Cellulose Acetate: Properties, Uses and Preparation 9781536147049, 9781536147056

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CHEMISTRY RESEARCH AND APPLICATIONS

CELLULOSE ACETATE PROPERTIES, USES AND PREPARATION

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CHEMISTRY RESEARCH AND APPLICATIONS

CELLULOSE ACETATE PROPERTIES, USES AND PREPARATION

CALVIN ROBERSON EDITOR

Copyright © 2019 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. We have partnered with Copyright Clearance Center to make it easy for you to obtain permissions to reuse content from this publication. Simply navigate to this publication’s page on Nova’s website and locate the “Get Permission” button below the title description. This button is linked directly to the title’s permission page on copyright.com. Alternatively, you can visit copyright.com and search by title, ISBN, or ISSN. For further questions about using the service on copyright.com, please contact: Copyright Clearance Center Phone: +1-(978) 750-8400 Fax: +1-(978) 750-4470 E-mail: [email protected].

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Library of Congress Cataloging-in-Publication Data ISBN: H%RRN

Published by Nova Science Publishers, Inc. † New York

CONTENTS Preface Chapter 1

Chapter 2

Chapter 3

Chapter 4

Index

vii Thermodynamics of Acetates and Nitrates of Cellulose and Their Plastification V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova, N. Yu. Kokurina, V. N. Larina and K. V. Otvagina Cellulose Diacetate Matrices in the Luminescent Analysis of Ecotoxicants Svetlana M. Rogacheva, Anna B. Shipovskaya and Tamara I. Gubina Production of Cellulose Acetate from Agricultural Residues Rafael Garcia Candido Preparation of Sodium-Activated Natural Bentonite Clay Incorporated Cellulose Acetate Nanofibres by Free Surface Electrospinning and Its Proposed Applications Mohamed Basel Bazbouz

1

141

201

231 275

PREFACE Cellulose Acetate: Properties, Uses and Preparation presents data on thermodynamic characteristics (heat capacity, enthalpy, entropy, and Gibbs function) from 4 to 580 K cellulose acetates and cellulose nitrates, as well as the major plasticizers for these polymers, the temperatures of their relaxation and phase transitions, the effect of plasticizers on these characteristics of cellulose acetate and cellulose nitrate and the solubility of plasticizers in polymers. On the basis of the data obtained, diagrams of the physical states of the cellulose acetate and cellulose nitrate – plasticizer systems were constructed and analyzed in a wide range of temperatures and throughout the concentration range of the components. Cellulose diacetate has been used in the design of sorption matrices for the fluorescent analysis of polyaromatic and heterocyclic compounds. Thus, the physicochemical properties of cellulose diacetate solutions in a binary acetone-water solvent were analyzed along with the morphological, surface-energy, physicochemical and physicomechanical characteristics of film matrices in comparison with fiber ones. Additionally, the authors examine how the growth of CO2 emissions efforts led to the necessity for green material solutions that fit into a sustainable development policy and low environmental impact. The major barriers to produce cellulose-based products from agricultural residues are the heterogeneity of the raw material, the experimental conditions reproducibility, the heterogeneous

viii

Calvin Roberson

phase of the synthesis reaction, the difficulty of purification, the effluent disposal, and the control of the product quality. In the closing study, the authors provide a comprehensive review of electrospun nanofibres from different types of polymers with synthesized montmorillonite clays. Loading activated natural bentonite clay into any type of polymer can improve the adsorption property of electrospun nanofibres, but the bentonite clay must be well dispersed, suspended and loaded to achieve any benefit. This study may pave the way for further use of electrospun nanofibres loaded with clay in a wide variety of environmental and medical applications. Chapter 1 - The review presents data on the thermodynamic characteristics (heat capacity, enthalpy, entropy, and Gibbs function) in the region from 4 to 580 K cellulose acetates and cellulose nitrates with various degree of OH–groups substitution of cellulose with acetyl and nitro-groups, as well as the major plasticizers for these polymers, the temperatures of their relaxation and phase transitions, the effect of plasticizers on these characteristics of cellulose acetate and cellulose nitrate and the solubility of plasticizers in this polymers. On the basis of the data obtained, diagrams of the physical states of the cellulose acetate and cellulose nitrate – plasticizer systems were constructed and analyzed in a wide range of temperatures and throughout the concentration range of the components. Chapter 2 - Cellulose diacetate (CDA) has been used in the design of sorption matrices for the fluorescent analysis of polyaromatic and heterocyclic compounds. Physicochemical properties of CDA solutions in a binary acetone-water solvent were analyzed. The conditions of making film matrices from CDA with high sorption capacity for organic fluorophores, in particular pyrene, were optimized, namely: the solvent is an 95:5 acetone-water mixture, the polymer concentration is 3.6 wt.%, the dry casting method on a flat glass support. The morphologial, surfaceenergy, physicochemical and physicomechanical characteristics of our film CDA matrices in comparison with CDA fiber ones, commercial CDA membranes and cellulose sorption materials were examined. The possibility of using CDA matrices for solid-phase extraction and solid-

Preface

ix

surface fluorescence (SSF) of polycyclic aromatic hydrocarbons (PAH) and heteroaromatic compounds (eosin Y and trypaflavine) was investigated. The set of properties of our CDA film matrix (its opacity, smooth surface, fine-pore structure (0.2 ± 0.1 rel. un.), the pore size within 100−500 nm, the surface potential ξ = –32.0 ± 2.0 mV) was found to cause high sorption and fluorescence of pyrene in the solid phase of the sorbent. The fluorophore extraction degree was substantially higher than that for other sorbents. The effect of the concentration of various surfactants, namely, anionic (sodium dodecyl sulfate, SDS), cationic (cetyltrimethyl ammonium bromide, CTAB), and nonionic (polyoxyethylene (10) mono-4isooctylphenyl ether, TX-100), on pyrene fluorescence in aqueous micellar solutions before and after sorption concentration and in an adsorbed state on the CDA film was studied. The increased fluorescence intensity of pyrene on the solid-phase matrix is shown to be due to pyrene solubilization into surfactant hemimiceles formed on the sorbent surface. The highest degree of pyrene extraction on the CDA films was achieved in the presence of micelles of a cationic surfactant (CTAB). The influence of the solvent nature (acetonitrile, ethanol, dimethylsulfoxide, dioxane) and its concentration on the fluorescence intensity of pyrene sorbed on the CDA film from a water-organic solution was studied. Dimethylsulfoxide and ethanol were shown to be the most effective solvent additives for pyrene SSF. The maximum SSF signal of pyrene was found upon sorption from aqueous media containing 1.2−4.2 vol% of dimethylsulfoxide. A sorption-fluorimetric method to analyze PAH in aqueous media was developed on the basis of the obtained results. The possibility of reliable analysis on our solid-phase matrix in a concentration range of the fluorophore in the sorbate 2∙10–6 − 2∙10–8 g/L was shown with pyrene as an example. The detection sensitivity was fixed at a level of 2∙10–11 g/L, which corresponded to the maximum permissible concentration of the most toxic PAH (benzo(a)pyrene). The SSF technique with the CDA matrix is promising for use in environmental monitoring of PAH traces. Our developed polysaccharide matrices are characterized by relatively low cost, the ability of raw material reproduction and waste biodegradation, which is important for their use in test systems and rapid analytic methods.

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Calvin Roberson

Chapter 3 - Cellulose acetate (CA) is one of the most important esters of cellulose due to its renewable source, biodegradability, non-toxicity, low cost, and very poor flammability property. According to a recent report by Global Industry Analysis, the worldwide market of cellulose acetate is projected to about 1.05 million metric tons by 2017 and its estimated price is around $1.80/lb. Amongst the applications of CA are the manufacture of fibers, films, membranes, paints, plastics, cigarette filters, coats, textile, dialyzers, drugs, and biomedical utilities. The most traditional material resources for the industrial acetylation of cellulose are wood and cotton. However, regarding its availability in large amounts as a result of its widespread cultivation on a global scale, agricultural wastes have become an attractive renewable resource for the synthesis of cellulose acetate. Agricultural commodities are the key raw materials available to humanity for the sustainable production of numerous industrial and non-food consumer products, which led to the growing interest in the chemistry of compounds derived from biomass, and to exertions that aim at the use of agricultural wastes as alternative sources of chemicals, energy and materials. A positive feature of the trend in use of agricultural wastes, such as sugarcane bagasse, wheat and rice straw, cereal straws, and corn stove, as a feedstock for value-added products is that they are fairly free from wide price fluctuations, and are not subject to the debates about the use of agricultural food materials, as grains and cereals, for the production of chemicals, polymers, and materials, Furthermore, the concern about growth of CO2 emissions efforts led to the necessity to move toward green material solutions that fit into in the search of a sustainable development policy and low environmental impact resulting in the increase of investigations about the utilization of lignocellulosic materials as alternative sources of chemicals and energy. The major barriers to produce cellulose-based products from agricultural residues are the heterogeneity of the raw material, the experimental conditions reproducibility, the heterogeneous phase of the synthesis reaction, the difficulty of purification, the effluent disposal, and the control of the product quality. Chapter 4 - Incorporating activated bentonite clay (BC) into electrospun nanofibres is an established strategy for modulating adsorption

Preface

xi

behaviour. In the present study, we have provided a comprehensive review of electrospun nanofibres from different types of polymers with synthesized montmorillonite clays (MMT). Loading activated natural bentonite clay (BC) into any type of polymer can improve the adsorption property of electrospun nanofibres, but BC must be well dispersed, suspended and loaded to achieve any benefit. Naturally occurring calcium BC was completely activated to sodium BC with a 4 wt.% sodium carbonate (Na2CO3)/BC ratio. High throughput composite nanofibrous fabrics were produced from cellulose acetate (CA)/BC spinning solutions using free surface electrospinning and the effect of BC loadings on viscosity, surface tension and electrical conductivity prior to spinning were studied. It has been found that the higher the BC loading rate and thus higher viscosity and surface tension, the higher the applied voltage and the lower the rotation speed of the wires electrode were required in order to get the highest productivity accompanied with electrospinning stability. Chemical and thermal analyses were conducted on as-spun fibres, and SEM and TEM revealed a nanofibrous morphology consisting of an interpenetrating network of fibres and semi-spherical features resembling jellyfish with an internal core of BC. The problem with the existing adsorption process and the need for the change in the texture of the separation layer that controls the performance of the resultant membrane in terms of flux and selectivity were discussed and directed. We believe that this study may pave the way for further use of electrospun nanofibres loaded with clay in a wide variety of environmental and medical applications.

In: Cellulose Acetate Editor: Calvin Roberson

ISBN: 978-1-53614-704-9 © 2019 Nova Science Publishers, Inc.

Chapter 1

THERMODYNAMICS OF ACETATES AND NITRATES OF CELLULOSE AND THEIR PLASTIFICATION V. F. Uryash1,*, V. I. Pet’kov2, T. B. Khlyustova1, N. Yu. Kokurina1, V. N. Larina1 and K. V. Otvagina3 1

Lobachevsky State University of Nizhny Novgorod, Research Institute of Chemistry, Nizhny Novgorod, Russia 2 Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia 3 Nizhny Novgorod State Technical University n.a. R.E. Alekseev, Nizhny Novgorod, Russia

ABSTRACT The review presents data on the thermodynamic characteristics (heat capacity, enthalpy, entropy, and Gibbs function) in the region from 4 to 580 K cellulose acetates and cellulose nitrates with various degree of OH–groups substitution of cellulose with acetyl and nitro-groups, as well * Corresponding Author Email: [email protected].

2

V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al. as the major plasticizers for these polymers, the temperatures of their relaxation and phase transitions, the effect of plasticizers on these characteristics of cellulose acetate and cellulose nitrate and the solubility of plasticizers in this polymers. On the basis of the data obtained, diagrams of the physical states of the cellulose acetate and cellulose nitrate – plasticizer systems were constructed and analyzed in a wide range of temperatures and throughout the concentration range of the components.

Keywords: cellulose acetates, cellulose nitrates, plasticizers, thermodynamic characteristics, diagrams of the physical states

1. INTRODUCTION Cellulose takes the first place in abundance among all natural polymers [1, 2]. Various cellulose derivatives, in particular, cellulose acetates (CA) and cellulose nitrates (CN), are widely used as well. They act as raw materials in the production of smokeless powder, artificial fibres, insulating materials and films, varnishes and other products. However, the above-mentioned cellulose derivatives have high glass transition temperatures (Tg). For CA, Tg lies in the range of 370 – 490 K [3-8], and CN stays glassy up to a temperature of its thermal decomposition [4, 5, 8]. Therefore, in order to provide CA and CN, the required set of physicochemical and mechanical properties modification by plasticization is used. However, there is a noticeable gap between the theoretical (thermodynamic) basis of the plasticization processes and practice in polymer systems production. As noted in the paper by Hideo Sawada [9], any description of polymer synthesis that does not include thermodynamics is not complete, and consideration of specific systems without thermodynamics is impossible at all. In order to fill this gap, this review presents data on the thermodynamic characteristics (heat capacity, enthalpy, entropy, and Gibbs function) in the range from 4 to 580 K for CA and CN with various degree of OH–groups substitution of cellulose with acetyl and nitro–groups, as well as the major plasticizers for these

Thermodynamics of Acetates and Nitrates of Cellulose …

3

polymers, their relaxation temperatures and phase transitions temperatures, the effect of plasticizers on CA and CN properties and the solubility of plasticizers in this polymers. Based on the obtained data, phase diagrams for CA and CN – plasticizer systems were plotted and analyzed in a wide temperature range and in the entire concentration range of the components. These diagrams make it possible to determine the temperature and concentration limitations for the formation of homogeneous mixtures, i.e., true solutions of plasticizers in polymers and polymers in plasticizers, as well as two phases gels, where one of the solutions dispersed in a matrix of another as microdroplets. The comprehensive set of precision thermodynamic characteristics and physicochemical properties of CA and CN, as well as their interaction with plasticizers, constitute a theoretical basis for the development and optimization of technological processes for the CA and CN synthesis and their modification through plasticization.

2. THERMODYNAMICS AND PHYSICO-CHEMICAL ANALYSIS OF CELLULOSE ACETATES 2.1. Heat Capacity, Thermodynamic Functions and Relaxation Transitions of Cellulose Acetate of Various Degrees of Esterification The data on heat capacity, thermodynamic functions (enthalpy, entropy, and Gibbs function) and relaxation transitions of cellulose acetate with different degrees of substitution of the OH–groups of cellulose with acetyl groups are reported in [3, 6, 7]. The thermodynamic characteristics of the CA and CN were calculated on the molar mass of the repeating unit of the cellulose ester, taking into account the degree of substitution (conv. mol). The physicochemical characteristics of the analyzed CA samples are given in Table 2.1.

4

V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al. Table2.1. Physicochemical characteristics of the studied samples of cellulose acetate Cellulose acetate samples Content of the bounded acetic acid, mass% The degree of ОН–groups substitution The molar mass of CA the repeating unit, g/(conv. mol) The number of repeating units The ash content of the samples, mass% Reference

Triacetate (TAC)

Diacetate (DAC)

Monoacetate (MAC)

Diacetate (DAC)

60.4

54.5

43.7

55.8

2.85

2.40

1.70

2.47

281.70

262.80

233.40

265.74

300 0.04 [3, 7]

250 0.06 [3, 7]

250 0.05 [3, 7]

270 0.05 [6]

Figure 1. Temperature dependence of the heat capacity of the CA samples with different degrees of substitution: 1– 1.70 (MAC); 2 – 2.40 (DAC); 3 – 2.85 (TAC) [3, 7].

