments (D) can be used in the manufacture of technical textile articles. However, the other filaments (A), (B), and (C) do not withstand 50% of their breaking strengths as well: After 10 consecutive cycles, they tend to recover only 23.1%, 37.8%, and 27.6%, respectively. Thanks to these interesting properties of elasticity and elastic recovery, bicomponent filaments (60% PET, 40% PTT) are widely used in the manufacture of denim articles, work clothes, and fabrics for shirts, sportswear, and socks [19].

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5 Dyeing Polyesters Filaments Polyester fiber (PET) is a difficult fiber to dye. Its high crystallinity rate does not allow it to absorb water or swell, which considerably limits the penetration, migration, and affinity of dye molecules. Today, PET is dyed with disperse dyes which present a very wide range of colors with vivid nuances, good leveling power, and good lightfastness [6].

5.1 Disperse Dyes Disperse dyes are nonionic dyes, relatively insoluble in water at room temperature, and have limited solubility at higher temperatures. However, they do have some substantivity for hydrophobic fibers such as nylon, acetate, and PET, in which they are quite soluble. As their name suggests, these dyes are present in the dye bath as a fine aqueous suspension in the presence of a dispersing agent. The water dissolves a small amount of the disperse dye. The hydrophobic fibers then absorb the dye from the solution [21]. In 1923, British Celanese and British Dyestuffs Corp were the first companies to market this type of dyestuff. Such dyes, due to their lack of solubilizing groups, are practically insoluble in water. This means that they must be applied as an aqueous dispersion containing essentially particles of dye. Such a method of application naturally led to the adoption of the name “disperse dye” [21]. From 1950, the production of disperse dyes increased sharply, in parallel with the growth in world production of synthetic fibers, in particular PET fibers, and the production of which has been steadily increasing [7]. Disperse dyes differ in the rate at which their molecules migrate, their sensitivity to temperature changes, and their exhaustion rate in the dye bath. Table 6 shows a dye classification of disperse dyes into three types: low-, medium-, and high-energy dyes [7]. The molecular weight and the number of polar groups in the disperse dye molecule directly affect its dyeing properties. Low energy disperse dyes have small molecules and low polarity. They, therefore, have good migration power inside the fiber and therefore a high exhaustion rate [6]. The more the molecular weight and the polarity of the disperse dyes increase, the more the depletion rate of the dye bath decreases due to the poor migrating power of the dye molecules. On the other hand, the resistance to heat as well as the fastness to washing become better. In order to further improve Table 6 Dye classification of disperse dyes

Classification

Molecular weight

Polarity

Exhaustion

Low energy

Low

Low

High

Medium energy

Medium

Medium

Medium

High energy

High

High

Low

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With : • X and Y are alkyl or alcohol X Z

N=N

groups.

N Y

• Z is an alkyl, amine or nitro group. Fig. 11 Chemical structure of azo disperse dyes

the dyeing performance of high-energy dyes, it will be necessary to dye at high temperatures instead. Dyeing is then carried out either in an autoclave or by padding followed by heat treatment [6]. Disperse dyes can also be classified according to their chemical composition as follows [6, 7]. – Azo dyes: They represent around 60% of disperse dyes. Azo dyes are the most widely marketed of the disperse dyes. This is thanks to the simplicity of their production process. With this class of dyes, manufacturers can meet customer demands much more easily. This type of colorant achieves almost the full range of shades. The chemical structure of azo dyes is shown in Fig. 11 [7]. – Anthraquinone derivatives: About 25% of disperse dyes are anthraquinone dyes. They are used to having shades of red, purple, blue, and turquoise. In comparison with azo dyes of similar shades, anthraquinone derivatives are often characterized by greater clarity and better stability against hydrolysis and reduction. However, anthraquinone dyes exhibit low coloring strength and low molar extinction coefficient. This limits their use [7]. Their chemical structure is shown in Fig. 12. – Quinophthalone, methine, naphthalimide, naphthoquinone, and nitro dyes: They present the remaining 15% of disperse dyes. They are mainly used to produce yellow undertones. O

=

X’

