Structure-Property Relationships Of Castor Oil-Based Polyurethane Foams

ABSTRACT

Mechanically extracted castor oil (CO) from the seeds of Nigerian wild castor plant (Ricinus communis Linn) was used after purification and chemical modification by PCl5-chlorination and by lead (II) oxide (PbO)-catalysed glycerolysis. FTIR and GC-MS techniques were used for the structural characterisation of the neat and modified polyols, while titrimetric methods were used to determine their physico-chemical characteristics. Using two different formulations of isocyanate/polyol (NCO/OH) ratios of 1/2 and 1/1, rigid, semi-rigid and flexible CO-based polyurethane foams (COPUFs) were prepared by one-shot method. Foam reaction involved either neat CO or its modified polyols containing varying concentrations (10-60 wt%) of the modifier, and 80:20 mixture of 2,4- and 2,6-toluene diisocyanate (TDI) at room temperature (30-350C). Foam reaction took place in presence of stannous octoate and dimethylaminoethanol (DMAE) catalysts, methylene chloride (physical blowing agent) and silicone oil (surfactant). In addition to the basic foam formulation, CaCO3-filler (2-20 wt%) was incorporated in selected sample preparations. Heptachlorotetradecane (HCTD) and heptachloroheptadecane (HCHD), two medium (straight)-chain chlorinated paraffins, were also incorporated in selected preparations as plasticisers and flame retardants (FRs) either singly or as blends of different weight ratios. All foams obtained were characterised in terms of their process parameters such as cream time, free-rise time, gel time, tack-free time and foam rise (ASTM D7487) as well as their physico-mechanical properties namely: density (ASTM D1622-08), water absorption (ASTM D570-98/D2842-12), compressive strength (ASTM D1621-10) and creep recovery (ASTM D2990-09). The structure-property relationships of COPUFs were established through process; physico-chemical, mechanical, morphology and flammability parameters. Glycerol-modified foams (GMFs) were found to be rigid and
viii
moisture resistant, with their densities varying from 24.50-50.50 kg/m3; water absorption (0.73-2.20 wt%); compressive strength (89.20-450.20 KN/m2) and creep recovery (18.5-28.5%). Rigidity in the structure of GMFs increased with modifier concentration and at higher NCO/OH ratios. GMF rigidity was attributed to network formation likely resulting from allophanate and urea crosslinking reactions during foam synthesis. CaCO3-filled foams (CFFs) have shown improvement in moisture resistance, density and compressive strength, but reduction in creep recovery compared to the control (neat) COPUF, with further property enhancements as filler loading was increased from 2-20 wt%. HCTD/HCHD plasticised COPUFs were found to be soft, flexible foams, especially at the lower NCO/OH ratio of 1/2, and at 50:50 (HCTD: HCHD) weight ratios. Foams were also characterised in terms of their flammability properties. Flame properties studied were ignition time (IT), flame propagation rate (FPR) and after-glow time (AGT). Results indicate that IT is closely related to the density of COPUF matrix. Additives (other than plasticisers) generally improved the density, compressive strength or fire retardancy characteristics of the COPUFs. FR treatment of COPUFs has revealed HCTD as a more effective individual FR than HCHD. This is explained in part in terms of greater absorbability (higher add-on) of HCTD in the COPUF system, and also in terms of a vapour phase radical quenching mechanism of action by which the shorter chain and more thermally unstable HCTD released more chlorine radicals per mole than HCHD, thus giving the former early and greater arrestive power of COPUF combustion processes. Microstructural imaging of foams using scanning electron microscopy (SEM) has revealed wide variation in pore size (0.10-0.35 mm) and shape (spherical, oblong and polyhedral), while wall thicknesses ranged from 18-50 μm.