Heat capacity ( Cp ) was measured in the range 80–320 (560) K in adiabatic vacuum calorimeters. Adiabatic vacuum calorimeter design and method of operation are described in [2, 10, 11]. Measurement error of Cp was 0.3% [3, 7] and 0.5% [6] in the region of 80 – 320 K and 1% in the region of 320–560 K [3, 7]. In the research [6], DTA was also carried out in the region of 273 – 600 K of the cellulose diacetate (DAC) sample. The

Thermodynamics of Acetates and Nitrates of Cellulose …

5

CA samples were dried at 380 K and 0.6 Pa to a constant mass before the experiments. The obtained results are presented in Figure 1. From Figure 1 it can be seen, the heat capacity of the analysed samples increases monotonically with the temperature rise from 80 to 280 K. Several relaxation transitions appear on the curves Cp = f(Т) above 280 K. The transitions temperature was determined by the authors of [3, 7] from the kink of a curve So = f(T) [2, 10, 11]. The first transition was observed in the region of 280 – 310 K. The transition temperature depends insignificantly on the degree of cellulose OH–groups substitution with acetyl groups. The transition (Table 2.2) in the region of280 – 330 К was previously recorded by dielectric loss methods [12, 13], dilatometry [1329], thermomechanics [13, 18, 19] and NMR [12], at that the authors of [20] classified it as a β–transition. The authors of [13, 17] believe that it is due to the partial rupture of the intermolecular hydrogen bonds. Others [20] relate this transition to the appearance of the acetyl groups mobility. A similar transition in the region of 270–350 K was observed for cellulose [2, 21-64] and a number of its derivatives [2, 8, 12, 65-79]. With further heating of the analysed CA samples during the heat capacity measurement, a second transition of the endothermic nature appeared at the curves Cp = f(Т) in the region of 340 – 400 K. This transition corresponds to the devitrification of the polymer amorphous part (Тg1). Moreover, with an increase in the CA degree of substitution Tg1 increases from 368 K in the case of MAC to 393 K in the case of TAC. The third endothermic transition (Tg2) is observed on the curves Cp = f(Т) at 432, 420, and 398 K for TAC, DAC and MAC respectively. The authors of [19] consider that this transition is due to the disruption of bonds between the CA supramolecular structural elements and the emergence of their mobility. In particular, this transition was clearly observed in TAC and exist with the lowest intensity in MAC, because this process is super imposed on the crystallization of the MAC amorphous micro regions at 420 K. In DAC and TAC, the beginning of crystallization and a sharp decrease in the heat capacity is observed at 457 and 465 K, respectively. After the crystallization was completed, the endothermic transitions appeared on the

6

V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

curves Cp = f(Т)– the discontinuities in the heat capacity associated with the melting of the analysed CA. Moreover, in the MAC and DAC melting appeared in the form of a doublet at 488, 495 K (Figure 1, curve 1) and 500, 540 K (Figure 1, curve 2), respectively. A similar picture of melting was observed by the authors of [80, 81], who investigated low-substituted CA by DTA and DSC methods. The multiplicity of melting they explain by the chemical heterogeneity of the CA.

Figure 2. Isotherms of the CA heat capacity dependence on the content of BAA: ● – data [3, 7]; ▲ – data [6].

From the analysis of the literature data, it can be concluded that in the region of 290 – 560 K a number of relaxation and phase transitions appear in the CA. Temperatures of these transitions are given in Table 2.2. As can be seen from Table 2.2, a low-temperature transition (β–transition) is observed in the region of 283 – 333 K. The β–transition temperature depends both on the degree of cellulose OH–groups substitution by acetyl groups and on the research method. The CA devitrification occurs in two temperature ranges: 363 – 339 K and 398 – 483 K. This, apparently, is due to chemical heterogeneity and a different supramolecular structure of the CA. The CA crystallization (Tcr) and melting temperatures lie are in a relatively narrow interval: 446–465 K and 488–550 K, respectively. A

Thermodynamics of Acetates and Nitrates of Cellulose …

7

comparison (Figure 2) of the data on the molar heat capacity of the AC published in [3, 7] and [6], showed that there is a directly proportional dependence of their Cp on the content of bounded acetic acid (BAA) and they agree in the range from 80 to 150 K. At a higher temperature, the DAC Cp values from [6] lie above the Cp values for the TAC [3, 7]. Table 2.2. Temperatures of relaxation and phase transitions of cellulose acetates Characteristics of cellulose acetates Research The content The degree of method of BAA, OH–groups mass% substitution 51.9 2.20 62.4 2.99 62.4 2.99 53.4 2.30 62.4 2.99 52.3 2.23 Dilatometry 61.5 2.92 60.5 2.83 54.9 2.41 62.3 2.98 62.4 2.99 56.2 2.50 Thermo62.4 2.99 mechanics 62.0 2.96 Dielectric 52.0 2.21 55.8 2.47 43.5 1.69 39.4 1.47 DТА 54.1 2.35 61.9 2.95 56.2 2.50 DSC 60.4 2.85 54.5 2.40 Adiabatic calorimetry 43.7 1.70 55.8 2.47

Тβ, К

Тg1, К

Тg2, К

328 319 303 333 313 328 303 311 332 306 298 288

388 385 378 393 393 388 378 370 394 363 393 363

430

303 302

382

Тcr, К

428 445

463

435 408

457

Тm1, К

[16] [16] [14] [14] [15] [15] [20] [20] [20] [19] [13] [18]

465

[83]

463

[84] [12] [6] [80] [80] [85] [85] [81] [3, 7] [3, 7] [3, 7] [6]

480

495 503

453 485 511 490 312 302 287 302

393 380 368

Тm2, К Ref.

432 420 398

465 457 420

500 488

530 563 542

503 550 540 495

8

V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al. In Table 2.3 we demonstrate the data from the latest research because

the Cp measurement error in [6] is higher than in [3, 7]. To calculate the CA thermodynamic functions the authors of [3, 7] extrapolated the corresponding curves Cp = f(Т) to 0 K using the Kelly-Parks-Huffman equation [2, 8, 11]. At the same time, the missing heat capacity values of the CA samples in the region of 0 – 80 K were obtained similarly to the trend of the experimental curve Cp = f(Т) in the region 4 – 80 K for a cellulose nitrate sample (nitrogen content 11.9 mass%) [2, 8, 82].

2.2. Effect of the Degree of Esterification of Cellulose Acetate on Its Thermochemical Characteristics The analysis of the literature data in p. 2.1 shows that the CA heat capacity, thermodynamic functions, relaxation and phase transitions temperatures depend on the CA degree of substitution. As it was shown in [86], the degree of OH–groups substitution in cellulose with acetate groups also affects the CA standard enthalpy of combustion (ΔсНо) and formation (ΔfНо). The authors of [86] studied the same as in [3, 7] CA samples (Table 2.1). The CA enthalpy of combustion was determined in an improved B‒08MA calorimeter with a static calorimetric bomb [2, 8, 11, 87]. The calorimetric system calibration was carried out using reference benzoic, brand K‒2 (ΔUc = ‒26460.0 J/g when weighed on air). Energy equivalent of the system W = 14805±3 J/К with a doubled quadratic deviation from the mean result 0.02%. The CA was burnt in the form of tablets filled with molten paraffin and oxygen pressure of 3106Pa. According to the chromatographic analysis, the oxygen contained impurities, mol%: N2‒ 0.8; CO and CO2‒ 0.002; hydrocarbons‒ 0.001. The substance in a quartz crucible was ignited by discharging a capacitor onto a platinum wire connected to the substance using a cotton thread.

Thermodynamics of Acetates and Nitrates of Cellulose …

9

Table 2.3. Average heat capacity and thermodynamic functions of cellulose acetates containing 43.7 (1), 54.5 (2) and 60.4 (3) mass% BAA [3, 7] ( Cp and Sо(T)–Sо(0), J/К (conv. mol); Hо(T)–Hо(0) and Gо(T)–Gо(0), kJ/К (conv. mol)) Т, К

50 100 150 200 250 300 350 400 450 Т, К 50 100 150 200 250 300 350 400 450

Cp 1 50.78 118.9 164.0 203.5 233.2 290.2 336.9 442.9 425.0 Sо(T)–Sо(0) 1 20.96 80.13 137.0 189.9 238.7 285.6 333.1 385.5 437.8

Hо(T)–Hо(0) 2 58.57 138.1 186.0 226.1 267.2 306.0 373.8 458.3 478.2

3 67.02 142.2 189.2 229.4 270.2 312.2 396.8 480.5 512.7

2 24.09 92.55 157.9 217.1 271.9 324.0 376.2 431.6 486.8

3 29.96 103.3 170.3 230.4 286.0 338.8 393.7 451.7 509.9

1 2 0.7753 0.8916 5.245 6.065 12.33 14.21 21.57 24.53 32.53 36.86 45.45 51.17 60.88 68.14 80.59 88.93 102.8 112.4 –[Gо(T)–Gо(0)] 1 2 0.2727 0.3128 2.768 3.189 8.216 9.483 16.40 18.89 27.14 31.13 40.23 46.04 55.70 63.53 73.61 83.71 94.24 106.7

3 1.091 6.601 14.94 25.43 37.93 52.45 70.30 92.06 116.8 3 0.4058 3.727 10.60 20.64 33.57 49.20 67.49 88.61 112.7

Two resistance platinum thermometers and a digital voltmeter were used to measure the temperature rise and were included in the bridge circuit. The ratio of СО2 (experimental) to СО2 (calculated) in percent of weight for the analysed samples is 99.97–100.03%. Calculations in [86] were carried out for the following combustion reactions of MAC (1), DAC (2) and TAC (3): С9.2Н13.2О6.6 (s) + 9.2 О2 (g) → 9.2 CO2 (g) + 6.6 Н2О (l)

(1)

V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

10

С10.72Н14.72О7.36 (s) + 10.72 О2 (g) → 10.72 CO2 (g) + 7.36 Н2О (l)

(2)

С11.66Н15.66О7.83 (s) + 11.66 О2 (g) → 11.66 CO2 (g) + 7.83 Н2О (l)

(3)

The obtained standard values ΔcUо, ΔcHоиΔfHо for CA in a solid state at 298.15 Кarere presented in Table 2.4. As can be seen from Table 2.4, there is an increase in the ΔcHо and ΔfHо absolute value in the row MAC ‒TAC. Moreover, there is a directly proportional dependence of these thermochemical characteristics on the degree of OH‒groups substitution in cellulose with acetate groups (m), the mass fraction of the bounded acetic acid (Х, mass%) and the molar mass (М, g/(conv. mol)) of the CA repeating unit (Table 2.5). Table 2.4. Standard energy, enthalpy of combustion and formation of the CA samples at 298.15 К [86] Sample TAC DAC MAC

−ΔcUо,kJ/К (conv. mol) 5308.4±4.7 4890.2±6.6 4263.5±9.8

−ΔcHо,J/К (conv. mol) 5308.4±4.7 4890.2±6.6 4263.5±9.8

−ΔfHо,/К (conv. mol) 1518.0±4.9 1432.0±6.7 1243.3±9.9

Table 2.5. Coefficients а, b and R2 in approximation equations y= a + bx, where у = (–ΔcHо or –ΔfHо), х = (m, Х,М) [86] The argument (х) –ΔcHо, kJ/К (conv. mol) m Х, mass% М, g/(conv. mol) –ΔfHо, kJ/К (conv. mol) m Х, mass% М, g/(conv. mol)

a

b

R2

2903.4 1796.7 –363.75

847.11 57.748 20.15

0.9996 0.9963 0.9996

886.87 588.76 16.413

225.73 15.449 5.3689

0.9940 0.9986 0.9940

Thermodynamics of Acetates and Nitrates of Cellulose …

11

Figure 3. The dependence of the CA standard enthalpy of combustion on the degree of OH–groups substitution in cellulose with acetyl groups [86].

Figure 4. The dependence of the CA standard enthalpy of formation on the degree of OH–groups substitution in cellulose with acetyl groups [86].

As an example, Figure 3 and 4 show the dependencies ΔcHо = f(m) and ΔfHо = f(m). Table 2.5 includes the а and b coefficients in approximation equations y = a + bx. Similar dependences were observed for the CA physical transitions temperatures (β‒, α1‒, α2‒, crystallization and melting) and their thermodynamic characteristics (heat capacity (Figure 2), enthalpy, entropy, and Gibbs function) [3, 7].

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V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

3. THERMODYNAMICS AND PHYSICO-CHEMICAL ANALYSIS OF CELLULOSE NITRATES 3.1. Heat Capacity, Thermodynamic Functions and Relaxation Transitions of Cellulose Nitrate with a Different Content of Nitro Groups In the research [8, 82, 88, 89], a heat capacity was measured for cotton cellulose nitrate (CCN) with various degree of OH–groups substitution by nitro–groups (1.25, 2.23 and 2.64) and wood cellulose nitrate (WCN) containing 12.03 mass% of nitrogen [8, 37]. The Cp for CCN with 11.9 mass% of nitrogen was measured in the region of 4 – 400 K, and for other samples in the region of 80 – 350 K. The obtained experimental results are presented in Figures 5 and 6, and the averaged heat capacity values for the CCN with 11.9 mass% of nitrogen, together with the calculated thermodynamic functions – in Table 3.1.

Figure 5. The temperature dependence of the heat capacity of CCN with different content of nitrogen, mass%: 1 – 8.0; 2 – 11.9; 3 – 13.2 [8, 82].

Thermodynamics of Acetates and Nitrates of Cellulose …

13

The heat capacity was extrapolated to 0 K according to equation Cp = ВТ2 [2, 8, 11], where B = 8.84102 J/K mol, in order to calculate the thermodynamic functions (entropy, enthalpy and Gibbs function). The missing heat capacity values in the region of 0 -80 K for the CCN with 8.0 and 13.2 mass% of nitrogen, as well as the for WCN, were obtained by extrapolation the corresponding Cp = (Т) curves by the Kelly–Parks– Huffman equation [2, 8, 11] by analogy with the Cp = (Т) curve in the region of 0 – 80 K for the CN with 11.9 mass% of nitrogen [8, 82]. The CN heat capacity average values, as well as the calculated thermodynamic functions, are presented in Table 3.2. As could be seen from Figures 5, 6 and Table 3.1, 3.2, the CN heat capacity increases simultaneously with nitrogen content. The initial cellulose type also effects Cp of nitrates. In the studied temperature region, the WCN heat capacity is higher than one for the CCN with the same degree of substitution (Figures 5, 6 and Tables 3.1, 3.2). Thus, the WCN has a less ordered structure than the CCN.

Figure 6. Temperature dependence of the heat capacity (a) and the reduced heat capacity (b) of WCN containing 12.03 mass% of nitrogen [8, 37].

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V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

Table 3.1. The average heat capacity values and the thermodynamic functions of CCN, containing 11.9 mass% of nitrogen [2, 82] Т, К

Cp ,

5 10 20 40 60 80 100 120 140 160 180 200 220 240 260 280 298.15 300 320 340 360 370

J/K (conv. mol) 2.210 7.250 20.18 51.03 78.19 99.13 118.3 137.2 155.5 173.1 190.2 206.9 223.1 239.0 254.0 268.2 279.6 280.8 304.6 338.0 370.0 379.0

Ho(T)Ho(0), kJ/K (conv. mol)

So(T)So(0), J/K (conv. mol)

[Go(T)Go(0)], kJ/K (conv. mol)

0.00376 0.02697 0.1612 0.8821 2.183 3.963 6.135 8.690 11.62 14.90 18.54 22.51 26.81 31.43 36.36 41.59 46.52 47.08 52.92 59.33 66.44 70.19

1.105 4.117 12.91 36.66 62.65 88.11 112.3 135.5 158.0 179.9 201.3 222.2 242.7 262.8 282.5 301.9 318.9 320.8 339.7 359.1 379.4 389.7

0.00177 0.01421 0.09693 0.5841 1.576 3.086 5.092 7.571 10.51 13.89 17.70 21.94 26.59 31.64 37.10 42.94 48.56 49.17 55.78 62.76 70.15 73.99

The heat capacity of the analysed cellulose nitrates increases monotonically with arise of temperature up to 290 K. Then, an anomalous increase in the heat capacity associated with the relaxation transition is observed in the Cp =(Т) curves for CCN with 8.0 and 11.9 mass% nitrogen and for WCN. The transition temperature was determined by authors of [2, 82] from the kink of a corresponding So(T)–So(0) = (T) curve or from the Cp /Т = (T) dependence (Figure 6b). This transition cannot be attributed to the process of devitrification since the CN is glassy up to the decomposition temperature [90]. According to DTA data [91, 92] and optical studies [93] the CN decomposition temperature is 410 – 420 K. Attempts have been

Thermodynamics of Acetates and Nitrates of Cellulose …

15

made to determine the CN glass transition temperature by the direct dynamic mechanical analysis (DMA) [94, 95] as well as by extrapolating the Тg concentration dependence of CN mixtures with organic liquids [96100] to the zero concentration of the liquid component. According to these estimates, it is in the range of 400 – 440 K. As it was noted in p. 2.1, for cellulose there are data on the presence of several physical transitions with relaxation nature in different temperature regions [2, 21-64]. This is due to the microheterogeneity of its structure. Thus, in papers [22, 27, 30] by the dielectric method, it was established that ordered cellulose regions are devitrified at 490 – 500 K. Vitrification of amorphous cellulose regions occurring at 450 K was recorded by DMA [31]. Several secondary small-scale physical transitions were recorded for cellulose at temperatures below Тg. In [27, 32], for example, the transition at 180 – 200 K is associated with the mobility of the methyl group and the polarization of the primary hydroxyl in the electric field. The transition in the region of 273 – 310 K in cellulose and its derivatives is attributed to the appearance of pyranose rings vibrations around the glycosidic bond or to conformational changes of the “chair-bath” type on the level of the glucopyranose unit [21, 29, 34]. The authors of [8, 37, 82] carried out DTA for a number of CN samples (Figure 7). All samples exhibited a physical transition in the range of 300 – 350 K, with a simultaneous increase of the interval average temperature with a content of nitrogen (Figure 8, line 4). The type of initial cellulose subjected to nitration also affects the transition temperature. For WCN, it is 303 K (Figure 6b). The analysis of literature data showed that many authors have found a similar transition in CN using different methods (Table 3.3). Their interpretation of the transition nature and the dependence of its temperature on the nitrogen content in CN (Figure 8) is not uniform. As could be seen from Table 3.3, the results of the calorimetric, dilatometric methods and DTA are consistent and differ significantly from the data obtained by the dynamic mechanical method.

