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Polymer Chemistry CLOTHWORKERS LIBRARY UNIVERSITY OF LEEDS THERMAL AND OXIDATIVE DEGRADATION OF AN AROMATIC POLYAMIDE. by «. Shojan Nanoobhai Patel 2. Submitted in accordance with the requirement for the degree of Doctor of Philosophy under the supervision of Professor I.E. McIntyre and Dr. S.A. Sills. The candidate confirms that the work submitted is his own and that appropriate credit has been given where reference has been made to work of others. Department of Textile Industries, The University of Leeds, Leeds, LS2 9JT. December 1992. CLASS MARK T:; ~S 2tC\4 -1- ABSTRACT. The thermal oxidation of an aromatic polyamide fibre, namel\' poly(m-xylylene adipamide) has been investigated. The volatile and non-volatile products of oxidation identified using T.L.C., H.P.L.C. and G.C.-M.S. include homologous series of monocarboxylic acids, dicarboxylic acids, n-alkyl amines, diamines and aldehydes. Furthermore, several aromatics, ketones and amides were also identified. Mechanisms for their derivation have been proposed which are based on oxidation reactions already established in polymer chemistry. These include a mechanism of ~ scission by an alkoxy radical thought to be responsible for the creation of the homologous series. MXD,6 fibres were also spun incorporating 100, 200 and 400ppm of a cobalt catalyst and the effect of the metal ions on the oxygen uptake of the fibres was investigated. The results show a consistent increase in the rate of oxygen uptake as the concentration of the cobalt is increased. Furthermore, T.G.A. oxidative degradation studies, conducted at isothermal temperatures in the solid state, show decreases in the activation energies associated with fibre oxidation with increased cobalt concentrations, implying the cobalt is a catalyst for oxidation. A mechanism for the behaviour of the catalyst in the fibre has been proposed and it is thought the cobalt works predominantly as a catalyst for the initiation of radicals whilst in the melt stage of polymer spinning, then to a lesser extent as a catalyst for radical propagation whilst in the solid phase. -11- CONTENTS. PAGE. Abstract. 1 Contents. 11 List of Figures. VI List of Schemes. IX List of Tables. Xl List of Abbreviations and Symbols. Xlll Acknowledgements. XlV CHAPTER ONE :- INTRODUCTION. 1.1 HISTORY OF POLYAMIDES. 2 1.2 TERMINOLOGY AND NOMENCLATURE. 5 1.3 PREPARATIVE METHODS FOR POLYAMIDES. 7 1.3.1 Melt Polycondensation. 7 1.3.2 Ring Opening Polymerization. 8 1.3.3 Low Temperature Polycondensation. 10 1.4 AROMATIC POLYAMIDES. 11 1.4.1 Amorphous Glass-Clear Aromatic Polyamides. 11 1.4.2 Crystalline Wholly Aromatic Polyamides. 14 1.4.3 Crystalline Aliphatic-Aromatic Polyamides. 16 1.5 THE RISE AND FALL OF MXD,6. 20 1.5.1 MXD,6 Preparation. 20 1.5.2 Intermediates for MXD,6. 21 1.5.2.1 Adipic Acid. 21 1.5.2.2 Metaxylylene diamine. 22 1.5.3 MXD,6...The Failed Fibre. 24 1.5.4 MXD,6 Today. 