 

 

TABLE OF CONTENTS

Title – – – – – – – – – – i
Declaration – – – – – – – – – ii
Certification – – – – – – – – – iii
Dedication – – – – – – – – – iv
Acknowledgements – – – – – – – – – v
Abstract – – – – – – – – – – vii
Table of Contents – – – – – – – – ix
List of Tables – – – – – – – – – xix
List of Figures – – – – – – – – xxii
List of Plates – – – – – – – – – xxvii
List of Appendices – – – – – – – – – xxix
List of Abbreviations – – – – – – – – – xxxi
CHAPTER ONE: INTRODUCTION
1.1 Preamble – – – – – – – – 1
1.2 Polymers Based on Vegetable Oils – – – – – 3
1.3 Castor Oil – – – – – – – – – 6
1.4 Glycerolysis of Castor Oil – – – – – – 10
x
1.5 Polyurethanes – – – – – – – – 10
1.6 Chemistry of Polyurethane Synthesis – – – – – 11 1.7 Polyurethane Foams (PUFs) – – – – – – 13
1.7.1 Cell Structure – – – – – – – – 15
1.8 Castor Oil-Based Polyurethane Foams (COPUFs) – – – 15
1.9 Polymer Foam Formulations – – – – – – 17
1.10 Structure-Property Relationship in Polymers – – – – 21
1.11 Effect of Filler Incorporation on Morphology and Structure of PUFs – 22
1.12 Flammability Characteristics of PUFs – – – – – 24
1.13 Mechanical Properties of Polymer Foams – – – – 26
1.14 Polymer Foam Geometry – – – – – – 26
1.15 Research Objectives of the Study – – – – – – 27
1.16 Statement of Research Problem – – – – – 28
1.17 Justification/Significance of the Study – – – – – 29
1.18 Contributions to Knowledge – – – – – – – 30
1.19 Scope/Limitations of the Study – – – – – – 30
CHAPTER TWO: LITERATURE REVIEW
2.1 Chemical Modification of Vegetable Oils for PUF Synthesis – – 32
2.2 Polyurethane Additives – – – – – – – 37
xi
2.2.1 Chain Extenders – – – – – – – 38
2.2.2 Fillers – – – – – – – – – 39
2.2.3 Flame Retardants (FRs) – – – – – – – 42
2.2.3.1 Mechanisms of Flame Retardant Action – – – – 43
2.2.4 Plasticisers – – – – – – – – 45
2.2.4.1 Classification of Plasticisers – – – – – – 46
2.2.4.2 Mechanisms of Plasticisation – – – – – – 47
2.3 Characterisation of PUF Properties – – – – – 50
2.3.1 Physico-chemical Properties – – – – – – 50
2.3.1.1 FTIR – – – – – – – – – 51
2.3.2 Mechanical Properties – – – – – – – 52
2.3.2.1 Basic Mechanical Properties of Polymers – – – – 52
2.3.2.1(a) Test Methods – – – – – – – 52
2.3.2.1(b) Tensile Strength (ASTM D 638) – – – – – 53
2.3.2.1(c) Stress-Strain Properties in Tension – – – – 53
2.3.2.1(d) Elastic Modulus – – – – – – – 54
2.3.2.1(e) Flexural Properties of Plastics – – – – – 54
2.3.2.1(f) Hardness (ASTM D 785) – – – – – – 54
2.3.2.1(g) Compressive Strength (ASTM D 695) – – – – 56
xii
2.3.2.2 Mechanical Properties of Solid PUFs – – – – – 55
2.3.2.2(a) Nature of Cell Structure and Orientation – – – – 56
2.3.2.2(b) Compression – – – – – – – 57
2.3.2.2(c) Tension – – – – – – – – 58
2.3.2.3 Factors Influencing Mechanical Properties of Solid Foams – – 58
2.3.3 Morphological Properties – – – – – – 60
2.4 Structure-Property Relationships in PUFs – – – – 63
CHAPTER THREE: MATERIALS AND METHODS
3.1 Materials – – – – – – – – – – 66
3.2 Equipment/machines Used – – – – – – 67 3.3 Methods – – – – – – – – – 67
3.3.1 Seed Collection and Preparation – – – – – 67
3.3.2 Determination of Moisture Content of Seeds – – – – 67
3.3.3 Extraction and Purification of Oil from Castor Bean – – 68
3.3.4 Characterisation of Oil from Castor Bean – – – – 68
3.3.4(a) Physical Analyses – – – – – – – 68
3.3.4(a)(i) pH Measurement – – – – – – – 68
3.3.4(a)(ii) Determination of Refractive Index (RI) – – – 69