With : X 'and Y' are amines, amides,

= O

Y’

aminoalcohols

Fig. 12 Chemical structure of anthraquinone disperse dyes

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5.2 Properties Disperse dyes have low solubility in water. In the dyeing step, a small amount of dye molecules is able to penetrate hydrophobic fibers such as cellulose acetate, nylon, or PET. The dye is much more soluble in fiber than in water. So deep tinctures are possible. The disperse dye particles are very small. Their large specific surface area ensures rapid dissolution to maintain saturation of the aqueous solution while the soluble dye transfers into the fiber [5, 6]. Disperse dyes are marketed in different forms: powders, grains, pastes, or aqueous dispersions. They all contain microfine particles of dyes. The majority of these particles have a diameter of less than 1 µm. Variable amounts of dispersing agents are also found therein. The granular forms of disperse dyes pour easily, dust free, and easy to weigh. The solid forms of disperse dyes, on the other hand, contain much more dispersant than pastes and liquid forms. This helps prevent the aggregation of particles during drying. Disperse dyes in powder or granules rarely contain more than 50% dye. The remainder is dispersant, small amounts of diluents, and oils. Disperse dyes in solution are useful for continuous dyeing. The sedimentation and aggregation of dye particles in pastes and liquids can result in colored spots on the dyed fabric [19]. Many disperse dyes degrade during dyeing if the bath pH is not well controlled. Some dyes are hydrolyzed by the action of acids or alkalis. The hydrolyzed form of the dye is of a different shade and in some cases different affinity for PET compared to the unhydrolyzed dye. An alkaline medium can cause permanent deterioration of the dye and thus decreases the dye yield. Thus, the use of a buffer system to alleviate all of these problems is necessary in this case [6, 10]. The wash and light fastnesses of dyes with disperse dyes on synthetic fibers are generally moderate and good. The lightfastness of disperse dyes can be very good in standard shades, but less so for pale shades [6].

5.3 Dispersing Agents The dispersing agents are mainly surface-active compounds. They reduce the surface tension of the water and accumulate on the surface of the fiber. They are used in virtually all wet-finishing treatments and in dyeing PET fibers with disperse dyes [7, 73]. Disperse dyes are poorly soluble in water. In addition, these synthesized dyes are often crystalline and of variable particle size. Therefore, the dispersions of the particles of these dyes in water will be uneven and weak [73]. In fact, disperse dyes are generally ground in the presence of a commonly anionic dispersing agent such as lignin sulfonates or sulfonic acid polycondensates. They thus facilitate grinding by preventing agglomeration of the dye particles and allow the dye to be prepared in powder or liquid form [73]. Although the dispersing agent aids in the dispersion of the dye in water, it also helps to grind coarse dye particles and maintain a stable dispersion during dyeing [22]. An additional dispersing agent is often added to the dye bath to maintain the

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Fig. 13 Solubilization of disperse dye in the micelle

stability of the dispersion and when the dyeing is carried out at high temperature [22]. In order to prevent the formation of an aggregate or agglomerate of the dye particles in the dye bath, the addition of a dispersing agent is essential. Dispersants are electrically asymmetric surfactants. They contain a polar end negatively charged in water and another nonpolar part directed toward the surface. The polar part is of hydrophilic character associated with the long aliphatic hydrocarbon chain of hydrophobic character. From a certain concentration of dispersing agent, sphericalshaped micelles begin to form and the disperse dyes trapped in the micelles tend to dissolve thus allowing the dye to have a much greater apparent solubility (Fig. 13) [22, 45].

5.4 Carriers The term carrier describes a type of accelerator particularly used in the dyeing or printing of hydrophobic fibers with disperse dyes. In fact, the dyeing of PET fibers with disperse dyes takes place with a very slow absorption rate even at boiling point. This is due to the low diffusion rate of the dye particles in the fiber. Aromatic compounds of small molecular size are then added to the disperse dye bath, in the form of a solution or emulsion. These make it possible to increase the speed of dyeing and improve the dye yield [6, 79]. Carriers can be classified into four groups: phenolic compounds, primary amines, hydrocarbons, and esters. The carriers which give the best results are generally based on halogenated aromatic hydrocarbons and orthophenylphenol which are sparingly soluble in water. The latter is present in the dye bath in the form of an emulsion [6, 79]. The most widely used carriers in the dyeing of PET fibers are butyl benzoate, methylnaphthalene, dichlorobenzene, diphenyl, o-phenylphenol, etc., while tripropyl phosphate, butyl benzoate, and phthalate are commonly used for dyeing cellulose acetate [7, 8]. During dyeing with

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disperse dyes, the carriers are largely absorbed by the PET fibers. They disrupt the internal structure of the PET fiber, allowing the dye to penetrate the interior of the fiber more quickly [7].