V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

16

Table 3.2. The average heat capacity values and thermodynamic functions of CCN containing 8.0 (1) and 13.2 (2) mass% of nitrogen, as well as WCN (3) [8, 37, 82] ( Cp and Sо(T)–Sо(0), J/К (conv. mol); Hо(T)–Hо(0) and Gо(T)–Gо(0), kJ/К (conv. mol)) Т, К 50 100 150 200 250 300 320 440 Т, К 50 100 150 200 250 300 320 440

Cp 1 48.77 97.01 142.8 182.7 222.5 258.0 282.0 ----Sо(T)–Sо(0) 1 35.49 84.54 132.8 179.3 224.3 268.0 285.5 ----

Hо(T)–Hо(0) 2 71.64 129.5 174.6 219.6 264.2 310.2 -------

3 67.41 118.5 162.2 204.5 243.7 289.0 309.5 327.9

2 54.75 123.5 184.6 240.9 294.6 346.8 -------

3 51.74 115.5 171.9 224.4 274.3 322.6 341.9 361.3

1 1.060 4.734 10.76 18.90 29.01 41.03 46.46 ---–[Gо(T)–Gо(0)] 1 0.7148 3.720 9.157 16.97 27.06 39.38 44.91 ----

2 1.605 6.728 14.34 24.18 36.26 50.62 ------2 1.132 5.619 13.35 24.00 37.39 53.44 -------

3 1.523 6.267 13.29 22.47 33.69 46.97 52.96 59.34 3 1.064 5.284 12.49 22.41 34.89 49.81 56.46 63.49

Figure 7. Thermograms of CN samples with different nitrogen content, mass%:1 – 13.2; 2 – 11.9; 3 – 10.5; 4 – 9.0; 5 – 8.0 [8, 82].

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17

Figure 8. The dependence of the physical transition temperature in CN on the nitrogen content. Data of the works: 1 – [101]; 2 – [95]; 3 – [17, 102]; 4 – [8, 82].

According to Uberreiter [101] (Figure 8, line 1) and Nakamura & Ookawa [95] (Figure 8, line 2), an increase in nitrogen content in CN leads to a decrease in the transition temperature. The first author believes that a decrease in the transition temperature is caused by the reduction of the interaction energy through hydrogen bonds in CN due to the partial OH– groups replacement in cellulose with ONO2–groups. This explanation is apparently not enough convincing since in the original cellulose a similar transition was observed at 273 K [106, 107]. Nakamura and Ookawa [95] explain the same phenomenon by a crystallinity increase in CN samples with a rise in the OH–groups substitution degree in cellulose with nitro–groups. However, from the later data obtained by Aziz & Shinouda [17] and Fujimoto & Inoue [102], the opposite picture is observed: with a rise of nitrogen content in CN, the transition temperature increases (Figure 8, line 3). This corresponds to our findings (Figure 8, line 4). According to the author of [97], the activation energy of this transition in CN is approximately three times less than the CN glass transition activation energy. Cellulose acetates (p. 2.1) also exhibit a temperature increase of a similar transition with a rise in the degree of OH–groups substitution in cellulose with acetate groups. The authors of [101, 103, 104] assign it to a second–order transition. Aziz &

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18

Shinouda [17], who studied this transition in cellulose mononitrate, refer it to the disrupture of bridge hydrogen bonds between non-esterified OH– groups in CN macromolecules. Japanese researchers [95, 101] classify it as a –transition (a relaxation process occurring in a disordered part of the polymer and associated with the mobility of macromolecules’ individual sections which are smaller than segments of the polymer chain [108, 109]). Table 3.3. Physical transition temperature in cellulose nitrate Cellulose nitrate characteristics Nitrogen content, Mol. mass mass.% 13.0 ---9.6 ----

Research method

Transition temperature, К

Transition interpretation

329 324

Vitrification Vitrification Second–order transition

[101] [101]

333

–transition

[95]

338

–transition

[95]

–transition Disruption of bridge hydrogen bonds

[95]

325.7

Reference

12.0

----

13.3

28300

11.9

21000

10.8

24800

343

6.6

----

298

11.94 ---13.3

42100 ---28300

318 273 238

–transition ---–transition

[102] [94] [95]

11.9

21000

256

–transition

[95]

10.8

24800

268

[95]

12.0

----

11.95

63000

–transition Second–order transition Relaxation of ОН– groups Relaxation of ОNО2– groups

Dilatometry

Dynamic mechanical

Gravimetry

339 298

Dielectric 11.95

63000

8.0

38000

9.0 10.5

27300 51200

11.9

73000

13.2

75000

358 Calorimetry, DTA DTA DTA Calorimetry, DTA DTA

308 310 316 320 324 324 332

[103]

[17]

[104] [105] [105] [8, 82]

Disorder of structured microregions CN

[8, 82] [8, 82] [8, 82] [8, 82]

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19

Thus, the analysis of data presented in the literature indicates that the –transition observed in cellulose nitrates with different substitution degree can be attributed to the disordering of the CN microregions, and the rise in nitrogen content leads to an increase in the microregions degree of ordering. The thermodynamic functions comparison for CN with different degree of substitution (Tables 3.1 and 3.2) shows that with rise in substitution (m) degree of cellulose OH–groups with ONO2–groups, the values of heat capacity, entropy, enthalpy and Gibbs function (Figure 9) increase linearly. This type of dependence appears to be due to the increase in the atoms number in the CN repeating unit as a result of the OH–groups replacement by nitro–groups and, thereby, the number of atomic vibrations that contribute to the heat capacity of the polymer. There are data on the heat capacity of cellulose in the literature [25, 35, 107, 110, 111]. The most reliable, in our opinion, are the results given in [35], since the heat capacity was measured in a vacuum adiabatic calorimeter in the range of 80 – 400 K with an error of 0.5%, and the averaged values of Cp together with the thermodynamic functions are presented in the form of a table. Exactly these values are represented on the axis for pure cellulose (Figure 9). The CA thermodynamic characteristics dependence on the OH–groups substitution degree by acetate groups has a similar form (Figure 2). The obtained dependences of the CN thermodynamic characteristics on m and temperature are described by equations (4) – (6), which allow to calculate CN Cp (J/K (conv. mol)), enthalpy (kJ/ (conv. mol)) and entropy (J/ K(conv. mol)) with any substitution degree in the region of 80 – 320 K with an error of 1%.

Cp =–(34.879–25.532m)+(1.135–0.05637m)T–(0.00102–0.000279m)T2 (4) S0(T)–S0(0) = –(27.975–8.567m) + (0.745+0.2314m)T – 0.0002368mT2 (5)

20

V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al. H0(T)–H0(0)= – (0.9657 + 0.3016m) + (0.00101 + 0.01503m)T + + (0.0003701 + 0.00002766m)T2

(6)

Figure 9. The dependence of the heat capacity (a), entropy (b), enthalpy (c), and Gibbs function (d) on the OH–groups substitution degree (m) in cellulose with ОNO2–groups at temperatures, К: 1 – 50; 2 – 100; 3 – 200; 4 – 300 [8].

3.2. Effect of the Content of Nitro Groups in Cellulose Nitrate on Its Structure With nitrogen content increase in CN, not only physicochemical properties of polymers change, but also a structure. This is confirmed by microscopic studies of CCN and WCN with different substitution degree

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21

(Figures 10, 11) [2, 8, 37, 82, 112]. From Figure 10 it can be seen that the particles of CN with low substitution degree (8.0% of nitrogen) have an irregular clump shape (Figure 10a) and consist of globular formations, with the average size of 90 nm (Figure 10b). The structure of the other two samples is fibrillar (Figures 10c, e), with the transverse size 70 nm in case of 11.9% nitrogen (Figure 10d), and 40 nm in case of 13.2% nitrogen (Figure 10f). Thus, with an increase in the OH-groups substitution degree in cellulose, the CCN structure changes from globular to fibrillar i.e., become more ordered. The same conclusion was reached by the authors of papers [113-115], who studied the change in cellulose structure during nitration by X–ray diffraction and IR spectroscopy. They showed that as OH–groups are replaced by esters, the cellulose initial fibrillar structure is disrupted first, and then a new, ordered structure is gradually formed in CN. Not only the CN nitrogen content affects its structure, but also the type of a feedstock. The WCN structure with 12% nitrogen is fibrillar (Figure 11), as well as CCN with the same substitution degree (Figure 10), however, the diameter of microfibrils in the WCN is larger – 80 nm.

4. HEAT CAPACITY AND THERMODYNAMIC FUNCTIONS OF PLASTIFICATORS FOR CELLULOSE ACETATES AND NITRATES 4.1. Nitrates of Glycerol, Di- and Triethylene Glycol Nitroglycerin (NGC), di- (DEGDN) and triethylene glycol dinitrate (TEGDN) are used for technical purposes as explosives [116, 117] and in medicine [118]. They are used as plasticizers for CN in the gunpowders manufacture [8, 89, 116]. For a purposeful use of these compounds, it is necessary to know their heat capacity, thermodynamic functions, as well as temperatures of their relaxation and phase transitions. The thermodynamic characteristics of these nitro compounds have been studied in a wide temperature range in research works [8, 119-121]. The analysed NGC,

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V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

DEGDN and TEGDN were qualified as “pure.” Their basic physicochemical properties are presented in Table 4.1. The values, within the limits of measurement error, are consistent with the literature data [116, 122, 123]. The results of nitroesters’ elemental analysis corresponded to the formula composition with the error of the method (0.5%).

Figure 10. Microphotographs of CCN samples (a, c, e – in optical, b, d, f – in electron microscopes) containing nitrogen, mass%: a, b – 8.0; c, d – 11.9; e, f – 13.2 [8, 82].

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23

Figure 11. Micrograph of WCN microfibrils with nitrogen content 12.03 mass% [8, 37].

Table 4.1. The main physicochemical characteristics of nitroesters [8, 119-121] Nitroesters d(293)103, kg/m3 nD293

Composition, mass%

293, сPl C H O N

Calculated Found Calculated Found Calculated Found Calculated Found

NGC 1.5900 1.4739 35.5 15.86 15.79 2.21 2.06 63.42 63.15 18.51 18.30

DEGDN 1.4846 1.4512 8.18 24.50 24.32 4.11 4.12 57.11 57.35 14.28 14.21

TEGDN 1.3270 1.4531 11.4 30.01 29.51 5.04 5.23 53.29 54.06 11.66 11.20

The experimental data on glycerol trinitrate heat capacity in the range of 80 – 320 K are presented in Figure 12 [8, 119], and the corresponding averaged values in Table 4.2. With cooling at a rate of 0.2 – 0.3 K/sec, the liquid NGC vitrified. The heat capacity of the glassy NGC increased monotonically up to 180 K.

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V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

Figure 12. The temperature dependence of glycerol trinitrate heat capacity: 1 –glassy, 2 – labile crystals; 3 – liquid [8, 119].

A sharp rise on the curve Cp = f(T) in the range of 180 – 200 K is related to the devitrification. The glass transition temperature, determined graphically from the bend point on the entropy temperature dependence curve in the region of devitrification [2, 10, 11], is 1951 К, from the state of the supercooled liquid, a slow process of NGC crystallization begin around 220 K. In the interval 220 – 274 K the heat capacity of the supercooled liquid was measured by the authors of [8, 119] during the stepwise cooling of the calorimetric ampoule with NGC in this temperature range. With multiple crystallization, they obtained only labile crystals that were stable (under the conditions of the calorimetric experiment) throughout the temperature range below the melting point. This is confirmed by the data of a number of authors [116, 122, 124-131], who studied NGC thermal behaviour. It was also established in [124-131] that it can easily be supercooled and difficult to crystallize. Under special conditions (for example, in a presence of some additives), NGC crystallizes in two monotropic modifications: labile and stable. The crystalline form of the labile isomer belongs to the triclinic system and the stable isomer to the bipyramidal–rhombic one.

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25

Table 4.2. The averaged values of the heat capacity and the thermodynamic functions of the glassy and liquid NGC, as well as NGC labile crystals the heat capacity [8, 119] Т, К Glassy 0 5 10 20 30 40 60 80 100 120 140 160 180 Liquid 200 220 240 260 280 298.15 320

C p ,J/К mol

Ho(T)Ho(0), kJ/К mol

So(T),J/К mol

[Go(T)Ho(0)],kJ/К mol

0 0.4822 4.122 20.69 40.25 57.99 86.69 110.2 126.2 141.0 154.4 167.5 181.8

0 0.0005 0.0103 0.1281 0.4325 0.9258 2.358 4.365 6.734 9.406 12.36 15.58 19.07

38.00 38.11 39.34 46.83 58.90 72.97 102.2 130.5 156.8 181.2 203.9 225.4 245.9

0 0.1901 0.3830 0.8085 1.335 1.993 3.745 6.073 8.950 12.33 16.19 20.48 25.20

343.7 348.2 350.5 353.6 358.4 364.3 372.9

23.57 30.51 37.50 44.53 51.65 58.20 66.26

Т, К

C

 , p

J/К mol

Т, К

C p , J/К mol

80 109.5

100 125.7

200 191.2

220 206.3

269.5 302.6 332.9 361.1 387.5 410.2 436.2 Labile crystals 120 140 139.0 151.4 240 223.3

260 240.0

30.33 36.05 42.41 49.35 56.84 64.09 73.33 160 164.5

180 177.3

275.3 253.0

Sapozhnikov & Snitko [130], after analyzing the literature data, came to the conclusion that NGC in a liquid state can exist as two chemical isomers – and. In a later work [132], NGC labile and stable forms are considered respectively as cis– and trans–isomers. Melting of labile NG crystals was observed in the range of 240 – 255 K (Figure 12) [8, 119]. A significant temperature range of labile crystals pre-melting can be explained by a presence of different isomers in the liquid NGC. The