xiii
3.3.4(a)(iii) Determination of Specific Gravity (SG) – – – – 69 3.3.4(a)(iv) Determination of Relative Viscosity (RV) – – – 69
3.3.4(b) Chemical Analyses – – – – – – – 70
3.3.4(b)(i) Determination of Acid Number (AN) – – – – 70
3.3.4(b)(ii) Determinationn of Hydroxyl Number (HN) – – – 70
3.3.4(b)(iii) Determination of Saponification Number (SN) – – – 71
3.3.4(b)(iv) Determination of Peroxide Number (PN) – – – 72
3.3.4(b)(v) Determination of Iodine Number (IN) – – – – 72
3.3.4(c) FITR Spectroscopic Analysis – – – – – 73
3.3.4(d) GC-MS Analysis – – – – – – – 73
3.3.4(d)(i) Fatty Acid Profile – – – – – – – 73
3.3.5 Chemical Modification of Castor Oil – – – – – 74
3.3.5(a) Sulphation – – – – – – – – 74
3.3.5(b) PCl5 Chlorination (by Substitution) – – – – – 75
3.3.5(c) Alcoholysis (Glycerolysis) of Castor Oil- – – – 75
3.3.6 Foam-making Procedure – – – – – – 76
3.3.7 Foam Testing – – – – – – – – 77
3.3.7(a) Visual Observation – – – – – – – 77
3.3.7(b) Density Determination – – – – – – 77
xiv
3.3.7(c) Water Absorption – – – – – – – 78
3.3.7(d) Determination of Mechanical Properties – – – – 78
3.3.7(d)(i) Compressive Strength – – – – – – 78
3.3.7(d)(ii) Creep Recovery – – – – – – 79
3.3.8 Flammability Studies – – – – – – 80
3.3.8(a) Flame Retardant (FR) Treatment – – – – – 80
3.3.8(b) Ignition Time (seconds) – – – – – – 80
3.3.8(c) Flame Propagation Rate (cm/s) – – – – – 81
3.3.8(d) After-glow Time (seconds) – – – – – – 81
3.3.8(e) Add-on (%) – – – – – – – – 81
3.3.9 Scanning Electron Microscopic (SEM) Analysis – – – 81
CHAPTER FOUR: RESULTS
4.1 Physico-chemical Properties of Castor Oil (CO) and Modified Castor Oil
Polyols (MCOPs) – – – – – – – – 83
4.1.1 Fatty Acid Composition of the Castor Oil – – – – 84
4.1.2 Physico-chemical Properties of the MCOPs – – – – 85
4.1.2 (a) Variation of Hydroxyl Number and Relative Viscosity in MCOPs – 87
4.1.2(b) Variation of Iodine Number in MCOPs – – – – 88
4.1.2(c) Variation of Hydroxyl Number with Reaction Time during Polyol
xv
Synthesis – – – – – – – – 89
4.1.2(d) Results of FTIR and GC-MS Analysis of the MCOPs – – 90
4.1.2(d)(i) FTIR Spectra – – – – – – – 90
4.1.2(d)(ii) GC-MS Chromatograms – – – – – 95
4.2 Physical Properties of COPUFs- – – – – – 97
4.2.1 Density and Water Absorption of COPUFs – – – – 99
4.2.2 Effect of Filler Incorporation on the Physico-Chemical Properties of COPUFs 100
4.2.3 Comparison of Water Absorption of GMFs, PMFs and CFFs of
20wt% concentration of different NCO/OH ration – – – – 102
4.2.4 Effect of Plasticisation on the Physical Properties of COPUFs – – 103
4.3 Mechanical Properties of COPUFs – – – – – 104
4.3.1 Compressive Strength – – – – – – – 104
4.3.1(a) Effect of Plasticisation on the Compressive Strength of COPUFs 105
4.3.2 Creep Recovery – – – – – – – – 106
4.3.3 Effect of Density on Mechanical Properties of COPUFs – – 108
4.4 Comparison of Physico-mechamical Properties of COPUFs with Standard
Values for the Conventional PUF – – – – – 111
4.5 Flame Properties of COPUFs – – – – – – 111
4.5.1 Effect of Foam Density/Modifier Concentration on Flame Properties
of GMFs – – – – – – – – 112
xvi
4.5.2 Effect of FR Concentration on Flame Properties of COPUFs – – 115
4.5.3 Effect of HCTD/HCHD Blending on Flame Properties of COPUFs 117
4.5.4 Effect of Filler Loading on Flmae Properties of COPUFs – – 118
4.6 Morphological Characteristics of COPUFs – – – – 119
4.6.1 Effect of Modifier Concentration on the Morphology of GMFs – 120