5.4.1

Carrier-Dye Interactions

Many theories have been proposed to explain the mechanism of action of carriers: Carrion-Fité [8] proved that PET-carrier interactions occur mainly by means of dispersal forces, hence the formation of a loose complex between the dye and the carrier, a complex that will enter the fiber more easily than the dye molecules alone. Iskender et al. [42] suggested that carriers were adsorbed by PET primarily due to nonpolar forces operating between the aromatic regions of both carrier and fiber, albeit with carriers bearing polar substituents, such as phenol, polar forces can also contribute to adsorption. Other researchers have found that the mode of action of the carrier results in an increase in the solubility of the dye in water. Therefore, an increase in the dyeing rate is then observed [23]. Another hypothesis which has been proposed as to the mode of action of the carrier is the possible formation of a liquid film around the surface of the fiber in which the dye is very soluble, thus increasing the rate of transfer in the fiber [52]. Other researchers have attempted to relate the rise of the carrier on the substrate to an increase in the water impregnation of the hydrophobic fibers, thus creating a medium accepting the partially soluble disperse dye [25, 55]. Other authors have shown that the mechanism of action of carriers results in a modification of the microstructure of the fiber. Thus, Ingamells et al. [41] observed a progressive reduction in the glass transition temperature (T g ) as the quantity of carrier increased. Indeed, a decrease in the glass transition temperature (T g ) of the polymer promotes movements of the polymer chain thus creating free volume and this accelerates the diffusion of the dye into the fibers.

5.4.2

Risks Associated with the Use of Carriers

A recent study developed by Pasquet et al. [65] evaluated the toxicity of carriers commonly used in dyeing polyester filaments with disperse dyes: benzoic acid, pdichlorobenzene, o-dichlorobenzene, diphenyl, and phenylphenol. Table 7 gathers the results found. From these data, it was found that phenylphenol is the most toxic and carcinogenic carrier followed by p-dichlorobenzene which is slightly toxic and possibly carcinogenic. All carriers have inherent drawbacks or dangers such as toxicity, bad odor, and vapor volatility. Therefore, the dyeing method with these carriers is far from being the best solution for dyeing PET fibers with disperse dyes [42, 65].

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Table 7 Assessment of the toxicity and carcinogenicity of some carriers. Reprinted with permission from Pasquet et al. [65] Carriers

Acute toxicity

Carcinogenicity

Ecotoxicity

Benzoic acid

Slightly toxic

–

Nontoxic

p-Dichlorobenzene

Slightly toxic

May be carcinogenic

Moderately toxic

o-Dichlorobenzene

Slightly toxic

–

Moderately toxic

Diphenyl

Slightly toxic

–

Moderately toxic

Phenylphenol

Hyper toxic

May be carcinogenic

Hyper toxic

5.5 Processes for Dyeing PET Using Disperse Dyes The dyeing of PET with disperse dyes can be carried out using three different processes: full bath dyeing with carrier, high-temperature dyeing without carrier, and heat-setting dyeing (thermosol process). The choice of one of these three processes is dictated by several factors such as the availability of the machines, the composition of the article to be dyed, and the set of characteristics requested by the customers [6].

5.5.1

Dyeing at 100 °C with Carrier

Figure 14 shows the thermal curve for dyeing PET with disperse dyes using a carrier. First, the bath is filled at 50 °C with the dye. After 10 min, the carrier is added. After stirring the carrier and dye assembly, the sample to be dyed is introduced into the dye bath. The temperature is then gradually raised to the boiling point and maintained for 50 min. Allow to cool to 80 °C and rinse. In general, the carriers used are nonbiodegradable. Three washing cycles are then carried out in order to remove the traces of the carrier that persist on the textiles. Nowadays, the use of conveyors in dyeing has greatly reduced since the development of machines suitable for dyeing polyester under pressure, at high temperatures in the vicinity of 130 °C. Nevertheless, the conveyors are still used in some dyehouses where pressure and high-temperature dyeing machines are not available. The amount of carrier required for dyeing decreases with increasing dye temperature. The use of a small amount of carrier is useful for dyeing at 110–120 °C as the low temperature dyeing releases less oligomers from the polymer and better preserves the bulk and elasticity of the fiber. The carriers are also useful for dyeing polyester/wool blends where there is a risk of damaging the wool at dyeing temperatures above 100 °C [6].