29 -111- PAGE. CHAPTER TWO :- POLYMER DEGRADATION. 2.1 INTRODUCTION. 32 2.2 THERMAL DEGRADATION OF POLYAMIDES. 34 2.2.1 Introduction. 34 2.2.2 Mechanisms in Polyamide Thermal Degradation. 35 2.3 OXIDATIVE DEGRADATION OF POLYAMIDES. 45 2.3.1 Introduction. 45 2.3.2 Mechanisms in Polyamide Oxidation. 45 2.4 PHOTODEGRADATION OF POLYAMIDES. 52 2.4.1 Introduction. 52 2.4.1.1 Yellowing. 53 2.4.2 Mechanisms in Photo-oxidation. 55 2.4.2.1 Impurity Chromophores. 56 2.4.2.2 Polymer Constitution. 61 2.4.3 Photo-oxidation of Polyamides. 62 2.5 THE THERMAL DEGRADATION OF MXD,6. 68 2.6 OBJECTIVE OF STUDY. 71 CHAPTER THREE :- EXPERIMENTAL. 3.1 MATERIALS. 73 3.2 POLYMERIZATION TECHNIQUES. 77 3.2.1 Two Stage Polycondensation. 77 3.2.1.1 Salt Formation. 77 3.2.1.2 Polymerization. 77 3.2.2 One Stage Direct Polycondensation. 78 3.3 FIBRE SPINNING. 80 3.4 CHARACTERIZATION. 82 3.4.1 Chromatographic Techniques. 82 3.4.1.1 Thin Layer Chromatography. 82 3.4.1.2 High Performance Liquid Chromatography. 89 3.4.1.3 Gas Chromatography - Mass Spectroscopy. 94 -rv- PAGE. 3.4.2 Molecular Weight Measurement Techniques. 94 3.4.2.1 End Group Analysis. 94 3.4.2.1.1 Amine End Groups Analysis. 94 3.4.2.1.2 Carboxyl End Groups Analysis. 96 3.4.2.2 Dilute Solution Viscometry. 98 3.4.3 Spectroscopic Techniques. 100 3.4.3.1 Fourier Transform Infrared Spectroscopy. 100 3.4.4 Thermal Analysis Techniques. 100 3.4.4.1 Differential Scanning Calorimetry. 100 3.4.4.2 Thermogravimetric Analysis. 100 3.5 OXYGEN PERMEATION MEASUREMENTS. 101 3.5.1 Introduction. 101 3.5.2 Method. 101 3.6 DEGRADATION. 102 3.6.1 Non-volatile Analysis. 102 3.6.1.1 Analysis According to East et al. 102 3.6.1.2 Analysis according toMori et al. 105 3.6.2 Volatile Analysis. 106 3.6.3 Melt Phase Thermal Degradation. 107 3.7 SYNTHESIS OF EXPECTED DEGRADATION PRODUCTS. 108 3.7.1 Isophthalamic Acid. 108 3.7.2 Adipamic Acid. 109 CHAPTER FOUR :- RESULTS AND .DISCUSSION.. 4.1 MXD,6 POLYMERIZATION. 111 4.2 OXIDATION OF SPUN FIBRE. 114 4.2.1 Oxygen Uptake Experiments. 114 4.2.2 Thermogravimetric Analysis of MXD,6 Fibres with 119 and without Cobalt. -v- PAGE. 4.3 MXD,6 FIBRE DEGRADATION STUDIES. 128 4.3.1 Non-volatile Acid Hydrolysis Studies. 128 4.3.1.1 Degradation Product Characterization via Steam Distillation. 128 4.3.1.1.1 Analysis of Carboxylic Acid Salts. 130 4.3.1.1.2 Analysis of Amines. 133 4.3.1.1.3 Analysis of Free Carboxylic Acids in Solution. 133 4.3.1.1.3.1 Aliphatic Carboxylic Acids. 133 4.3.1.1.3.2 Aromatic Carboxylic Acids. 136 4.3.1.2 Evaporation Technique. 143 4.3.2 Volatile Headspace Analysis. 143 4.3.2.1 Headspace Analysis of Amines. 145 4.3.2.2 Headspace Analysis of Aldehydes and Ketones. 147 4.3.2.3 Headspace Analysis using G.C.-M.S. 150 4.3.3 Analysis of Polymer Residue after Degradation. 152 4.3.3.1 Analysis of Degraded MXD,6 by Intrinsic Viscosity. 153 4.3.3.2 Analysis of Degraded MXD,6 by End Group Analysis. 156 4.4 INFLUENCE OF COBALT IONS ON THE OXIDATION OF 157 MXD,6. 