4.6.2 Effect of Filler Concentration on the Morphology of CFFs – – 121
4.6.3 Effect of HCTD/HCHD Plasticisation on the Morphology of COPUFs 123
4.6.4 COPUF Pore Dimensions – – – – – – 123
CHAPTER FIVE: DISCUSSION
5.1 Physico-chemical properties of Castor Seed Oil – – – – 124
5.1.1 Physico-chemical Parameters – – – – – – 124
5.1.2 Results of FITR Analysis – – – – – – – 125
5.1.3 Results GC-MS Analysis – – – – – – 126
5.1.3 (a) Fatty Acid (FA) Composition – – – – – 126
5.2 Physico-chemical Properties of MCOPs – – – – – 127
5.2.1 Variation of Hydroxyl Number (HN) and Relative Visccosity (RV)
in MCOPs- – – – – – – – – 128
5.2.2 Variation of Iodine Number (IN) in MCOPs- – – – – 129
5.2.3 Variation of Hydroxyl Number with Reaction Time during Polyol
xvii
Synthesis – – – – – – – – – 130
5.2.4 Results of FTIR and GC-MS Analyses for the MCOPs – – 131
5.2.4 (a) GMCOPs – – – – – – – – 131
5.2.4 (b) PMCOPs – – – – – – – – 132
5.2.4 (b) (i) FTIR – – – – – – – – 132
5.2.4 (b) (ii) GC-MS – – – – – – – – 133
5.2.4 (c ) Sulphated Castor Oil (SLCO) – – – – – 134
5.3 Physical Properties of COPUFs – – – – – – 134
5.3.1 Process Parameters for the Synthesised COPUFs – – – 135
5.3.2 Density and Water Absorption of COPUFs – – – – 137
5.3.3 Effect of Filler Incorporation on the Physico-chemical Properties
of COPUFs – – – – – – – – 138
5.3.4 Effect of Plasticisation on the Physical Properties of COPUFs – – 139
5.4 Mechanical Properties of COPUFs – – – – – 140
5.4.1 Compressive Strength – – – – – – – – 140
5.4.1 (a) Effect of Filler Loading on the Compressive Strength of COPUFs – 141
5.4.1 (b) Effect of Plasticiser Concentration on the Compressive Strength of
COPUFs – – – – – – – – – 141
5.4.2 Creep Recovery – – – – – – – – 142
xviii
5.4.3 Effect of Density on Mechanical Properties of COPUFs – – 143
5.5 Comparison of Physico-mechanical Properties of COPUFs with Standard
Values for the Conventional Polyurethane Foam- – – – 144
5.6 Flame Properties of COPUFs – – – – – – 145
5.6.1 Efefct of Foam Density on Flame Properties of COPUFs – – 145
5.6.2 Effect of FR Concentration on Flame Properties of COPUFs – – 146
5.6.3 Effect of HCTD/HCHD Blending on Flame Properties of COPUFs – 147
5.6.4 Effect of Filler Loading on Flame Properties of COPUFs – – 148
5.7 Morphological Characteristics of COPUFs – – – – 148
5.7.1 Effect of Modifier Concentration on the Morphology of GMFs – 149
5.7.2 Effect of Filler Concentration on the Morphology of CFFs – – 149
5.7.3 Effect of HCTD/HCHD Plasticisation on the Morphology of COPUFs 150
CHAPTER SIX: SUMMARY, CONCLUSION AND RECOMMENDATIONS
6.1 Summary – – – – – – – – – 151
6.2 Conclusions – – – – – – – – 154
6.3 Recommendations/Suggestions for Further Studies – – – 156
References – – – – – – – – 158
Appendices – – – – – – – – 183
Publications – – – – – – – – – 189Title – – – – – – – – – – i
Declaration – – – – – – – – – ii
Certification – – – – – – – – – iii
Dedication – – – – – – – – – iv
Acknowledgements – – – – – – – – – v
Abstract – – – – – – – – – – vii
Table of Contents – – – – – – – – ix
List of Tables – – – – – – – – – xix
List of Figures – – – – – – – – xxii
List of Plates – – – – – – – – – xxvii
List of Appendices – – – – – – – – – xxix
List of Abbreviations – – – – – – – – – xxxi
CHAPTER ONE: INTRODUCTION
1.1 Preamble – – – – – – – – 1
1.2 Polymers Based on Vegetable Oils – – – – – 3
1.3 Castor Oil – – – – – – – – – 6
1.4 Glycerolysis of Castor Oil – – – – – – 10