5.5.2

High-Temperature Dyeing Process

It is generally considered that high-temperature dyeing (of the order of 125–135 °C) in the absence of a carrier offers several advantages over 100 °C dyeing using the

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Temperature(°C)

100°C 80°C

50°C

A

B

Time(min) Adding carrier

Addingsamp le

Fig. 14 Thermal curve of dyeing polyester filaments using a carrier

Temperature(°C)

130°C

80°C 80°C 50°C

Time(min)

Fig. 15 The thermal curve of dyeing PET at 130 °C

carriers, i.e., shorter dyeing times, excellent penetration, and dye yield and, in some cases, better-resulting color fastnesses. This good dyeing performance of PET fibers can be seen as a consequence of the higher kinetic energy of the dye molecules and higher aqueous solubility of the dye at elevated temperatures. The thermal conduct of dyeing at high temperatures is illustrated in Fig. 15 [7, 57].

5.5.3

Dyeing Thermosol Process

The dyeing thermosol process PET fabrics was developed by the company DuPont. The first idea appeared in 1947 in the laboratory of DuPont. This process is mainly used today to dye the polyester part of blended fabrics (polyester/colon) [45].

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In this process, the material is padded in a bath containing the dye, thickener, dispersant, and acetic acid. Then, the scarf fabric is pre-dried, dried, and heat-sealed at about 1 min at a temperature ranging from 180 to 210 °C [19]. The dyeing mechanism relating to the thermosol process is based on the transfer of the sublimated dye to the PET fiber. In fact, during padding, the molecules of the dye are absorbed in the surface of the fiber. Then, during heat setting, this amount is migrated into the interior of the fiber. Finally, during cooling, the amorphous areas of the PET fiber contract. This ensures a strong fixation of the dye.

5.5.4

Description of the Dyeing Mechanism

The mechanism for dyeing PET fibers with disperse dyes can be summarized in three steps (Fig. 16). The first step involves the dissolving of the dye in the dye bath. Then, the second step is the adsorption of the dye dissolved in the dye bath to the surface of the PET fiber. Finally, it is the diffusion of the dye inside the PET fiber [5]. – The rate of dissolution of the disperse dye depends primarily on the size of its particles and its crystalline form. Indeed, the rate of dissolution of the dye is inversely proportional to the diameter of its particles. The smaller the particles of the dye, the easier the dissolution. The solubility and the rate of dissolution of the dye can be improved by the use of the dispersants. The latter are generally introduced into the dye powder during its manufacture [5]. The presence of the dispersant results in the formation of spherical micelles which allow the dye to change from the state of particles to the state dissolved in the aqueous phase. Therefore, the dye bath may contain an amount of the dissolved disperse dye, a dye trapped in the micelles, and a solid dye in particulate form so as to form the following equilibrium shown in Fig. 17. The disperse dye present in the micelles can be regarded as a reserve in dissolved dye. Thus, when some of the dye has been

Water

Fiber

. . .. .. . Particules du colorant en suspension

Mise en solution des particules du colorant

.. .. ....... ....... . Dye molecule on the surface of the fiber

Fig. 16 Dyeing mechanism of PET filaments with disperse dyes

Diffusion of the dye in the fiber

14 Comparative Study of Physical, Chemical, and Dyeing Performances … Fig. 17 The different forms of disperse dye in the dye bath