4.4.1 The Role of Cobalt Ions in the Initiation Reactions. 158 4.4.2 The Role of Cobalt Ions in the Propagation Reactions. 162 4.5 DISCUSSION. 163 4.5.1 Radicals formed from the Fission of the CH2-NH and CH2-CO 165 Bonds and their consequent Reactions. 4.5.1.1 Polyamide Initiation. 165 4.5.1.2 Polyamide Propagation. 166 4.5.1.3 Polyamide Termination. 167 4.5.2 Mechanisms of MXD,6 Oxidation. 169 4.5.2.1 Aliphatic Monocarboxylic Acids. 170 4.5.2.2 Aliphatic Dicarboxylic Acids. 172 4.5.2.3 Aliphatic Mono- and Diamines. 175 4.5.2.4 Aldehydes and Ketones. 177 4.5.2.5 Aromatic Degradation Products. 179 CHAPTER FIVE :- CONCLUSION. 5.1 CONCLUSION AND GENERAL SUMMARY. 183 5.2 RECOMMENDATION FOR FUTURE STUDY. 185 REFERENCES. 186 -Vl- LIST OF FIGURES. PAGE. Chapter One. Figure Number. 1.1 The Isomeric Bisaminomethylnorbornanes. 12 1.2 Grilamid TR55. 13 1.3 Melting Points ofHexamethylene- and m-Xylylene Diamine 24 Polyamide Resins. 1.4 Comparison of the Modulus-Temperature Characteristics ofNylon 26 MXD,6, Nylon 6,6 and Polyester 20T Fibres (dry). 1.5 Comparison of the Modulus-Temperature Characteristics of Nylon 26 MXD,6, Nylon 6,6 and Polyester 20T Fibres (wet). 1.6 Effect of Boil-off on the Stress-Strain Characteristics of Nylon MXD,6. 27 1.7 Effect of Annealing at Constant Length on Shrinkage Behaviour of MXD,6. 28 Chapter Two. 2.1 Amide Bond Fission According to Goodman. 34 2.2 Amide Bond Fission According to Kameerbeek et al and Mortimer. 34 2.3 Cyclic Monomer of Nylon 6,6 Formed During Polymerization. 42 2.4 Mechanism for the Thermo-oxidative and Photo-oxidative Degradation of 46 Polymers. 2.5 Schematic Diagram showing how the Concentration of Peroxide 47 and Apparent Degradation Varies with Increased Oxidation. 2.6 Effect ofWavelength on the Photodegradation of Nylon 6,6. 62 2.7 Regeneration ofFluorescence of Nylon 6.6 66 2.8 'Aldol' Condensation Products of Cyclopentanone Identified by Allen. 67 2.9 Main Fragment ions by Electron Impact for MXD,6. 70 Chapter Three. 3.1 Polymerization Apparatus Utilized in MXD,6 Polymerization. 79 3.2 Relationship between the Log Retention Volume and the Carbon Number 90 for a Series ofMonocarboxylic Acids. 3.3 Oxygen Uptake Apparatus. 101 3.4 Fractionation of Hydrolysate. 104 -vu- PAGE. Chapter Four. 4.1 Fibre Diameters Determined from Optical Microscopic Photographs. 115 4.2 Curves relating the rate of Oxygen Uptake to the Concentration of Cobalt 116 in a Blend of 96% Polyester and 4% MXD,6 at 100°C. 4.3 Curves relating the rate ofOxygen Uptake to the Concentration of 118 Cobalt in MXD,6 at 100°C. 4.4 T.G.A. traces obtained from the Isothermal Heating of MXD,6 at 121 200,210 and 220°C in Air. 4.5 T.G.A. traces obtained from the Isothermal Heating of MXD,6 with 122 100ppm Cobalt at 200, 210 and 220°C in Air. 4.6 T.G.A. traces obtained from the Isothermal Heating of MXD,6 with 123 200ppm Cobalt at 200, 210 and 220°C in Air.
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