x
1.5 Polyurethanes – – – – – – – – 10
1.6 Chemistry of Polyurethane Synthesis – – – – – 11 1.7 Polyurethane Foams (PUFs) – – – – – – 13
1.7.1 Cell Structure – – – – – – – – 15
1.8 Castor Oil-Based Polyurethane Foams (COPUFs) – – – 15
1.9 Polymer Foam Formulations – – – – – – 17
1.10 Structure-Property Relationship in Polymers – – – – 21
1.11 Effect of Filler Incorporation on Morphology and Structure of PUFs – 22
1.12 Flammability Characteristics of PUFs – – – – – 24
1.13 Mechanical Properties of Polymer Foams – – – – 26
1.14 Polymer Foam Geometry – – – – – – 26
1.15 Research Objectives of the Study – – – – – – 27
1.16 Statement of Research Problem – – – – – 28
1.17 Justification/Significance of the Study – – – – – 29
1.18 Contributions to Knowledge – – – – – – – 30
1.19 Scope/Limitations of the Study – – – – – – 30
CHAPTER TWO: LITERATURE REVIEW
2.1 Chemical Modification of Vegetable Oils for PUF Synthesis – – 32
2.2 Polyurethane Additives – – – – – – – 37
xi
2.2.1 Chain Extenders – – – – – – – 38
2.2.2 Fillers – – – – – – – – – 39
2.2.3 Flame Retardants (FRs) – – – – – – – 42
2.2.3.1 Mechanisms of Flame Retardant Action – – – – 43
2.2.4 Plasticisers – – – – – – – – 45
2.2.4.1 Classification of Plasticisers – – – – – – 46
2.2.4.2 Mechanisms of Plasticisation – – – – – – 47
2.3 Characterisation of PUF Properties – – – – – 50
2.3.1 Physico-chemical Properties – – – – – – 50
2.3.1.1 FTIR – – – – – – – – – 51
2.3.2 Mechanical Properties – – – – – – – 52
2.3.2.1 Basic Mechanical Properties of Polymers – – – – 52
2.3.2.1(a) Test Methods – – – – – – – 52
2.3.2.1(b) Tensile Strength (ASTM D 638) – – – – – 53
2.3.2.1(c) Stress-Strain Properties in Tension – – – – 53
2.3.2.1(d) Elastic Modulus – – – – – – – 54
2.3.2.1(e) Flexural Properties of Plastics – – – – – 54
2.3.2.1(f) Hardness (ASTM D 785) – – – – – – 54
2.3.2.1(g) Compressive Strength (ASTM D 695) – – – – 56
xii
2.3.2.2 Mechanical Properties of Solid PUFs – – – – – 55
2.3.2.2(a) Nature of Cell Structure and Orientation – – – – 56
2.3.2.2(b) Compression – – – – – – – 57
2.3.2.2(c) Tension – – – – – – – – 58
2.3.2.3 Factors Influencing Mechanical Properties of Solid Foams – – 58
2.3.3 Morphological Properties – – – – – – 60
2.4 Structure-Property Relationships in PUFs – – – – 63
CHAPTER THREE: MATERIALS AND METHODS
3.1 Materials – – – – – – – – – – 66
3.2 Equipment/machines Used – – – – – – 67 3.3 Methods – – – – – – – – – 67
3.3.1 Seed Collection and Preparation – – – – – 67
3.3.2 Determination of Moisture Content of Seeds – – – – 67
3.3.3 Extraction and Purification of Oil from Castor Bean – – 68
3.3.4 Characterisation of Oil from Castor Bean – – – – 68
3.3.4(a) Physical Analyses – – – – – – – 68
3.3.4(a)(i) pH Measurement – – – – – – – 68
3.3.4(a)(ii) Determination of Refractive Index (RI) – – – 69
xiii
3.3.4(a)(iii) Determination of Specific Gravity (SG) – – – – 69 3.3.4(a)(iv) Determination of Relative Viscosity (RV) – – – 69
3.3.4(b) Chemical Analyses – – – – – – – 70
3.3.4(b)(i) Determination of Acid Number (AN) – – – – 70
3.3.4(b)(ii) Determinationn of Hydroxyl Number (HN) – – – 70
3.3.4(b)(iii) Determination of Saponification Number (SN) – – – 71
3.3.4(b)(iv) Determination of Peroxide Number (PN) – – – 72
3.3.4(b)(v) Determination of Iodine Number (IN) – – – – 72
3.3.4(c) FITR Spectroscopic Analysis – – – – – 73
3.3.4(d) GC-MS Analysis – – – – – – – 73
3.3.4(d)(i) Fatty Acid Profile – – – – – – – 73