Particles

305

Dyes in micelles

Dissolveddyes

Dyes in the fiber

adsorbed by the fiber, the dye bath is “replenished” with the dye by dissolving the dye present in the micelles [22]. – The speed of adsorption of the dye by polyester fibers (PET, PTT, PBT) is influenced by several factors among which we can mention: the fineness of the fiber, the bath ratio, and the diffusion coefficient of the dye in the aqueous medium than in the fiber. – Polyester filaments have heterogeneous materials and the disperse dye must follow a tortuous path to avoid crystalline regions that it cannot enter. Finally, the drop-in temperature allows the fixation of the dye on the fiber. The dye is thus trapped between the macromolecular chains which take their initial configuration following this decrease in temperature. The diffusion of dyes in the fibers is linked to the molecular order, to the crystal mesh, and to the morphology of the polyester filaments. Therefore, in the case of dyeing of PET and PTT, for example, the diffusion coefficient is not the same. Hori et al. [35] have shown in their study on the dyeing of PET with Disperse Violet 1 that the most important parameters which influence the diffusion coefficient are the affinity of the dye, the swelling of the fiber, the enthalpy change required for free volume formation, and glass transition temperature. Different experiments have been carried out to establish a correlation between the diffusion coefficients and fiber structure, and two main models were developed to explain the mechanisms of migration inside polymers: the “pore” model and the “free volume” model. The pore model assumes that the dyes follow the path of the water in the pores. This model is not realistic and does not describe the diffusion mechanism of most hydrophobic polyester fibers since polyester absorbs only very small amounts of water (about 0.4%) and fact that they are generally dyed with dyes of which the solubility in water is restricted. However, the free volume theory makes it possible to characterize the diffusion of the dyes dispersed in the amorphous zones of the polyesters for temperatures above the glass transition temperature. The free volume theory states that the dye is attracted to the surface of the fiber and remains there until sufficient thermal energy is supplied to the system to allow the dye to diffuse into the fiber. Indeed, below the glass transition temperature, the molecules of the polymer have practically no

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movement so diffusion is almost impossible. Hori et al. [35] set up a new theory that consists in combining the two models of the pores and of the free volume.

5.6 Dyeing Bicomponent Filament (60% PET, 40% PTT) Zhuli et al. [89] studied the effect of dyeing and finishing bicomponent filaments (60% PET, 40% PTT) on their elasticity. Indeed, they carried out the dyeing of the bicomponent filaments at 130 °C for 20 min using the disperse dye CI Disperse EXSNF Black. The studied filaments were then subjected to an alkaline treatment. The results show that the bicomponent filaments lost 75% of their starting elasticity after the alkaline treatment. Likewise, a splitting between the two components PET and PTT of the filament was observed. Souissi et al. [76] studied the dyeing of bicomponent filaments (60% PET, 40% PTT) using three classes of disperse dyes, namely CI Disperse Red 60, CI Disperse Yellow 211, and CI Disperse Red 167.1 of low, medium, and high energy, respectively. The results of their studies show that the dye pH has no effect on the dye strength (K/S) in the case of dyeing bicomponent filaments (PET, PTT) with the three disperse dyes. It can be concluded that (K/S) value remains almost constant according to the dye bath pH. So, in order to have a cleaner process, pH value of 7 was chosen as the ideal value to dye bicomponent filaments. These authors also studied the effect of temperature on dyeing performances in order to deduce the optimum value to use for dyeing bicomponent filaments. Tested temperatures were 90, 100, 110, 120, and 130 °C. Obtained results for the high-energy dye, CI dye Disperse Red 167.1, show that increasing the dyeing temperature from 100 to 130 °C increases significantly the color strength (K/S). In the case of disperse dye having medium energy, the temperature required to have the highest color yield is 120 °C. Whereas, for the low energy dye, namely CI Disperse Red 60, the color yield (K/S) reaches its maximum value at a temperature of 110 °C. Indeed, the more the molecules of the dye have a lower molecular weight and a lower polarity, the better the migration inside the fiber and thus the higher the exhaustion rate at a given time and at a lower temperature. Souissi et al. [76] are also interested in evaluating the effect of dyeing duration in order to deduce the time needed to reach the dyeing balance and to have dye saturation at the amorphous areas in the fiber. For this, bicomponent filaments were dyed using the three studied disperse dyes by varying the dyeing time from 5 to 100 min (using a dyeing temperature of 130 °C and a neutral pH). Obtained results show that the value of the color yield (K/S) reached its maximum when the dyeing time is 40, 30, and 20 min for CI Disperse Red 167.1 (high energy), CI Disperse Yellow 211 (medium energy), and CI Disperse Red 60 (low energy), respectively. The short dyeing time observed in the case of the low energy dye can be explained by the fact that this dye has the lowest molecular weight and has a low polarity and therefore has a good migration power inside the fiber.