26

V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

presence of a small number of trans–isomers will cause irregularities in the crystal lattice structure of the labile form. Surface effects may also play aspecific role. The melting temperature of labile crystals was determined by the authors of [8, 119] from the dependence of the equilibrium temperature on the reciprocal of the melt fraction of the weighed sample [10, 11]. The melting point of the analysed sample was Т’m = 274.6 К and absolutely pure substance Тom = 275.30.3 К. A close Тm value of NGC labile crystals (275.9 K) was given in [116].The labile crystals enthalpy of melting (mHo)is 20.130.15 kJ/mol (the average result of three experiments).The entropy of melting (mSo = 73.12  0.50 J/K mol) was calculated, assuming that the process is isothermal [8, 119]. Calorimetrically [10, 11], by depression of the melting point (ТomТ’m = 0.7 К), it was found that the total content of impurities soluble in the liquid phase in the analysed NGC sample was 2.2 mol% [8, 119]. To calculate the thermodynamic functions (Table 4.2), the obtained dependence C p = f(T) for glassy NG was extrapolated to 0 K by the Kelly– Parks–Huffman method [2, 8, 11]. Glassy glycerin was chosen as a reference substance and its the heat capacity was experimentally measured in the range of 2 – 300 K [133, 134]. So(0) of glassy NGC was calculated.  Cp (Тg) = 152 J/К mol, Т2 = 151 К, and So(0) = 38 J/К mol. DEGDN heat capacity was measured in a vacuum adiabatic calorimeter in the range of 80 – 320 K [8, 120]. The obtained experimental results are presented in Figure 13, and the corresponding averaged values in Table 4.3 [120]. When the liquid DEGDN was cooled in a calorimeter at a rate of 0.2 – 0.3 K/sec, it vitrified (Tg = 1831 К). The data on the DEGDN ability to crystallize upon cooling in two monotropic forms: labile (KII) and stable (KI) with melting points of 262 and 275 K, respectively, are reported in [116, 117, 135, 136]. Depending on the crystallization conditions, the authors of [8, 120] obtained two different DEGDN crystal modifications, which were stable up to the melting points of these crystalline forms. When Cp of the supercooled liquid DEGDN was measured at 200 K, its crystallization

Thermodynamics of Acetates and Nitrates of Cellulose …

27

began (Figure 13, curve 1). In this case, with prolonged exposure of the sample under adiabatic conditions, we obtained KI crystal form (Figure 13, curve 2). If the cooling of liquid DEGDN was carried out from room temperature to 220 K and then the sample was slowly heated to 230 K, it crystallized into the KII modification (Figure 13, curve 2/). The heat capacity of each of these forms was well reproduced in several experiments on crystallization and the transition of one form to another [8, 120] was not observed. As is customary [10], crystalline modifications were marked as KI and KII in the order corresponding to a decrease in the melting points. It was noted [8, 120] that after melting of the KI form, the “memory” effect typical for organic crystals appear. It was necessary to heat the molten sample up to 320 K and hold at this temperature for 12 hours so that when cooled, it crystallized in the KII modification. The temperatures and enthalpies of melting of both DEGDN crystalline forms were determined. Special experiments have been carried out to determine melting points by the known method [10, 11] according to the graph of the equilibrium temperature dependence on the reciprocal of the melt fraction of the weighed sample. The melting points of the analysed sample crystals Т/m and the absolutely pure substance Тom (Тom(KI) = 276.50.1 K; Тom(KII) = 263.50.1 K) were obtained. These melting points values were obtained by a reliable calorimetric method. They are 1 – 2 K above the corresponding estimated literature data [116, 117, 135, 136]. The enthalpy of melting (mНo) was measured by the method of continuous input of energy into the calorimeter [10, 11]. Three experiments were carried out for each crystal modification. The results: mНo(KI) = 25.40.2 kJ/mol; mНo(KII) = 21.60.2 kJ/mol; mSo(KI) = 91.90.7 J/К mol; mSo(KII) = 82.00.8 J/К mol. Calorimetrically [10, 11], according to the depression of the melting temperature of the КI (ТomТ’m = 0.2 K) crystal form, it was established that the total content of impurities (soluble only in the liquid phase) in the studied DEGDN sample was 0.8 mole%.

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Table 4.3. The averaged values of the heat capacity and the thermodynamic functions of the crystalline (KI) and liquid DEGDN, as well as its heat capacity in crystalline (KII), glassy and supercooled liquid states [8, 120] Т, К

C p , J/К mol

Crystal I 10 20 30 40 60 80 100 120 140 160 180 200 220 240 260 276.5 Liquid 276.5 280 298.15 320

Нo(Т)–Нo(0), kJ/mol

So(T), J/К mol

–[Go(T) –Ho(0)], kJ/mol

2.657 14.91 30.87 47.93 76.88 99.70 115.4 128.6 141.0 153.0 165.2 177.0 189.2 200.7 212.4 222.0

0.0068 0.0874 0.3151 0.7095 1.967 3.746 5.903 8.349 11.05 13.99 17.17 20.59 24.25 28.15 32.28 35.86

0.8739 5.968 14.98 26.21 51.32 76.74 100.7 123.0 143.8 163.4 182.1 200.1 217.6 234.5 251.0 264.4

0.0020 0.0320 0.1344 0.3389 1.112 2.393 4.171 6.412 9.082 12.16 15.61 19.44 23.61 28.13 32.99 37.24

344.0 344.0 344.0 344.0

61.26 62.47 68.66 76.23

356.3 360.6 382.0 406.5

37.24 38.50 45.18 53.86

Т, К

C p , J/К mol

Cristal II 80 100 120 140 160 180 200 220 240 263.5 Glass 80 100 120 140 160 180 183

99.70 115.4 127.9 139.5 151.2 162.9 175.0 187.5 200.8 216.2 101.2 117.7 132.5 146.7 160.9 186.0 240.0

Supercooled liquid 200 220 260

350.0 349.6 344.0

As could be seen in Figure13, in the 120 – 240 K interval the heat capacity of KI crystals (curve 2) by 0.2 – 1.4% lies above the corresponding data for KII (curve 2/). From the data obtained [8, 120] on the heat capacity of two crystalline forms, it is difficult to make a simple conclusion about the nature of the DEGDN polymorphism. Cp measurements from 80 K make it impossible to obtain such information from an analysis of the Gibbs function temperature dependence. Unfortunately, the necessary information on the structure of DEGDN

Thermodynamics of Acetates and Nitrates of Cellulose …

29

crystal modifications and the molecules conformations in crystals is also missing. To calculate the thermodynamic functions obtained in [8, 120], the Cp = f(T) dependence of the crystal I was extrapolated from 80 to 0 K by the Kelly–Parks–Huffman method [2, 8, 11], crystalline 1,4-butanediol was chosen as a reference substance, due to the presence of reliable data on the heat capacity from 5 K for it in the literature [137]. The thermodynamic functions of the crystalline and liquid DEGDN are presented in Table 4.3. So(0) of the glassy DEGDN [8, 120], was calculated as described in [10, 11]:  C p (Тg) = 173 J/К mol, Т2 = 130 К, а So(0) = 20 J/К mol. TEGDN heat capacity was measured in the range of 80 – 320 K (Figure 14) [8, 121]. Its averaged values are presented in Table 4.4. The authors of [8, 121] failed to crystallize TEGDN in the calorimetric experiment. There are also no published data on TEGDN crystallization [116, 138]. Therefore, only one physical transition appeared in TEGDN

Cp = f(T) curve (Figure 14) in the interval 180 – 200 K corresponding to devitrification (Тg = 1901 К). It was noted in [8, 121] that the heat capacity of liquid TEGDN decreases immediately after devitrification with increasing temperature. This may be due to the fact that at temperatures close to Tg, liquid TEGDN is associated. In this case, when heated (during the measurement C p ), two quantities contribute to the observed heat capacity: the regular C p value and the constituentconditional by the destruction of the associates. The last constituent changes from the maximum value at 200 K to zero at Т corresponding to the minimum value on the Cp = f(T) curve of the liquid. A similar phenomenon was observed, for example, in some alkyl compounds of selenium and tellurium [139141]. To calculate the thermodynamic functions, the authors of [8, 121] extrapolated the obtained Cp = f(T) dependence of glassy TEGDN from 80 to 0 K by the Kelly–Parks–Huffman method [2, 8, 11]. Glassy glycerine was used as a reference substance for which reliable data on the heat capacity in the interval 2 – 300 K is available in the literature [133, 134].

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V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

In [8, 121], Sо(0) of glassy TEGDN was calculated, as described in [10, 11].  Cp (Тg) = 242 J/К mol, Т2 = 136 К, а So(0) = 42 J/К mol. In Table 4.5 thermodynamic functions are given under standard conditions and the vitrification characteristics of the studied nitro [8, 119-121].

Figure 13. The temperature dependence of DEGDN heat capacity: 1 –glassy; 2 – crystals II; 2/– crystals of I; 3 – liquid [8, 120].

Figure 14. The temperature dependence of TEGDN heat capacity: 1 – glassy; 2 – liquid [8, 121].

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Table 4.4. Averaged values of the heat capacity and thermodynamic functions of glassy and liquid TEGDN [8, 121] Т, К Glass 5 10 20 40 60 80 100 120 140 160 180 Liquid 200 220 240 260 280 298.15 300 320

C p , J/К mol

Нo(Т)–Нo(0), kJ/mol

So(T)–So(0), J/К mol

–[Go(T)–Go(0)], kJ/mol

0.5393 4.788 24.37 66.95 101.3 127.3 147.0 165.2 182.6 202.3 222.0

0.000655 0.01221 0.1508 1.080 2.774 5.072 7.820 10.94 14.42 18.25 22.44

0.1745 1.608 10.42 40.91 74.78 107.7 138.2 166.7 193.4 219.0 243.6

0.000217 0.003874 0.05761 0.5566 1.713 3.540 6.003 9.055 12.66 16.78 21.41

464.0 463.0 456.4 449.0 442.0 438.3 438.0 435.0

29.38 38.65 47.85 56.91 65.81 73.80 74.61 83.34

279.8 324.1 346.1 400.3 433.3 461.0 463.7 491.8

26.59 32.64 39.53 47.18 55.52 63.64 64.49 74.05

4.2. Phthalic Acid Esters It is known that plasticization is one of the most common methods of polymer modification [2, 4, 8, 142-145], which is used to lower their glass transition temperature and expand the temperature range of the rubbery state. Phthalic acid esters are the most common plasticizers of CA and CN [4, 5, 142, 145]. The thermodynamic characteristics of dimethyl– (DMPh), diethyl– (DEPh), dibutyl– (DBPh), and di-(2-ethylhexyl)phthalate (DOPh) were studied in [4, 146-152]. The listed phthalates were qualifications “pure.” They were additionally purified by fractionation under reduced pressure, as recommended in [153]. Fractions with characteristics listed in

V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

32

Table 4.6 were collected, which correspond to reliable literary data [142, 153]. Table 4.5. Thermodynamic functions under standard conditions (Т = 298.15 К) and vitrification characteristics of the studied nitro compounds [8, 119-121] Nitro ethers М, g/mol

NGC 227.1

DEGDN 196.1

TEGDN 240.2

C p , J/К mol

364.3

344.0

438.3

Н (Т)–Н (0), kJ/mol So(T)–So(0), J/К mol –[Go(T)–Go(0)], kJ/mol Тg, К

58.20 410.2 64.09 195

68.66 382.0 45.18 183

73.80 461.0 63.64 190

 C p (Тg), J/К mol

152

173

242

Т2, К So(0), J/К mol

151 38

130 20

136 42

o

o

Table 4.6. The physical properties of o-dialkylphthalates Phthalates DMPh DEPh DEPh DBPh DOPh

293, g/сm3 1.1898 1.1184 1.123 1.0466 0.9838

nD293 1.5158 1.5019 --1.4928 1.4868

293, сPl 13.93 13.24 --20.96 79.39

Reference [146, 150] [146] [147] [146, 148, 149] [146, 149]

In the early work [146], the heat capacity of DMPh, DBPh, and DOPh was measured in vacuum adiabatic calorimeters in the range of 60 – 300 K with an error of 0.3% [2, 8, 11], and in the 300 – 360 K interval with an error of 0.5% [8, 11, 154]. There are more recent precision studies [149, 150], in which the dependence Cp = f(T) for DBPh and DOPh was measured in the range of 10 – 300 K, and DMPh in the range of 6 – 120 K. The heat capacity of DEPh is also measured in a vacuum adiabatic calorimeter [147] in the range of 10 – 360 K. In the 10 – 50 K interval, with an error of 0.5% and 0.1% in the 50 – 360 K interval.

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Figure 15. The temperature dependence of phthalates heat capacity: 1 – DMPh [146, 150], 2 – DEPh [147]. Physical states of phthalates: g – glass, c – crystal, l – liquid.

The results obtained by various authors are presented in Figures 15 and 16 and in Tables 4.7 – 4.9. As can be seen from Figures 15 and 16 and Tables 4.7 – 4.9, under conditions of a calorimetric experiment only DMPh [146] and DEPh [147] were crystallized. The other studied phthalic acid esters only vitrify during cooling. In Table 4.10 the vitrification and melting characteristics of the mentioned dialkylphthalates are given. As it can be seen from Table 4.10, the glass transition temperatures of dialkylphthalates obtained calorimetrically [146152] and the DTA method [88, 155] agree well with each other. Their Tg dependence on the number of СН2–groups in alkyl radicals passes through a minimum for DBP. A similar dependence is also observed for the viscosity (Table 4.6). However, a minimum is accounted for by DEPh. According to the authors of [146], this is explained by the fact that the orientational and dispersion energies (the main terms of the intermolecular interaction energy) vary in the range of these dialkyl phthalates in opposite directions.

V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

34

Table 4.7. The averaged values of the heat capacity of glassy, supercooled liquid and liquid DBPh and DOPh [149] C p Т, К

J/K mol 1

2 Glassy 10 6.515 10.14 20 31.17 43.26 40 75.52 107.1 60 114.2 163.0 80 147.7 213.6 100 177.4 256.6 120 204.4 296.0 140 231.0 332.2 160 256.5 367.9 170 281.0 389.0 Supercooled liquid and liquid 190 428.5 632.9 210 428.9 638.0 230 434.9 646.4 250 444.4 659.0 270 457.0 675.7 290 470.7 694.6 298.15 476.0 704.7 300 477.0 706.9

Hо(T)–Hо(0) kJ/mol

Sо(T)–Sо(0) J/K mol

–[Gо(T)–Gо(0)] kJ/mol

1

2

1

2

1

2

0.01645 0.2032 1.284 3.190 5.815 9.072 12.89 17.24 22.12 24.79

0.02559 0.2915 1.809 4.522 8.294 13.01 18.56 24.84 31.84 35.62

41.22 53.19 88.88 127.0 164.5 200.7 235.4 268.9 301.5 317.7

62.45 79.57 129.6 183.9 237.8 290.2 340.7 389.0 435.7 458.6

0.3957 0.8606 2.271 4.430 7.345 11.00 15.36 20.41 26.11 29.22

0.5989 1.300 3.375 6.512 10.73 16.01 22.32 29.62 37.87 42.35

32.70 41.26 49.89 58.68 67.69 76.97 80.82 81.70

45.20 57.92 70.76 83.80 97.16 110.8 116.6 117.9

361.5 404.3 443.6 480.2 514.8 548.0 561.1 564.1

511.6 575.3 633.6 688.0 739.4 788.3 807.7 812.1

35.99 43.64 52.12 61.35 71.33 81.95 86.46 87.51

52.00 62.87 74.98 88.20 102.5 117.8 124.3 125.8

Figure 16. The temperature dependence of phthalates heat capacity: – DBPh [146, 149], 2 – DOPh [146, 149]. Physical states of phthalates: g – glass, l – liquid.