3.3.5 Chemical Modification of Castor Oil – – – – – 74
3.3.5(a) Sulphation – – – – – – – – 74
3.3.5(b) PCl5 Chlorination (by Substitution) – – – – – 75
3.3.5(c) Alcoholysis (Glycerolysis) of Castor Oil- – – – 75
3.3.6 Foam-making Procedure – – – – – – 76
3.3.7 Foam Testing – – – – – – – – 77
3.3.7(a) Visual Observation – – – – – – – 77
3.3.7(b) Density Determination – – – – – – 77
xiv
3.3.7(c) Water Absorption – – – – – – – 78
3.3.7(d) Determination of Mechanical Properties – – – – 78
3.3.7(d)(i) Compressive Strength – – – – – – 78
3.3.7(d)(ii) Creep Recovery – – – – – – 79
3.3.8 Flammability Studies – – – – – – 80
3.3.8(a) Flame Retardant (FR) Treatment – – – – – 80
3.3.8(b) Ignition Time (seconds) – – – – – – 80
3.3.8(c) Flame Propagation Rate (cm/s) – – – – – 81
3.3.8(d) After-glow Time (seconds) – – – – – – 81
3.3.8(e) Add-on (%) – – – – – – – – 81
3.3.9 Scanning Electron Microscopic (SEM) Analysis – – – 81
CHAPTER FOUR: RESULTS
4.1 Physico-chemical Properties of Castor Oil (CO) and Modified Castor Oil
Polyols (MCOPs) – – – – – – – – 83
4.1.1 Fatty Acid Composition of the Castor Oil – – – – 84
4.1.2 Physico-chemical Properties of the MCOPs – – – – 85
4.1.2 (a) Variation of Hydroxyl Number and Relative Viscosity in MCOPs – 87
4.1.2(b) Variation of Iodine Number in MCOPs – – – – 88
4.1.2(c) Variation of Hydroxyl Number with Reaction Time during Polyol
xv
Synthesis – – – – – – – – 89
4.1.2(d) Results of FTIR and GC-MS Analysis of the MCOPs – – 90
4.1.2(d)(i) FTIR Spectra – – – – – – – 90
4.1.2(d)(ii) GC-MS Chromatograms – – – – – 95
4.2 Physical Properties of COPUFs- – – – – – 97
4.2.1 Density and Water Absorption of COPUFs – – – – 99
4.2.2 Effect of Filler Incorporation on the Physico-Chemical Properties of COPUFs 100
4.2.3 Comparison of Water Absorption of GMFs, PMFs and CFFs of
20wt% concentration of different NCO/OH ration – – – – 102
4.2.4 Effect of Plasticisation on the Physical Properties of COPUFs – – 103
4.3 Mechanical Properties of COPUFs – – – – – 104
4.3.1 Compressive Strength – – – – – – – 104
4.3.1(a) Effect of Plasticisation on the Compressive Strength of COPUFs 105
4.3.2 Creep Recovery – – – – – – – – 106
4.3.3 Effect of Density on Mechanical Properties of COPUFs – – 108
4.4 Comparison of Physico-mechamical Properties of COPUFs with Standard
Values for the Conventional PUF – – – – – 111
4.5 Flame Properties of COPUFs – – – – – – 111
4.5.1 Effect of Foam Density/Modifier Concentration on Flame Properties
of GMFs – – – – – – – – 112
xvi
4.5.2 Effect of FR Concentration on Flame Properties of COPUFs – – 115
4.5.3 Effect of HCTD/HCHD Blending on Flame Properties of COPUFs 117
4.5.4 Effect of Filler Loading on Flmae Properties of COPUFs – – 118
4.6 Morphological Characteristics of COPUFs – – – – 119
4.6.1 Effect of Modifier Concentration on the Morphology of GMFs – 120
4.6.2 Effect of Filler Concentration on the Morphology of CFFs – – 121
4.6.3 Effect of HCTD/HCHD Plasticisation on the Morphology of COPUFs 123
4.6.4 COPUF Pore Dimensions – – – – – – 123
CHAPTER FIVE: DISCUSSION
5.1 Physico-chemical properties of Castor Seed Oil – – – – 124
5.1.1 Physico-chemical Parameters – – – – – – 124
5.1.2 Results of FITR Analysis – – – – – – – 125
5.1.3 Results GC-MS Analysis – – – – – – 126
5.1.3 (a) Fatty Acid (FA) Composition – – – – – 126
5.2 Physico-chemical Properties of MCOPs – – – – – 127
5.2.1 Variation of Hydroxyl Number (HN) and Relative Visccosity (RV)
in MCOPs- – – – – – – – – 128