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In addition, these authors have proven that samples made of 100% bicomponent filaments (PET, PTT) dyed under optimum conditions presented a good level of evenness as well as a good union-shade of both components (PET and PTT) of filaments. They confirmed all the same that dyeing was well uniform throughout the textile substrates with a regular distribution of dyes on the whole samples. The evaluation of fastnesses of dyed samples with the three studied disperse dyes. According to ISO standards, 105-C06, 105-X12, and 105-B02 (used for wash, crock, and light fastnesses, respectively) were carried out by Souissi et al. [76]. Obtained results show that the samples dyed with CI Disperse Red 167.1 (high energy) present an excellent washing, rubbing, and light fastnesses due to its high molecular weight, followed by CI Disperse Yellow 211 (dye with medium molecular weight) and CI Disperse Red 60 (dye with low molecular weight). Other studies of Souissi et al. [76] were devoted to the comparison of the dyeing performance of bicomponent filaments against three different monofilaments with (A) PET circular section, (B) PET cross-sectional shape, and (C) PTT tetrachannel section. Obtained results showed that bicomponent filaments (D) present the best dyeing performances compared to the other monofilaments (highest value of (K/S)), more ecological dyeing process (saves of time, energy, and auxiliary products) besides their higher mechanical properties (elastic recovery and elasticity). This study, therefore, revealed very promising results and confirmed the great potential of bicomponent filaments which exhibit the best dyeing performance using a more ecological dyeing process (saving time, energy, and auxiliary products). Souissi et al. [77], in their most recent study, explored the possibility to dye bicomponent polyester filaments (PET/PTT) with an ecological and cleaner dyeing process. Chemical carriers which are toxic to humans and the environment will be substituted by ecological ones that respect nature, namely o-Vanillin, p-Vanillin, and Coumarin. Three different disperse dyes having different molecular weights were used. Different concentrations of the used carriers were tested and then evaluated. The comparison between ecological carriers and chemical ones was established and elaborated from the point of view of dye bath exhaustion, color yield, color coordinates, and colorfastness. From the results found in this study, it was demonstrated that p-Vanillin is the most suitable choice to be used as an ecological carrier replacing toxic carriers; it has allowed to obtain the best performance of dyeing with excellent fastnesses. It is also much less expensive and very abandoning, unlike o-Vanillin and Coumarin, as their synthesis is more complicated and they are much more expensive. Moreover, a comparative study between the performances of these new clean dyeing processes (using p-Vanillin) and that of the dyeing process at 130 °C (in the absence of carrier) has shown that this new ecological process presents results of similar or even better dyeing.

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6 Conclusion In this paper, a characterization of polyester filaments from the point of view of chemical composition, physical properties, mechanical properties, synthesis, and spinning process was carried out. Particular attention was paid to bicomponent polyester filaments (PET, PTT). Therefore, the main characteristic properties of these bicomponent filaments, their spinning process, and the different configurations of these bicomponent filaments have been explored. Techniques for dyeing PET fibers were presented. Disperse dyes, their classes, chemical compositions, solubility, and bath dispersion were discussed. Based on all the results obtained during the morphological, chemical, crystallographic, and mechanical characterizations developed using SEM, DSC, DRX techniques, and dynamometric tests, we can underline the great potential of bicomponent filaments (60% PET, 40% PTT) which exhibit excellent elasticity and elastic recovery compared to other innovative and conventional polyester filaments. In addition, it has been demonstrated that these bicomponent filaments exhibit a rate of crystallinity and a glass transition temperature lower than the other polyester filaments. This justifies their excellent dyeing yields at relatively low temperatures. These promising dyeing results can only encourage to manufacture more articles containing the bicomponent filaments (60% PET, 40% PTT) and to incorporate them in the fabrics of the denim, the work clothes, and the fabrics for the shirts, sportswear, and socks in order to give the wearer, the desired elasticity, and the desired comfort, but also to allow the manufacturer to use an economical and above all ecological dyeing process.

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