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Table 4.8. The averaged values of the heat capacity and the thermodynamic functions of glassy, crystalline, and liquid DMPh [146, 150] Т, К

C p ,

Ho(T)Ho(0), kJ/К mol

J/К mol Glassy 10 6.040 0.02031 20 21.30 0.1540 40 51.62 0.8919 60 78.64 2.202 80 98.90 3.986 100 116.6 6.141 120 134.1 8.647 140 150.0 11.49 160 163.4 14.63 180 178.5 18.04 Crystalline 10 3.701 0.00995 20 16.69 0.1070 40 46.50 0.7419 60 74.12 1.954 100 116.0 5.795 140 149.2 11.14 180 173.2 17.59 220 192.5 24.93 260 207.5 32.92 274.16 213.5 35.90 Supercooled liquid and liquid 274.16 294.6 52.85 280 296.6 54.57 298.15 303.1 60.01 320 310.2 66.71 340 317.1 72.98 360 323.8 79.4

So(T), J/К mol

[Go(T)Ho(0)], kJ/К mol

19.9 28.6 53.0 79.1 104.7 128.6 151.4 173.3 194.2 214.3

0.1787 0.4180 1.228 2.544 4.390 6.719 9.521 12.77 31.06 20.53

1.134 7.554 28.40 52.60 100.7 145.5 185.8 222.7 255.5 267.0

0.00139 0.0441 0.3941 1.202 4.275 9.230 15.85 24.06 33.51 37.30

328.8 335.1 353.9 375.6 394.6 412.9

37.29 39.26 45.50 53.48 61.18 69.24

The first decreases, and the second increases with the elongation of the alkyl radical. Therefore, in the beginning, the predominant influence has the decrease in the orientational energy, and then the increase in the dispersion energy prevails. The crystallization of DMPh from the state of a

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V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

Table 4.9. The averaged values of the heat capacity and the thermodynamic functions of glassy, crystalline, and liquid DEPh [147] Т, К

Cp , J/К mol

Ho(T)Ho(0), kJ/К mol

Glassy 10 6.44 0.0260 20 24.80 0.1810 40 61.95 1.056 60 91.44 2.601 80 116.1 4.683 100 137.5 7.224 120 156.9 10.17 140 175.6 13.49 160 195.1 17.20 Crystalline 10 5.91 0.0148 20 23.84 0.1592 40 62.12 1.030 60 91.64 2.580 100 136.3 7.188 140 170.9 13.35 180 202.1 20.81 220 233.8 29.53 260 269.9 39.56 Supercooled liquid and liquid 190 331.3 33.05 200 332.6 36.37 220 336.6 43.06 240 342.3 49.84 260 349.4 56.76 280 357.8 63.83 298.15 366.1 70.34 320 377.0 78.52 340 387.3 86.16 360 397.8 94.01

So(T), J/К mol

[Go(T)Ho(0)], kJ/К mol

24.57 34.56 63.42 94.33 124.1 152.4 179.2 204.8 229.5

0.2197 0.5102 1.481 3.059 5.245 8.016 11.33 15.18 19.52

14.97 11.27 39.91 70.93 128.8 180.3 227.1 270.7 312.5

0.0049 0.0661 0.5664 1.676 5.693 11.89 20.06 30.02 41.68

270.1 287.1 319.0 348.5 376.1 402.3 425.1 451.3 474.5 496.9

18.26 21.05 27.11 33.79 41.04 48.83 56.34 65.91 75.17 84.89

supercooled liquid occurs at 217 K. In [150], a distinction was made between the heat capacity of glassy and crystalline DMPh in the range from 6 to 106 K. Moreover, Cp of glassy DMPh is higher than the one of crystalline. This difference is 39% at 10 K and decreases with increasing

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37

temperature. In the 110 – 130 K interval, the heat capacities of the glass and the crystal are practically the same, and above 130 K the Cp value of glassy DMPh is again higher than the Cp of crystal. A similar behaviour is observed for DEPh [147]. In this paper, it is noted that there is no universal relation for the heat capacity of the substance in the glassy and crystalline states. The authors of [149, 150] calculated the zero entropy of the studied phthalates. So(0) turned out to be equal, J/K mol: 16.8 for DMPh, 39 for DBPh and 59 for DOPh. The calculation of the DMPh melting enthalpy resulted in mНo = 16.94 ± 0.04 kJ/mol [146]. According to the depression of Tm, the authorsof [146] calculated the mole fraction of the impurity (N2) in the DMPh sample, which turned out to be 0.01 mol, and Tоm = 274.18 K (Table 4.10). The corresponding values for the DEPh are: mНo = 17.984 ± 0.003 kJ/mol and Tоm = 269.92 ± 0.02 K (Table 4.10), N2 = 0,0012 mol in DEPh sample [147]. The difference in the heat capacity of tempered and annealed glassy DEPh samples was found in [147]. The authors of [147] calculated the excess entropy of glassy DEPh at absolute zero So(0) and obtained 23 J/K mol for tempered glass and 20 J/K mol for annealed glass. Table 4.10. Vitrification and melting characteristics of o-dialkylphthalates Phthalates

Tg, K

Tоm, K

DMPh DMPh DMPh DMPh DEPh DBPh DBPh DBPh DOPh DOPh

192.0 193 192 193 180.8 173.5 176 181 182.5 184

274.18 ---273 274 269.92 ----------------

mНo,kJ/ mol 16.94 ---------17.98 ----------------

Method of research Calorimetry DTA DTA DTA Calorimetry Calorimetry DTA DTA Calorimetry DTA

Reference [146] [155] [88] [6] [147] [146, 148, 149] [155] [8] [146, 149] [155]

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V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al.

4.3. Triphenyl Phosphate The heat capacity of triphenyl phosphate (TPP) [6, 156] was measured in the range of 12 – 340 K in a vacuum adiabatic calorimeter [2, 8, 11] with an error of – 1% below 20 K, 0.5% in the range of 20 – 50 K and 0.3% above 50 K. The sample of TPP studied in [6, 156] was qualified as “pure.” It was additionally fractionated under vacuum at 2.67 kPa and a fraction boiling at 533 K was collected [142]. The content of the main substance in this fraction of TPP, determined calorimetrically by the depression of the melting point, was 99.7 mol%. The obtained experimental Cp values of TPP are presented in Figure 17, and its averaged values, together with thermodynamic functions, in Table 4.11. Before the measurement, the sample was cooled in the calorimeter at a rate of 0.1 – 0.2 K/s starting from 345 K. Wherein, the TPP was crystallizing (Figure 17).

Figure 17. The temperature dependence of TPP heat capacity: c – crystalline; l – liquid [6, 156].

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39

During the measurement, C p the heat capacity of the TPP monotonically increased up to 305 K. Then, a sharp rise and a brake are observed on the curve C p = f(T) due to the melting of the substance. The melting points of the sample studied in [6, 156] and absolutely pure TPP, calculated from the experimental data, are correspondingly 322.44 ± 0.01 К and 322.55 ± 0.01 К. There is a value of Tm(TPP) = 322.4 Кin the literature [157], which agrees well with the calorimetric data. By the method of continuous input of energy into the calorimeter under adiabatic conditions, the melting enthalpy of TPP (mНo = 29.61 ± 0.20 kJ/mol) was determined. Assuming the melting process to be isothermal, the melting entropy mSo = 91.84 ± 0.60 J/K mol was calculated. In DTA experiments [6], it was possible to vitrify TPP (Тg = 212 ± 2 K). After devitrification, the TPP crystallized at 217 K and then melted (Tm = 322 К). Table 4.11. The averaged values of the heat capacity and the thermodynamic functions of crystalline and liquid TPP [6, 156] Т, К

Cp

,J/К mol

Crystalline 10 7.590 20 30.49 40 75.55 60 103.8 100 141.8 140 178.6 180 220.2 220 265.4 260 311.0 300 356.2 322.44 381.6 Liquid 322.44 475.3 330 475.9 340 476.8

Ho(T)Ho(0), kJ/К mol

So(T), J/К mol

[Go(T)Ho(0)], kJ/К mol

0.0254 0.2041 1.295 3.112 8.044 14.44 22.40 32.11 43.64 56.98 65.25

3.876 15.38 51.39 87.33 150.0 203.5 253.3 301.8 349.8 397.5 424.1

0.0133 0.1034 0.7609 2.158 6.955 14.04 23.18 34.29 47.32 62.27 71.47

94.86 98.47 103.2

515.9 527.0 541.2

71.47 75.43 80.78

40

V. F. Uryash, V. I. Pet’kov, T. B. Khlyustova et al. Table 4.12. The averaged values of the heat capacity and the thermodynamic functions of the glassy, crystalline, and liquid TA [7, 158]

Т, К

Cp , J/К mol

Glassy 10 3.039 30 42.80 50 93.40 70 119.3 90 138.8 110 157.0 130 173.1 150 187.7 170 202.0 Supercooled liquid 200 364.3 220 367.9 240 370.4 260 374.5 Crystalline 10 2.838 30 41.50 50 81.10 90 134.2 130 173.1 170 201.5 210 225.5 250 251.8 275.1 268.6 Liquid 275.1 378.0 300 384.7 320 390.5

Ho(T)Ho(0), kJ/К mol

So(T), J/К mol

[Go(T)Ho(0)], kJ/К mol

0.0077 0.4268 1.810 3.957 6.540 9.503 12.81 16.42 20.31

41.03 59.99 94.13 130.0 162.4 192.1 219.7 245.5 269.8

0.4026 1.373 2.807 5.143 8.076 11.63 15.75 20.41 25.55

27.26 34.58 41.96 49.42

307.2 342.1 374.3 406.1

34.18 40.68 47.87 55.65

0.0072 0.4085 1.648 6.063 12.24 19.74 28.28 37.84 44.37

0.9552 19.07 49.85 113.3 169.4 219.8 264.8 306.4 331.3

0.0024 0.1636 0.8445 4.134 9.782 17.63 27.33 38.76 46.77

70.22 79.72 87.47

425.3 458.3 483.3

46.77 57.77 67.19

4.4. Triacetin The heat capacity of triacetin (TA) [7, 158] was measured in the range of 9 – 320 K in a vacuum adiabatic calorimeter [2, 8, 11] with an error of ~1% below 30 K and TX-100. The energy transfer efficiency increased with increasing surfactant concentration. The maximum (fourfold) increase in fluorescence was observed in the presence of anionic SDS micelles.

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Figure 13. Relative fluorescence intensity of pyrene (IFl Rel) in aqueous surfactant solutions before (1) and after (2) the sorption column step, and on a CDA (3) or C (4) film after solid-matrix sorption by using SDS (a), CTAB (b), and TX-100 (c).

Next, the effect of the surfactant concentration on the fluorimetric analysis of pyrene was estimated. Figure 13 shows the relative fluorescence intensities of pyrene in aqueous surfactant solutions before and after the sorption column step, on CDA and, for comparison, on C after sorptional concentration. The relative fluorescence intensity (IFl Rel) of pyrene in solution was calculated as I5/1000, where I5 is the maximum IFl value of the fifth vibronic band of the spectrum. The IFl Rel of CDAadsorbed pyrene was calculated as I5/I5 (CMC2), and that of C-adsorbed pyrene as I5/I5 (CMC1), where I5 (CMC2) and I5 (CMC1) are the I5 values for pyrene on the solid-phase matrix after the dynamic sorption from the aqueous micellar surfactant–pyrene solutions with СS = CMC2 and CMC1, respectively. These surfactant concentrations were chosen because the fluorescence intensity of pyrene was maximum under given experimental conditions.

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The IFl Rel, as well as the IFl, depends on the surfactant concentration in the system and increases with increasing СS (Figure 13, columns 1). This situation remains when surfactants in the concentration range CMC2–2 CMC2 are used. As an example, Figure 13 b shows data for CTAB–pyrene at ССТАВ = 2 CMC2. At higher surfactant concentrations, the IFl Rel value decreased. Figure 13c gives an example for TX-100–pyrene at СТХ-100 = 5 CMC2.

(a)

(b)

(c)

(d)

Figure 14. SEM images of the CDA film surface after sorption of CTAB (a, b), SDS (c), TX-100 (d) micelles with solubilized pyrene at СS = CMC2 (a, c, d) and 2 CMC2 (b).

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After sorption concentration of the surfactants from their aqueous micellar media, the relative fluorescence intensity of pyrene declined significantly in all solutions (Figure 13, columns 2). This indicates that surfactant micelles were adsorbed on the CDA film. This may be due to pyrene solubilization in surfactant hemimicelles (aggregates of micelles) formed on the sorbent surface. Visualization of the aggregates formed on the CDA film surface after sorption concentration of the aqueous micellar pyrene solutions is shown in Figure 14. The SEM images of the surface of the original CDA film were discussed in Subsection 1.3 (Figure 5a, b). Then we examined pyrene fluorescence on CDA films after preliminary solid-phase concentration of the PAH in its micellar microphase (Figure 13, columns 3). As in the surfactant–pyrene solutions, the relative fluorescence intensity of pyrene on the films increased with increasing СS. The maximum signal intensity of pyrene on the film was observed at concentrations close to CMC2. For SDS–pyrene, CTAB– pyrene, and TX-100–pyrene, the IFl Rel peaked at CSDS = 5 CMC1 –CMC2, ССТАВ = CMC2 – 2 CMC2, and СТХ-100 = CMC2, respectively. Almost at the same concentrations, the signal intensity of pyrene on the solid-phase matrix became higher than that for the initial solution. With further increase in СS, the IFl Rel of pyrene in the CDA phase decreased. When C was used, the relative intensity of pyrene fluorescence peaked at СS = CMC1 (Figure 13, columns 4). The surfactant concentration in the systems and their nature significantly influenced the degree of pyrene extraction from aqueous solution (Table 9). Under the adopted experimental conditions, the highest R value of pyrene after its sorption concentration from micellar solutions on CDA was recorded at CS = CMC1 – 2 CMC2, whereas it was found only at a concentration equal to CMC1 in the case of C. The PAH sorption degree in the C phase was always lower than that in the CDA phase. The highest extraction degree was observed after sorption concentration of pyrene from CTAB micellar solutions on CDA. This suggests that CTAB micelles with solubilized pyrene molecules, having a positive charge localized at the interface between micellar micropseudophase and aqueous phase, adsorb better to the negatively

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S. M. Rogacheva, A. B. Shipovskaya and T. I. Gubina

charged surface of the film (ξ = −31.5 ± 2.5 mV, Table 3), in comparison with SDS and TX-100 micelles. The relatively high values of R (above 50%) for sorption concentration on CDA from aqueous micellar solutions of the negatively charged SDS with CSDS = CMC1 – CMC2 could be explained by a charge exchange (a change in the sign of the electric potential) on the polymer matrix surface owing to surfactant anion adsorption. A similar change in the sign of the electric potential from negative to positive with transition through the isoelectric state was described [54] for cellulose fibers (initial and CDAcoated) in solutions of low-molecular-weight and high-molecular-weight surfactants. When the nonionic TX-100 was used, a pyrene extraction degree of 50% was obtained only at СТХ-100 = CMC2. However, when using a lower pyrene concentration (0.2 μM) and СТХ-100 = 10 mM (Table 8), the pyrene extraction degree reached 84%, and an SSF signal of the highest intensity was obtained on the CDA films (Figure 11c). Table 9. Degree of pyrene extraction from aqueous surfactant–pyrene solutions during sorption concentration on solid-phase matrices Surfactant

СS (mM)

CMC

SDS

0.08 0.8 8 40 50 0.09 0.9 21 42 0.02 0.2 1.4 7.5

0.01 CMC 1 0.1 CMC 1 CMC 1 5 CMC 1 CMC 2 0.1 CMC 1 CMC 1 CMC2 2 CMC 2 0.1 CMC 1 CMC 1 CMC2 5 CMC 2

СТАВ

ТХ-100

R, % CDA film 27 ± 2.1 48 ± 2.2 58 ± 2.2 60 ± 2.0 57 ± 1.9 37 ± 3.0 50 ± 3.5 72 ± 3.0 95 ± 3.3 14 ± 2.2 27 ± 2.1 50 ± 2.0 32 ± 2.0

Cellulose 7 ± 1.9 30 ± 4.4 50 ± 4.0 4 ± 1.1 – – 27 ± 4.0 21 ± 4.6 20 ± 4.5 – – – –

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It is noted that the degree of pyrene extraction by the cellulose matrix under similar conditions is much lower. The commercial CDA membrane exhibits no sorption concentration of pyrene from aqueous micellar media. Our experimental results show that CDA films exhibit a high ability to adsorb SDS, CTAB, and TX-100 micelles with solubilized pyrene. In aqueous micellar media at CS = 0.01 CMC1 – 2 CMC2, pyrene fluorescence increases by 2–4 times. The use of organized media lowers the polarity index of pyrene in working solutions, which can be explained by a decrease in the probability of non-radiative transitions owing to a decrease in the polarity of the nearest PAH microenvironment. Sorption concentration of pyrene from aqueous micellar media on CDA is accompanied by the formation of surfactant hemimicelles with solubilized pyrene on the sorbent surface. This raises the “stiffness” of the fluorescent centers and significantly enhances the fluorescence intensity of the PAH on the solid-phase matrix. The maximum fluorescence signal of pyrene on CDA films is obtained at surfactant concentrations close to CMC2. Thus, the highest degree of pyrene extraction was achieved by using micellar solutions of the cationic CTAB. Under the adopted experimental conditions, the sorption degree decreased in the row CTAB → SDS → TX-100. The solid-phase sorption of pyrene on CDA films from aqueous micellar solutions can be used for its quantitative analysis by SSF [58].