5.2.2 Variation of Iodine Number (IN) in MCOPs- – – – – 129
5.2.3 Variation of Hydroxyl Number with Reaction Time during Polyol
xvii
Synthesis – – – – – – – – – 130
5.2.4 Results of FTIR and GC-MS Analyses for the MCOPs – – 131
5.2.4 (a) GMCOPs – – – – – – – – 131
5.2.4 (b) PMCOPs – – – – – – – – 132
5.2.4 (b) (i) FTIR – – – – – – – – 132
5.2.4 (b) (ii) GC-MS – – – – – – – – 133
5.2.4 (c ) Sulphated Castor Oil (SLCO) – – – – – 134
5.3 Physical Properties of COPUFs – – – – – – 134
5.3.1 Process Parameters for the Synthesised COPUFs – – – 135
5.3.2 Density and Water Absorption of COPUFs – – – – 137
5.3.3 Effect of Filler Incorporation on the Physico-chemical Properties
of COPUFs – – – – – – – – 138
5.3.4 Effect of Plasticisation on the Physical Properties of COPUFs – – 139
5.4 Mechanical Properties of COPUFs – – – – – 140
5.4.1 Compressive Strength – – – – – – – – 140
5.4.1 (a) Effect of Filler Loading on the Compressive Strength of COPUFs – 141
5.4.1 (b) Effect of Plasticiser Concentration on the Compressive Strength of
COPUFs – – – – – – – – – 141
5.4.2 Creep Recovery – – – – – – – – 142
xviii
5.4.3 Effect of Density on Mechanical Properties of COPUFs – – 143
5.5 Comparison of Physico-mechanical Properties of COPUFs with Standard
Values for the Conventional Polyurethane Foam- – – – 144
5.6 Flame Properties of COPUFs – – – – – – 145
5.6.1 Efefct of Foam Density on Flame Properties of COPUFs – – 145
5.6.2 Effect of FR Concentration on Flame Properties of COPUFs – – 146
5.6.3 Effect of HCTD/HCHD Blending on Flame Properties of COPUFs – 147
5.6.4 Effect of Filler Loading on Flame Properties of COPUFs – – 148
5.7 Morphological Characteristics of COPUFs – – – – 148
5.7.1 Effect of Modifier Concentration on the Morphology of GMFs – 149
5.7.2 Effect of Filler Concentration on the Morphology of CFFs – – 149
5.7.3 Effect of HCTD/HCHD Plasticisation on the Morphology of COPUFs 150
CHAPTER SIX: SUMMARY, CONCLUSION AND RECOMMENDATIONS
6.1 Summary – – – – – – – – – 151
6.2 Conclusions – – – – – – – – 154
6.3 Recommendations/Suggestions for Further Studies – – – 156
References – – – – – – – – 158
Appendices – – – – – – – – 183
Publications – – – – – – – – – 189Title – – – – – – – – – – i
Declaration – – – – – – – – – ii
Certification – – – – – – – – – iii
Dedication – – – – – – – – – iv
Acknowledgements – – – – – – – – – v
Abstract – – – – – – – – – – vii
Table of Contents – – – – – – – – ix
List of Tables – – – – – – – – – xix
List of Figures – – – – – – – – xxii
List of Plates – – – – – – – – – xxvii
List of Appendices – – – – – – – – – xxix
List of Abbreviations – – – – – – – – – xxxi
CHAPTER ONE: INTRODUCTION
1.1 Preamble – – – – – – – – 1
1.2 Polymers Based on Vegetable Oils – – – – – 3
1.3 Castor Oil – – – – – – – – – 6
1.4 Glycerolysis of Castor Oil – – – – – – 10
x
1.5 Polyurethanes – – – – – – – – 10
1.6 Chemistry of Polyurethane Synthesis – – – – – 11 1.7 Polyurethane Foams (PUFs) – – – – – – 13
1.7.1 Cell Structure – – – – – – – – 15
1.8 Castor Oil-Based Polyurethane Foams (COPUFs) – – – 15
1.9 Polymer Foam Formulations – – – – – – 17
1.10 Structure-Property Relationship in Polymers – – – – 21
1.11 Effect of Filler Incorporation on Morphology and Structure of PUFs – 22
1.12 Flammability Characteristics of PUFs – – – – – 24
1.13 Mechanical Properties of Polymer Foams – – – – 26
1.14 Polymer Foam Geometry – – – – – – 26
1.15 Research Objectives of the Study – – – – – – 27