4. SOLVENT EFFECT ON THE SORPTION AND SOLID-SURFACE FLUORESCENCE OF PYRENE ON CELLULOSE DIACETATE FILMS The solvent nature is known to exert a great influence on the efficiency of sorption [32, 59, 60] and fluorescence [25, 61–64] of most substances. Therefore, the effect of the solvent nature and its concentration on the sorption and fluorescence of pyrene on CDA matrices was investigated [65].

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Table 10. Physical properties* of the solvents used and their toxicity LD50, mg/kg [66] Water 100.0 1.000 78.3 5.9 1.000 − 1.17 − Ethanol 78.3 0.7893 24.55 5.8 0.654 − 0.83 10300 Acetonitrile 81.6 0.7875 35.94 11.8 0.460 0.31 − 2460 DMSO 189.0 1.1004 46.46 13.5 0.444 0.76 − 20 000 Dioxane 101.3 1.0330 2.21 1.5 0.164 0.37 − 5170 *The values given by Reichardt [32]: T is the boiling point, ρ the density, εr the dielectric constant, μ the dipole moment, ЕTN the empirical parameter of the solvent polarity, β, α the Kamlet–Taft solvatochromic parameters (β is the hydrogen bond acceptor ability, α the hydrogen bond donation ability). Solvent

T, °C

ρ, g/cm³

εr

μ∙1030, C∙m

ЕT N

β

α

Pyrene solutions in water-organic media with concentrations 10–6, 10–7 and 10–8 М were used in our experiments. Stock pyrene solutions were prepared in solvents with various physical properties [32] (Table 10). The solvent concentration in the most concentrated aqueous pyrene solution was 0.2 vol%. The choice of these solvents was due to pyrene and other PAH being soluble in them and their ability to mix with water. Figure 15 compares the SSF intensities of pyrene on the CDA film after sorption from the water-organic solvent systems. It can be seen from the diagram that with a pyrene content of 10–8 М the solvent has little effect on the SSF intensity. At a pyrene concentration of 10–7 М, the SSF intensities differ, depending on the solvent nature, and the strongest fluorescence signal was detected in the case of DMSO. At a pyrene concentration of 10−6 М, the highest SSF signal was detected in the waterethanol medium. It follows from the data obtained that when using DMSO and ethanol, high fluorescence intensities of pyrene were observed. Moreover, these solvents are the least toxic (Table 10) [66], so they are more preferable in analytical practice. The influence of the solvent concentration (ethanol and DMSO) in the sorbate on the SSF intensity of pyrene was estimated. To this end, pyrene was sorbed from its 0.1 μМ aqueous solutions with various solvent

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contents onto CDA films and the fluorescence spectra of the probe in the solid phase of the matrices were recorded. It has been established that the SSF intensity of pyrene is the highest when the content of both solvents in the aqueous media is 1.2−4.2 vol% (Table 11), but the SSF intensity of the pyrene signal in the presence of DMSO is 1.7 times (on the average) higher than that in the case of ethanol.

Figure 15. Fluorescence intensity (IFl) of pyrene on the CDA matrix when sorbed from aqueous media with concentrations of 1 μM (1), 0.1 μM (2), and 0.01 μМ (3), containing various organic solvents: acetonitrile, ethanol, dimethylsulfoxide, and dioxane. IFl is measured at λem = 394 nm, λex = 320 nm.

Pyrene solvation in DMSO apparently leads to more efficient concentration of the probe on the hydrophobic CDA matrix. Analysis of the reference data presented in Table 10 has shown that DMSO has a higher dielectric constant and a higher dipole moment than ethanol, but judging by the empirical parameter ЕTN, its polarity is much lower; besides, it is a hydrogen bond acceptor (β = 0.73), while ethanol is a hydrogen bond donor (α = 0.86), i.e., it is a protic solvent. It is known that when solvent mixtures are used, selective solvation of the substance proceeds, i.e., the formation of a shell from the molecules of the preferred solvent near every solute molecule [32]. Pyrene is a hydrophobic (non-polar) compound, with

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a planar molecule with electron density distributed throughout [67]. In aqueous media, DMSO, owing to its chemical structure and physical properties (εr, μ), is a more effective solvating agent for pyrene than ethanol. In an aqueous solution, the solvation shell made of DMSO molecules has its own micro-polarity, which probably affects the processes of pyrene sorption. It is also possible that the hydrogen bond acceptor ability of DMSO due to the S=O group determines the efficiency of concentration of the probe on the matrix surface, since the monomeric unit of cellulose diacetate contains hydroxyl groups (hydrogen bond donors). Additional research is required to explain the discovered phenomenon. It should be noted that an increased (above 20%) DMSO content in the aqueous medium leads to a change in the CDA film properties, which negatively affects the results of SSF analysis. Thus, DMSO seems to be the most effective solvent for pyrene when sorption from an aqueous medium onto a CDA film, the optimum range of DMSO concentrations in aqueous media being 1.2−4.2 vol%. Table 11. Fluorescence intensity of pyrene sorbed onto CDA matrices from aqueous media containing the solvent with several concentrations Solvent concentration in the sorbate, vol%

IFl of pyrene (λex = 320 nm, λ em = 394 nm) in the solid phase after sorption from the aqueous medium containing: Ethanol

DMSO

0.2

72.3 ± 4.1

80.2 ± 5.0

1.2

121.2 ± 5.5

204.3 ± 7.4

2.2

109.7 ± 6.3

195.4 ± 6.1

4.2

114.4 ± 5.1

188.5 ± 6.6

6.2

104.2 ± 4.1

150.1 ± 7.3

10.0

92.5 ± 3.6

132.2 ± 5.4

15.0

87.0 ± 5.2

126.5 ± 5.3

20.0

83.6 ± 6.3

98.1 ± 6.2

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5. QUANTITATIVE PYRENE ANALYSIS IN MODEL AQUEOUS SOLUTIONS USING SOLID-SURFACE FLUORESCENCE To assess the possibility of quantitative PAH analysis in aqueous media, we studied the fluorescence intensity of pyrene in the sorbent phase as depends on its concentration in aqueous solutions containing 1.2 vol% of DMSO as an additive to dissolve PAH. The pyrene concentration range was extended to 2·10−11 – 2·10−6 g/L (10–13 – 10–8 М) [65]. Dynamic sorption of pyrene from solution on the CDA matrices was performed by passing 10 ml of the solution through a sorption column (Figure 7 a) at least five times at a rate of 1 drop/s. The films with PAH were dried, after which the SSF spectra of pyrene were recorded in the range λ = 350–450 nm at λexc = 320 nm. The dependence IFl = f(–lgC) shown in Figure 16 was plotted from the maximum of the fifth peak of the pyrene fluorescence spectrum at λem = 394 nm (Figure 9). Figure 16 shows that the semi logarithmic concentration dependence has a linear character in the range of 2∙10−6 − 2∙10−8 g/L. When the pyrene concentration in the sorbate decreased down to 2∙10−11 g/L, the SSF signal intensity had very low values and varied little. With further reduction in the pyrene concentration, the signal on the matrix was not detected, i.e., the detection limit of pyrene was 2∙10−11 g/L (10−13 M).

Figure 16. Dependence of the fluorescence intensity (IFl) of pyrene on CDA matrices on the logarithm of its concentration (2·10-11 – 2·10-6 g/L) in a water-DMSO solution (1.2 vol.%). IFl is measured at λem = 394 nm, λex = 320 nm.

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Figure 17. Calibration graph of the dependence of the fluorescence intensity (IFl) of pyrene on CDA matrices on the logarithm of its concentration (2∙10 −6 − 2∙10−8 g/L) in a water-DMSO solution (1.2 vol.%). IFl is measured at λem = 394 nm, λex = 320 nm.

For quantitative pyrene analysis, a calibration graph was plotted in the concentration range 2∙10−6 – 2∙10−8 g/L (Figure 17). Table 12 presents the results of the statistical processing of the experimental data. Thus, we plotted the dependence of the SSF signal on the pyrene concentration in the sorbate, it had a linear character in the range 2∙10−6 – 2∙10−8 g/L (pyrene), the detection sensitivity of the substance was 2∙10−11 g/L, which is below the maximum permissible concentration of the most toxic PAH (benzo(a)pyrene) in drinking water. Consequently, the application of our CDA matrices and the SSF analysis conditions allows analyzing PAH traces in environmental objects [68]. Table 12. Statistical processing of the experimental data (Figure 17) С, g/L

–lg С, [g/L]

2∙10-6 10-6 2∙10-7 10-7 2∙10-8

5.7 6.0 6.7 7.0 7.7

X (IFl) 17.47 13.37 8.87 7.17 5.02

σ

N

d

р

2.12 1.97 1.87 1.51 1.43

10 10 10 10 10

1.31 1.22 1.15 0.93 0.89

0.05 0.05 0.05 0.05 0.05

Note: С the concentration of pyrene; X (Mean) is the arithmetic mean of the values of IFl; σ the standard deviation; N the sample size; d the confidence interval; р the critical level of significance.

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Since pyrene is an analogue of benzo[a]pyrene, this method of analysis can be proposed for screening water samples for the toxicant, followed by its quantification in positive samples using conventional HPLC or GC-MS techniques. In this way, it is possible to simplify and significantly reduce the cost of the routine procedures adopted in environmental monitoring.

6. A TECHNOLOGICAL SCHEME FOR THE PREPARATION AND APPLICATION OF TEST SYSTEMS BASED ON CELLULOSE DIACETATE MATRICES According research results, we propose a basic technological scheme for obtaining and applying test systems on CDA matrices for PAH analysis in aqueous media (Figure 18).

Figure 18. A technological scheme of obtaining and applying test systems based on CDA films for PAH analysis in aqueous media: 1 - CDA powder, 2 – a polymer doser, 3 – a water doser, 4 – an acetone dispenser, 5 – a mixer, 6 – a casting support for a CDA film, 7 - cutting the CDA film into samples, 8 – the analyzing solution with PAH, 9 - a sorption column with a CDA sample, 10 – a fluorescent spectrometer, 11 output of the fluorescence spectra to a computer display.

Below are the principal stages of the preparation of CDA matrices, their use for PAH sorption from aqueous media, and the SSF of analyte on the matrix:

S. M. Rogacheva, A. B. Shipovskaya and T. I. Gubina

182        

CDA dissolution in an acetone-water mixture, casting a film matrix by pouring the resulting solution onto a glass substrate, cutting the CDA film onto 1 × 1 cm samples, preparation of the PAH solution to be analyzed, dynamic sorption of the analyte on the CDA matrix in the sorption column, placing the matrix into a holder for solid samples, recording the fluorescence spectra of PAH in the sorbent matrix on a fluorescent spectrometer, and quantification of the characteristics (fluorescence intensity, polarity index, PAH extraction degree, etc.).

The PAH analysis method developed by us has an increased sensitivity and informativeness, since it allows one to preconcentrate the analytes on the sorbent, to simplify sampling and to conduct analysis directly in the sorbent phase [69]. It is applicable for the analysis of both aqueous media and other environmental objects, for example, soil, sludge, as well as food (fats). The analysis of any object (except aqueous media) requires preliminary PAH extraction with a solvent (e.g., DMSO) followed by the preparation of an aqueous medium for sorption. Additional research is needed to optimize the conditions of sampling in every specific case.

CONCLUSION In order to develop sorption matrices made from cellulose diacetate, we analyzed the physicochemical properties of polymer solutions in the binary acetone-water solvent. It has been established that introduction of small water amounts into acetone improves its thermodynamic quality as a solvent for CDA, reduces the viscosity of casting solutions, influences the hydrodynamic behavior of macromolecules and determines the porosity of solid-phase cellulose acetate structures. The conditions of casting film

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matrices from CDA with high sorption capacity relative to organic fluorophores, in particular pyrene, have been optimized, namely: the solvent is an 95:5 acetone-water mixture, the polymer concentration is 3.6 wt.%, the dry casting method on a flat glass surface. The morphology, surface-energy, physicochemical and physicomechanical characteristics of our film CDA matrices in comparison with CDA fiber ones, commercial CDA membranes and cellulose sorption materials were studied. The possibility of using CDA matrices as platforms for solid-surface fluorescence of adsorbed fluorophores was discovered for the first time. It has been established that our CDA fiber matrices can be used for solidphase extraction of hydrophilic heteroaromatic compounds, CDA film matrices are very effective in analyzing trace amounts of PAH (ecotoxicants). The set of valuable properties of our CDA film matrices (their opacity, smooth surface, fine-pore structure (0.2 ± 0.1 rel. un.), the pore size within 100-500 nm, the surface potential ξ = –32.0 ± 2.0 mV) was noted to cause high sorption and fluorescence of PAH in the solid phase of the sorbent. The fluorophore extraction degree was shown to be substantially higher than that of other sorbents, in particular, the cellulose matrix. Addition of small amounts of dimethylsulfoxide or a surfactant to the PAH (sorbate) solution analyzed allowed us to significantly increase the sorption efficiency of the substance and the intensity of its fluorescence in the sorbent phase. As a result, a method to analyze PAH in aqueous media by solidsurface fluorescence on CDA matrices was developed. With pyrene as an example, the possibility of reliable analysis of the substance on our solidphase matrix in a concentration range of the fluorophore in the sorbate 2∙10–6 – 2∙10–8 g/L was shown. The detection sensitivity was fixed at a level of 2∙10–11 g/L, which corresponded to the maximum permissible concentration of the most toxic PAH (benzo(a)pyrene). The research conducted gives evidence of the prospects of using our CDA sorbents in environmental monitoring of PAH, as well as in pharmacological and toxicological studies. The designed polysaccharide matrices are characterized by relatively low cost, the ability of raw material

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reproduction and waste biodegradation, which is important for their use in test systems and rapid analytic methods.

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[56] Crans, D.C., Rithner, C.D., Baruah, B., Gourley, B.L., and Levinger, N.E. 2006. “Molecular Probe Location in Reverse Micelles Determined by NMR Dipolar Interactions.” Journal of the American Chemical Society 128:4437–45. [57] Beltyukova, S., Teslyuk, O., Egorova, A., and Tselik, E. 2002. “Solid-phase luminescence determination of ciprofloxacin and norfloxacin in biological fluids.” Journal of Fluorescence 12:269– 72. [58] Strashko, A.V., Rogacheva, S.M., Gubina, T.I., Shipovskaya, A.B., and Mel’nikov, A.G. 2016. A sorption-fluorimetric method for the analysis of polycyclic aromatic hydrocarbons in aqueous solutions and a sorbent for the implementation of the method. Patent RF 2,581,411. [59] Dyachuk, O.A. Gubina, T.I., Khatuntseva, L.N., and Melnikov, G.V. 2006. “The luminescent investigations of the processes of pyrene sorbtion on modified cellulose and foamed polyrethane.” Izvestiya Vysshikh Uchebnykh Zavedeniy. Khimiya Khimicheskaya Tekhnologiya 49(2):45–8; in Rus. [60] Kolotilov, P.N., Polunin, K.E., Polunina, I.A., and Larin, A.V. 2010. “Effect of component ratio of binary organic solvent on sorption of phenols by silica.” Colloid Journal 72:499–503. [61] Kononenko, L.I., Bel'tyukova, S.V., Meshkova, S.B., Kravchenko, T.B., and Poluktov, N.S. 1978. “Effect of solvents on ratio of intensities of luminescence bands of terbium and dysprosium ions in solutions of complexes with acetoacetic ester.” Translated from Zhurnal Prikladnoi Spektroskopii 28:1013–7. [62] Wrobel, D., Hanyz, I., and Bartkowiak, R. 1998. “Ion Fluorescence and time-resolved delayed luminescence of porphyrins in organic solvents and polymer matrices.” Journal of Fluorescence 8:191–8. [63] Bagrovskaya, N.A., Nikiforova, T.E., and Kozlov, V.A. 2002. “Influence of solvent acidity on equilibrium sorption of Zn(II) and Cd(II) by cellulose-based polymers.” Russian Journal of General Chemistry 72:345−8.

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[64] Khakhalina, M.S., Tikhomirova, I.Yu., and Puzyk, M.V. 2010. “Effect of vapors of water and organic solvents on the luminescence of cation exchange membranes immobilized with cyclometalated Pt(II) complexes.” Optics and Spectroscopy 108:703–9. [65] Rogacheva, S.M., Volkova, E.V., Otradnova, M.I., Gubina, T.I., and Shipovskaya, A.B. 2018. “Solvent Effect on the Solid-Surface Fluorescence of Pyrene on Cellulose Diacetate Matrices.” International Journal of Optics 2018:6. Article ID 3012081. Accessed June 11, 2018. doi:10.1155/2018/3012081. [66] Lazarev, N.V., and Levina, E.N., ed. 1976. Harmful substances in industry. A reference book for chemists, engineers and doctors. V. 1. Organic substances. Leningrad: Chemistry; in Rus. [67] Pankratov, A.N., Uchaeva, I.M., Rogacheva, S.M., and Volkova, E.V. 2016. “Spatial and electronic structure of the pyrene molecule, tripaflavin cation and eosin anions as a prerequisite for interpreting their solid-phase fluorescence.” Izvestiya of Saratov University. New Series. Series: Chemistry. Biology. Ecology 16:393−8; in Rus. doi:10.18500/ 1816-9775-2016-16-4-393-398. [68] Rogacheva, S.M., Shipovskaya, A.B., Volkova, E.V., Khurshudyan, G.N., Suska-Malawska, M., and Gubina, T.I. 2018. “Solid-state surface luminescence of polycyclic aromatic hydrocarbons adsorbed on cellulose diacetate matrices.” Proceedings SPIE 10716:20-1–6 Accessed April 26, 2018. doi:10.1117/12.2314855. [69] Strashko, A.V., Gubina, T.I., Rogacheva, S.M., Shipovskaya, A.B., and Volkova, E.V. 2018. A sorption-fluorimetric method for quantitative analysis of polycyclic aromatic hydrocarbons in aqueous solutions. Patent RF 2,647,475.

BIOGRAPHICAL SKETCHES Svetlana M. Rogacheva Affiliation: Nature & Technosphere Safety Department, Yuri Gagarin Saratov State Technical University

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Education: 1983–1988 - Saratov State University, Chemistry Faculty. 4-monthly course of “Physico-chemical methods in molecular biology” in the Center of the Biological Research of the Academy of Sciences of USSR (Puschino) 1994–1997 - Post-graduate course in Biochemistry, Biophysics and Physiology Department, Saratov State University, Saratov, Russia. 1998 - Candidate of biological sciences (=Ph.D.) in the specialties “Microbiology” and “Biochemistry”. 2009 - Doctor of biological sciences in the specialty “Biophysics”. Business Address: 77 Politechnicheskaya St., 410054 Saratov, Russian Federation Research and Professional Experience: 1988–2001 - Microbial enzymes catalyzing the process of nitrile transformation into amide and acid; microbial biosensor systems for acrylamide and acrylonitrile determination in water. 2001–2015 - Nonspecific effect of physiologically active and toxic compounds in combination with electromagnetic radiation of low intensity on biological systems and their models. 2007–present - Phytoremediation of salted soil and water polluted by heavy metals. 2013–present - Solid-surface fluorescence of polycyclic aromatic hydrocarbons and heteroaromatic compounds, сhemical sensors. Professional Appointments: 1988–1997 - Junior Research Scientist, Research Scientist in Saratov Branch of All-Russian Institute of Genetics& Selection of Industrial Microorganisms. 1997–2009 - Lecturer of biochemistry in Saratov Military Institute of Biological and Chemical Safety. 2001–2008 - Associate Professor of Ecology Department, Saratov State Technical University.

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2008–2009 - Professor of Ecology Department, Saratov State Technical University. 2009–2016 - Head of Nature & Technosphere Safety Department, Yuri Gagarin Saratov State Technical University. 2016–present - Professor of Nature & Technosphere Safety Department, Yuri Gagarin Saratov State Technical University. Honors: 2013 - Academic title “Professor” Publications from the Last 3 Years: 1. Strashko, A.V., Rogacheva, S.M., Gubina, T.I., Shipovskaya, A.B., and Mel’nikov, A.G. 2016. A sorption-fluorimetric method for the analysis of polycyclic aromatic hydrocarbons in aqueous solutions and a sorbent for the implementation of the method. Patent RF 2,581,411. 2. Pankratov, A.N., Uchaeva, I.M., Rogacheva, S.M., and Volkova, E.V. 2016. “Spatial and electronic structure of the pyrene molecule, tripaflavin cation and eosin anions as a prerequisite for interpreting their solid-phase fluorescence.” Izvestiya of Saratov University. New Series. Series: Chemistry. Biology. Ecology 16:393−8; in Rus. doi:10.18500/1816-9775-2016-16-4-393-398. 3. Shipovskaya, A.B., Malinkina, O.N., Zhuravleva, Yu.u., and Rogacheva, S.M. 2016. “Synthesis of silicon-containing chitosan hydrogels in a glycolic acid medium.” Advances in Materials Science and Engineering. 2016:8. Article ID 3951703, doi.:10.1155/2016/3951703. 4. Rogacheva, S.M., Shipovskaya, A.B., Volkova, E.V., Khurshudyan, G.N., Suska-Malawska, M., and Gubina, T.I. 2018. “Solid-state surface luminescence of polycyclic aromatic hydrocarbons adsorbed on cellulose diacetate matrices.” Proceedings SPIE 10716:20-1–6 Accessed April 26, 2018. doi:10.1117/12.2314855.

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5. Rogacheva, S.M., Volkova, E.V., Otradnova, M.I., Gubina, T.I., and Shipovskaya, A.B. 2018. “Solvent Effect on the Solid-Surface Fluorescence of Pyrene on Cellulose Diacetate Matrices.” International Journal of Optics 2018:6. Article ID 3012081. Accessed June 11, 2018. doi:10.1155/2018/3012081. 6. Rogacheva, S., Gubina, T., Pisarenko, E., Zhutov, A., Shilova, N., and Wiłkomirski, B. 2018. “Phytoextraction of copper and nickel from soils characterized by different degree of chloride salinity”. Journal of Elementology. 23(1):119-35. DOI: 10.5601/jelem. 2017.22.2.1388. 7. Strashko, A.V., Gubina, T.I., Rogacheva, S.M., Shipovskaya, A.B., and Volkova, E.V. 2018. A sorption-fluorimetric method for quantitative analysis of polycyclic aromatic hydrocarbons in aqueous solutions. Patent RF 2,647,475.

Anna B. Shipovskaya Affiliation: Department of Polymers, Saratov State University, Saratov, Russia Education: 1990 - Diploma of Saratov State University named after N.G. Chernyshevsky of higher education on the specialty “Chemistry” with the qualification of “Chemist” 1996 - Diploma of candidate of sciences KT No 023958 of 10.04.1996, specialty 02.00.04 (physical chemistry) 1999 - Certificate of Associate Professor, DC No 015346 of 16.06.1999, the academic title of Associate Professor of the Chair of Polymers 2010 - Diploma of Doctor of Sciences, DDN No 013416 of 24.12.2009, specialty 02.00.04 (physical chemistry) Business Address: 83 Astrakhanskaya St., 410012 Saratov, Russian Federation

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Research and Professional Experience: 1990–2005 - Structure formation and optical activity of cellulose acetates 2006–present - Phase state and optical activity of natural polysaccharide−solvent systems 2012–present - Development of sensor systems on the basis of polysaccharide matrices for the luminescence analysis of polycyclic hydrocarbons and heteroaromatic compounds in liquid media Professional Appointments: 1992–1995 - Saratov State University, Chemistry Faculty, Chair of Technical Chemistry and Catalysis, Senior Lecturer 1995–1997 - Saratov State University, Chemistry Faculty, Chair of Polymers, Senior Lecturer 1997–2010 - Saratov State University, Chemistry Faculty, Chair of Polymers, Associate Professor 2010–2016 - Saratov State University, Institute of Chemistry, Basic Chair of Polymers, Head of Chair 2016–present - Saratov State University, Institute of Chemistry, Chair of Polymers based on ACRYPOL Ltd., Head of Chair 2005–present - Saratov State University, Institute of Chemistry, Deputy Director for Research Honors: 1999 - Academic title “Associate Professor” Publications from the Last 3 Years: 1. Strashko, A.V., Shipovskaya, A.B., Gubina, T.I., Malinkina, O.N., and Melnikov, A.G. 2015. “Usage of cellulose acetate membranes for the sorption-luminescence determination of pyrene in aqueous media.” Petroleum Chemistry 55:292–300. 2. Shipovskaya, A.B., Gubina, T.I., Strashko, A.V., and Malinkina, O.N. 2015. “Cellulose diacetate films as a solid-phase matrix for fluorescence analysis of pyrene traces in aqueous media.” Cellulose 22:P. 1321–32.

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3. Strashko, A.V., Rogacheva, S.M., Gubina, T.I., Shipovskaya, A.B., and Mel’nikov, A.G. 2016. A sorption-fluorimetric method for the analysis of polycyclic aromatic hydrocarbons in aqueous solutions and a sorbent for the implementation of the method. Patent RF 2,581,411. 4. Shipovskaya, A.B., Malinkina, O.N., Zhuravleva, Yu.u., and Rogacheva, S.M. 2016. “Synthesis of silicon-containing chitosan hydrogels in a glycolic acid medium.” Advances in Materials Science and Engineering. 2016:8. Article ID 3951703, doi.:10.1155/2016/3951703. 5. Malinkina, O.N., Sobolev, A.M., and Shipovskaya, A.B. 2016. “Hybrid nanogels based on hydrochloride–ascorbate chitosan derived from a sol-gel biomimetic synthesis” BioNanoScience 6(2):157–61. 6. Shipovskaya, A.B., Fomina, V.I., Kazmicheva, O.F., Rudenko, D.A., and Malinkina, O.N. 2017. “Optical Activity of Films Based on Chitosan of Various Molecular Masses and Modifications.” Polymers Science 59 A:330–41. 7. Lugovitskaya, T.N., and Shipovskaya, A.B. 2017. “Physicochemical properties of aqueous solutions of L-aspartic acid containing chitosan.” Russian Journal of General Chemistry 87:782–7. 8. Zhuravleva, Yu.Yu., Malinkina, O.N., Bratashov, D.N., and Shipovskaya, A.B. 2017. “Formation features and AFM studies of the siliconchitosan-containing glycerohydrogel surface.” IOP Conference Series: Materials Science and Engineering 256: 012011. doi:10.1088/1757-899X/256/1/012011. 9. Rogacheva, S.M., Shipovskaya, A.B., Volkova, E.V., Khurshudyan, G.N., Suska-Malawska, M., and Gubina, T.I. 2018. “Solid-state surface luminescence of polycyclic aromatic hydrocarbons adsorbed on cellulose diacetate matrices.” Proceedings SPIE 10716:20-1–6. Accessed April 26, 2018. doi:10.1117/12.2314855.

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10. Rogacheva, S.M., Volkova, E.V., Otradnova, M.I., Gubina, T.I., and Shipovskaya, A.B. 2018. “Solvent Effect on the Solid-Surface Fluorescence of Pyrene on Cellulose Diacetate Matrices.” International Journal of Optics 2018:6. Article ID 3012081. Accessed June 11, 2018. doi:10.1155/2018/3012081. 11. Strashko, A.V., Gubina, T.I., Rogacheva, S.M., Shipovskaya, A.B., and Volkova, E.V. 2018. A sorption-fluorimetric method for quantitative analysis of polycyclic aromatic hydrocarbons in aqueous solutions. Patent RF 2,647,475. 12. Gegel, N.O., Zhuravleva, Yu.Yu., Shipovskaya, A.B., Malinkina, O.N., and Zudina, I.V. 2018. “Influence of Chitosan Ascorbate Chirality on the Gelation Kinetics and Properties of SiliconChitosan-Containing Glycerohydrogels.” Polymers. 10(3):259. Accessed February 28, 2018. doi:10.3390/polym10030259.

Tamara I. Gubina Affiliation: Nature & Technosphere Safety Department, Yuri Gagarin Saratov State Technical University Education: 1959–1964 - Saratov State University, Chemistry Faculty. 1980 - Candidate of chemical sciences (=Ph.D.) in the specialties “Organic Chemistry”. 2000 - Doctor of chemical sciences in the specialty “Organic Chemistry”. Business Address: 77 Politechnicheskaya St., 410054 Saratov, Russian Federation Research and Professional Experience: 1964–2000 - Chemistry of heterocyclic compounds. 2000–present - Ecotoxocology of new organic compounds; phytoremediation of soil and water polluted by heavy metals; solid-

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surface fluorescence of polycyclic aromatic hydrocarbons and heteroaromatic compounds, сhemical sensors. Professional Appointments: 1964–1997 - Junior Research Scientist, Research Scientist, Senior Research Scientist in Scientific Research Institute of Chemistry of Saratov State University. 1997–1999 - Doctoral Student in Chemistry Faculty, Saratov State University. 1999–2009 - Professor, Head of Ecology Department, Saratov State Technical University. 2009–2014 - Professor of Ecology Department, Saratov State Technical University. 2014–present - Professor of Nature & Technosphere Safety Department, Yuri Gagarin Saratov State Technical University. Honors: 2010 - Academic title “Professor” Publications from the Last 3 Years: 1. Strashko, A.V., Shipovskaya, A.B., Gubina, T.I., Malinkina, O.N., and Melnikov, A.G. 2015. “Usage of cellulose acetate membranes for the sorption-luminescence determination of pyrene in aqueous media.” Petroleum Chemistry 55:292–300. 2. Shipovskaya, A.B., Gubina, T.I., Strashko, A.V., and Malinkina, O.N. 2015. “Cellulose diacetate films as a solid-phase matrix for fluorescence analysis of pyrene traces in aqueous media.” Cellulose 22:P. 1321–32. 3. Strashko, A.V., Rogacheva, S.M., Gubina, T.I., Shipovskaya, A.B., and Mel’nikov, A.G. 2016. A sorption-fluorimetric method for the analysis of polycyclic aromatic hydrocarbons in aqueous solutions and a sorbent for the implementation of the method. Patent RF 2,581,411.

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4. Plotnikova, O.A., Mel’nikov, A.G., Mel’nikov, G.V., Gubina, T.I. 2016. Quenching of tryptophan fluorescence of bovine serum albumin under the effect of ions of heavy metals. Optics and Spectroscopy. 120(1):65–9. 5. Gubina, T.I., Ykhova, A.A., Isaeva, S.V., Tumskiy, R.S., Aniskov, A.A., and Klochkova, I.N. 2017. The determination of biological effects of new heterocyclic compounds on plants and the evaluation of environmental safety of their application. Izvestiya of Saratov University. New Series. Series: Chemistry. Biology. Ecology 17(3):267−73; in Rus. doi: 10.18500/1816-9775-2017-173-267-273. 6. Rogacheva, S.M., Shipovskaya, A.B., Volkova, E.V., Khurshudyan, G.N., Suska-Malawska, M., and Gubina, T.I. 2018. “Solid-state surface luminescence of polycyclic aromatic hydrocarbons adsorbed on cellulose diacetate matrices.” Proceedings SPIE 10716:20-1–6 Accessed April 26, 2018. doi:10.1117/12.2314855. 7. Rogacheva, S.M., Volkova, E.V., Otradnova, M.I., Gubina, T.I., and Shipovskaya, A.B. 2018. “Solvent Effect on the Solid-Surface Fluorescence of Pyrene on Cellulose Diacetate Matrices.” International Journal of Optics 2018:6. Article ID 3012081. Accessed June 11, 2018. doi:10.1155/2018/3012081. 8. Rogacheva, S., Gubina, T., Pisarenko, E., Zhutov, A., Shilova, N., and Wiłkomirski, B. 2018. “Phytoextraction of copper and nickel from soils characterized by different degree of chloride salinity”. Journal of Elementology. 23(1):119-35. DOI: 10.5601/jelem. 2017.22.2.1388. 9. Strashko, A.V., Gubina, T.I., Rogacheva, S.M., Shipovskaya, A.B., and Volkova, E.V. 2018. A sorption-fluorimetric method for quantitative analysis of polycyclic aromatic hydrocarbons in aqueous solutions. Patent RF 2,647,475.

In: Cellulose Acetate Editor: Calvin Roberson

ISBN: 978-1-53614-704-9 © 2019 Nova Science Publishers, Inc.

Chapter 3

PRODUCTION OF CELLULOSE ACETATE FROM AGRICULTURAL RESIDUES Rafael Garcia Candido* Biotechnology Department, Engineering School of Lorena, São Paulo University, Lorena, Brazil

ABSTRACT Cellulose acetate (CA) is one of the most important esters of cellulose due to its renewable source, biodegradability, non-toxicity, low cost, and very poor flammability property. According to a recent report by Global Industry Analysis, the worldwide market of cellulose acetate is projected to about 1.05 million metric tons by 2017 and its estimated price is around $1.80/lb. Amongst the applications of CA are the manufacture of fibers, films, membranes, paints, plastics, cigarette filters, coats, textile, dialyzers, drugs, and biomedical utilities. The most traditional material resources for the industrial acetylation of cellulose are wood and cotton. However, regarding its availability in large amounts as a result of its widespread cultivation on a global scale, agricultural wastes have become an attractive renewable resource for the synthesis of cellulose acetate. Agricultural commodities are the key raw materials *

Corresponding Author Email: [email protected].

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Rafael Garcia Candido available to humanity for the sustainable production of numerous industrial and non-food consumer products, which led to the growing interest in the chemistry of compounds derived from biomass, and to exertions that aim at the use of agricultural wastes as alternative sources of chemicals, energy and materials. A positive feature of the trend in use of agricultural wastes, such as sugarcane bagasse, wheat and rice straw, cereal straws, and corn stove, as a feedstock for value-added products is that they are fairly free from wide price fluctuations, and are not subject to the debates about the use of agricultural food materials, as grains and cereals, for the production of chemicals, polymers, and materials, Furthermore, the concern about growth of CO2 emissions efforts led to the necessity to move toward green material solutions that fit into in the search of a sustainable development policy and low environmental impact resulting in the increase of investigations about the utilization of lignocellulosic materials as alternative sources of chemicals and energy. The major barriers to produce cellulose-based products from agricultural residues are the heterogeneity of the raw material, the experimental conditions reproducibility, the heterogeneous phase of the synthesis reaction, the difficulty of purification, the effluent disposal, and the control of the product quality.

Keywords: cellulose acetate, agricultural residue, green chemistry

INTRODUCTION Due to the great cellulose availability (about 200 million tons per year) (Ünlu, 2013), the manufacture of cellulose derivatives has attracted significant attention recently. In comparison to the polymers synthesized from fossil sources, cellulose derivatives are biodegradable and have a lower environmental impact (Das et al., 2014). Industrially, cellulose acetate (CA) is one of the most important cellulose esters because of its origin from a renewable source, biodegradable, non-toxicity, low cost, and low inflammability (Buchanan et al., 1993; Sun et al., 2013). Global Industry Analysis reported that the worldwide market of cellulose acetate in 2017 was about 1.05 million metric tons, and its estimated price was around $1.80/lb (Cheng et al., 2010). Typically, CA is obtained by a two-step acetylation process (Figure 1) which involves the reaction of the cellulose with acetic acid, a surplus of

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acetic anhydride, and sulfuric acid as the catalyst, followed by a hydrolysis reaction to produce a CA with the desirable degree of substitution (DS), about 2.45–2.5. This DS range grants that CA possesses high solubility (in several types of solvent systems) and good melt properties, facilitating CA’s utilization in a variety of consumer products (Steinmeier, 2004; Cao et al., 2007; Fischer et al., 2008; Puls et al., 2011). This traditional industrial process owns some disadvantages. The cellulose polymer chain can be degraded by the action of H2SO4 in the acetylation stage decreasing the molecular weight of CA (Kuo and Bogan, 1997). In addition, a great amount of water is utilized in the neutralization of the excess of sulfuric acid catalyst (Cao et al., 2007). In order to overcome these problems, other methods have been investigated in synthesize of CA. These methods aim principally the replacement of the sulfuric acid and include the utilization of N,N-carbonyldiimidazole, dialkyl-carbodiimide, iminium chlorides, ring-opening esterification, transesterification and iodine (Heinze et al., 2006; Biswas et al., 2009).

Figure 1. Synthesis of cellulose acetate.

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Cellulose acetate can be applied in textiles, cigarette filters, surface coatings and inks as an additive, and photographic negatives, celluloid, microfilm, microfiche and audio tape as a carrier (Gedon and Fengl, 1993; Cheng et al., 2010;). However, the main use of cellulose acetate as a raw material is in the manufacture of membranes. Moderate flux, high salt rejection properties, cost-effectiveness, relatively easy production, and non-toxicity are the main advantages in the use of CA as membrane materials (Kamal et al., 2014). Cellulose acetate membranes have been used widely, for instance, in water desalination, in hemodialysis process, and in controlled drug release (Haddad et al., 2004; Liao et al., 2005; Wang et al., 2012). The most common raw materials for the industrial acetylation of cellulose are wood and cotton. Nevertheless, agricultural wastes are nowadays an attractive renewable resource for the synthesis of cellulose acetate considering their availability in large amounts as a result of their globally widespread cultivation (Fan et al., 2014). Agricultural commodities are the key sources for the world’s sustainable development, leading to the growing interest in the chemistry of compounds derived from biomass, and to exertions that aim at the utilization of agricultural wastes as alternative raw materials of chemicals, energy, and materials. A positive feature of the trend in use of agricultural wastes as a feedstock for value-added products is that they are free from wide price fluctuations, and are not subject to the debates about the use of agricultural food materials, as grains and cereals, for the production of non-food products (Shaikh et al., 2009; Heguaburu et al., 2012).

1. USE OF AGRICULTURAL RESIDUES IN THE GREEN CHEMISTRY AND SUSTAINABILITY CONCEPTS More and more, sustainable development is turning into a priority for businesses and governments alike. We frequently hear about the damages caused by the global warming and the depletion of fossil reserves, and it

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seems to be just a matter of time before we are forced to look at renewable resources to fulfill our needs in a sustainable fashion. Therefore, sustainability, industrial ecology, eco-efficiency, and green chemistry are guiding the development of the next generation of materials, chemicals, and processes (Khalil et al., 2012). Green chemistry is concerned with the efficient utilization of (preferably renewable) resources together with the elimination of waste and non-use of toxic and/or hazardous reagent sand solvents in the obtainment and application of chemical products (Anastas and Warner, 1998; Sheldon et al., 2017). Sustainability is comprised of three components: societal, ecological and economic, otherwise referred to as the three Ps, people, planet, and profit. Consequently, in opposite to green chemistry, sustainability consists of an economic component (Sheldon, 2016). In order for a technology to be considered sustainable the following conditions have to be fulfilled (Figure 2): (i) natural resources should be utilized at rates that do not unacceptably deplete supplies over the long term and (ii) residues should be generated at rates no higher than can be assimilated readily by the natural environment (Graedel, 2016). The future production of chemicals that are verifiably green and sustainable “from cradle to grave” is a vital part of a sustainable society that can maintain its population with a reasonable standard of living without irreversibly disturbing natural systems (Sanders et al., 2012). Nowadays, the emphasis is on the replacement of non-renewable fossil resources (crude oil, coal, and natural gas) by renewable biomass, principally the agricultural residues, as a sustainable feedstock for the production of commodity chemicals and liquid fuels (Yang et al., 2013). It is estimated that 3.7 x 109t of agricultural residues is produced annually as by-products by agricultural industries worldwide and that in 2050 a significant part of the required fuels for transportation and electricity generation will be produced from biomass (Sanders et al., 2012; Bentsen et al., 2014). A change to renewable biomass as a feedstock will provide an environmentally beneficial reduction in the carbon footprint of chemicals and liquid fuels. An additional benefit can come from the substitution of existing products by inherently safer alternatives with reduced environmental footprints (De Jong et al., 2012). Furthermore, the

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utilization of agricultural residues can contribute to the development of the waste-based economy. The following main strategies have to be followed to apply all these biomass sources for the bulk chemical industry (Figure 3): 1) Acceptance of their heterogeneity and convert as much as possible of the components into small molecules, which can be used in the chemical industry. 2) Development of specific reactions to convert single components into valuable building blocks that can be recovered from the complex mixture at low cost and energy inputs. 3) First separate the biomass components into ‘homogeneous’ components (protein, fats, starch, cellulose, hemicellulose, lignin, and minerals) and then transform each of these into ‘pure’ building blocks that can be separated from the solution (Sanders et al., 2012).

Figure 2. Concept of sustainable product.

Figure 3. Essential requirements for an ideal process for use of biomass.

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2. SYNTHESIS OF CELLULOSE ACETATE FROM AGRICULTURAL RESIDUES 2.1. Sugarcane Sugarcane is a perennial grass originating from Asia and is the most harvested crop in the world. As consequence, its residual bagasse (the solid and fibrous fraction which remains from usual milling of sugarcane) is the most abundant agricultural waste in the world achieving an annual production of 54 million dry tons (Rodrigues et al., 2010; Bizzo et al., 2014; Santos, Ely et al., 2016). The recent advances on biotechnology and the development of the biorefinery concept expanded the possibilities of bagasse application, which also contributes to the greenhouse gas emission reduction, to the improvement of food security and to a lower environmental impact (Cheribini, 2010; Khuong et al., 2014). It is estimated that for each ton of sugarcane processed, 140 kg of sugarcane straw is generated. Generally, the straw either is burned to allow the manual harvest of sugarcane or remains in the field after mechanical harvest to assist in soil treatment (Silva et al., 2010). Indeed, the traditional practice of burning is being ceased progressively, leaving only the mechanized harvest and leading to a higher generation of sugarcane straw which can be utilized as energy and chemical product feedstock. Shaikh et al., (2009) produced CA from sugarcane bagasse and pointed out that as the reaction time increased, the DS was found to be steady in the range of 2.8–2.9 and the intrinsic viscosities are seen to decrease due to chain degradation under the acidic conditions. Consequently, the molecular weight distribution (MWD) also decreased with acetylation reaction time wherein the samples reacted for more than 8 h showed the lowest the MWD. This means that after 8 h of reaction the remaining hemicellulose is almost completely removed during the workup. In the thermal analysis, it was observed that the thermal stability of CA increases with acetylation reaction time and reaches a maximum at 8 h reaction time. According to the authors, the thermal stability also depends on molecular weight and

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crystallinity of the polymer. Generally, lower the molecular weight or lower the crystallinity, the easier the degradation of the polymer. Sun et al., (2004) verified that the use of the catalyst N-bromosuccinimide (NBS) substantially accelerated the rate of reaction in comparison with the reaction without NBS. Use of 1% NBS (1.0 g NBS in 100 ml acetic anhydride) as a catalyst resulted in an increase in the weight percent gain (WPG) by 19.6%, which was approximately four times higher than the WPG obtained at the same condition without a catalyst. The WPG also increased with the increment of reaction temperature and time. The increment of the temperature increased the WPG by 24.7%. The reason for this significant increase of acetylation by raising temperature was probably due to the favorable effect of temperature on the compatibility of the reaction ingredients and swellability of the bagasse (Khalil et al., 1995). During the acetylation process, the fiber swells as the reaction proceeds, requiring rupture of the hydrogen bonding network. Usually, increasing temperature favored disrupting such hydrogen bonds, swelling the fibers, diffusing the esterifying agent, and moving the reactant molecules, thus raising the reaction rate. The increment of the reaction time increased the WPG in 2%. This increment of acetylation by prolonging the duration of the reaction was a direct consequence of the favorable effect of time on diffusion and adsorption of the reactants between the acetic anhydride and the cellulose. CA was tested as sorbent of oils. The results of the tests showed that CA from sugarcane bagasse can be used as potential sorbents to substitute nonbiodegradable synthetic materials in oil spill cleanup. It could be used effectively to recover oil spilled in bodies of refining or heavy industrial wastewater, and the water such as in lakes, rivers, and oceans. More importantly, it was found that CA sorbent can be recycled 10 times for oil spill cleanup by a simple squeezing operation evincing its economic potential. The synthesized cellulose acetate from sugarcane bagasse by Candido et al., (2017) presented a DS of 2.52 and 43.50% of acetyl groups characterizing it as a triacetate. The high lignin solubilization during the

Production of Cellulose Acetate from Agricultural Residues

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cellulose extraction process was extremely important in order to achieve a high DS. Lignin competes with cellulose for the acetylation reactants and, consequently, a great amount of lignin could decrease the yield of the acetylation process. The authors stated that this DS value was obtained also because of cellulose possessed low viscosity. The higher accessibility to the cellulose chain, as consequence of the low viscosity, increased the efficiency of the activation stage in the acetylation process. There was a higher access of the acetic anhydride to the free OH groups of cellulose, improving the activation of cellulose for the acetylation process second stage. The activation stage is crucial to the synthesis of cellulose acetate with DS ≥ 2.0. In the thermal analysis was observed an endothermic peak at 32◦C, which represents the glass transition (Tg) of the CA. This Tg value for the CA synthesized from sugarcane bagasse is practically the same as the value reported to a CA commercial sample (Tg = 33◦C) (Candido, 2015). Taking account that the commercial grade CA is 100% pure, it can be concluded that the presence of lignin and hemicellulose in the composition of sugarcane bagasse CA did not alter this thermal property. Sugarcane straw cellulose (SSC) was the raw material of the acetylation reaction carried out by Candido and Gonçalves (2016). The cellulose triacetate obtained presented a DS value of 2.72 ± 0.19 and a percentage of acetyl groups of 41.05 ± 2.77%. The proceeding to extract cellulose contributed to the almost total acetylation of SSC. During the process, the reactants, principally the NaOH, promote the swelling of the fibers, which increases the accessibility of acetic anhydride to the OH groups of cellulose and improves the activation of cellulose pulp for the acetylation reaction. The cellulose activation stage owns an important role. It is almost impossible to synthesize soluble CA (DS ≥ 2.0) without the activation stage. In this process, the reactant diffuses into the inner layer of the cellulose fiber, disrupts both intra and intermolecular hydrogen bonds, and degrades the crystalline region of the fiber, raising the accessibility to the OH groups which results in the increment of the DS value.

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Rafael Garcia Candido

2.2. Cotton The main residues of cotton culture are the cotton burr and the cottonseed hull. Cotton burr, a component of picker trash, is a byproduct of cotton production which may be applied as fuel for boilers or occasionally as mulch. Cottonseed hull is a low-value product of cottonseed oil extraction used as roughage in animal feed, as mulch, and as a substrate for mushroom production. Both materials are readily available and quite cheap (Cheng et al., 2010). The waste cotton fabrics (WCF) are wastes from used clothes and leftover materials of cotton textile industry (Tian et al., 2014). They are usually landfilled or incinerated, but this procedure not only generates environmental pollution but also takes into a great waste of these valuable resources (Miranda et al., 2007). It was already demonstrated that it is possible to recycle them into value-added products (Sun et al., 2013; Sun et al., 2014). Cao et al., (2016) studied the acetylation of WCF using an ionic liquid (IL) as catalyst aiming the production of water-soluble CA and observed that the DS values could be easily regulated by varying the amount of IL catalyst and the time of acetylation. No water-soluble CA was obtained without IL catalyst because most of the cellulose was not reacted. On the other hand, the synthesis of water-soluble CA increased significantly with the increase of ILs amount. However, in a high concentration of IL, the higher time reaction (>2h) the lower water-solubility. This situation can be ascribed to the increase of DS values in high reaction times leading to the decrease of solubility in water. Prolonging the reaction time has a favorable effect on the diffusion and absorption of reactants culminating in higher DS values. Under low amount of IL (