1.16 Statement of Research Problem – – – – – 28
1.17 Justification/Significance of the Study – – – – – 29
1.18 Contributions to Knowledge – – – – – – – 30
1.19 Scope/Limitations of the Study – – – – – – 30
CHAPTER TWO: LITERATURE REVIEW
2.1 Chemical Modification of Vegetable Oils for PUF Synthesis – – 32
2.2 Polyurethane Additives – – – – – – – 37
xi
2.2.1 Chain Extenders – – – – – – – 38
2.2.2 Fillers – – – – – – – – – 39
2.2.3 Flame Retardants (FRs) – – – – – – – 42
2.2.3.1 Mechanisms of Flame Retardant Action – – – – 43
2.2.4 Plasticisers – – – – – – – – 45
2.2.4.1 Classification of Plasticisers – – – – – – 46
2.2.4.2 Mechanisms of Plasticisation – – – – – – 47
2.3 Characterisation of PUF Properties – – – – – 50
2.3.1 Physico-chemical Properties – – – – – – 50
2.3.1.1 FTIR – – – – – – – – – 51
2.3.2 Mechanical Properties – – – – – – – 52
2.3.2.1 Basic Mechanical Properties of Polymers – – – – 52
2.3.2.1(a) Test Methods – – – – – – – 52
2.3.2.1(b) Tensile Strength (ASTM D 638) – – – – – 53
2.3.2.1(c) Stress-Strain Properties in Tension – – – – 53
2.3.2.1(d) Elastic Modulus – – – – – – – 54
2.3.2.1(e) Flexural Properties of Plastics – – – – – 54
2.3.2.1(f) Hardness (ASTM D 785) – – – – – – 54
2.3.2.1(g) Compressive Strength (ASTM D 695) – – – – 56
xii
2.3.2.2 Mechanical Properties of Solid PUFs – – – – – 55
2.3.2.2(a) Nature of Cell Structure and Orientation – – – – 56
2.3.2.2(b) Compression – – – – – – – 57
2.3.2.2(c) Tension – – – – – – – – 58
2.3.2.3 Factors Influencing Mechanical Properties of Solid Foams – – 58
2.3.3 Morphological Properties – – – – – – 60
2.4 Structure-Property Relationships in PUFs – – – – 63
CHAPTER THREE: MATERIALS AND METHODS
3.1 Materials – – – – – – – – – – 66
3.2 Equipment/machines Used – – – – – – 67 3.3 Methods – – – – – – – – – 67
3.3.1 Seed Collection and Preparation – – – – – 67
3.3.2 Determination of Moisture Content of Seeds – – – – 67
3.3.3 Extraction and Purification of Oil from Castor Bean – – 68
3.3.4 Characterisation of Oil from Castor Bean – – – – 68
3.3.4(a) Physical Analyses – – – – – – – 68
3.3.4(a)(i) pH Measurement – – – – – – – 68
3.3.4(a)(ii) Determination of Refractive Index (RI) – – – 69
xiii
3.3.4(a)(iii) Determination of Specific Gravity (SG) – – – – 69 3.3.4(a)(iv) Determination of Relative Viscosity (RV) – – – 69
3.3.4(b) Chemical Analyses – – – – – – – 70
3.3.4(b)(i) Determination of Acid Number (AN) – – – – 70
3.3.4(b)(ii) Determinationn of Hydroxyl Number (HN) – – – 70
3.3.4(b)(iii) Determination of Saponification Number (SN) – – – 71
3.3.4(b)(iv) Determination of Peroxide Number (PN) – – – 72
3.3.4(b)(v) Determination of Iodine Number (IN) – – – – 72
3.3.4(c) FITR Spectroscopic Analysis – – – – – 73
3.3.4(d) GC-MS Analysis – – – – – – – 73
3.3.4(d)(i) Fatty Acid Profile – – – – – – – 73
3.3.5 Chemical Modification of Castor Oil – – – – – 74
3.3.5(a) Sulphation – – – – – – – – 74
3.3.5(b) PCl5 Chlorination (by Substitution) – – – – – 75
3.3.5(c) Alcoholysis (Glycerolysis) of Castor Oil- – – – 75
3.3.6 Foam-making Procedure – – – – – – 76
3.3.7 Foam Testing – – – – – – – – 77
3.3.7(a) Visual Observation – – – – – – – 77
3.3.7(b) Density Determination – – – – – – 77
xiv
3.3.7(c) Water Absorption – – – – – – – 78
3.3.7(d) Determination of Mechanical Properties – – – – 78
3.3.7(d)(i) Compressive Strength – – – – – – 78
3.3.7(d)(ii) Creep Recovery – – – – – – 79
3.3.8 Flammability Studies – – – – – – 80
3.3.8(a) Flame Retardant (FR) Treatment – – – – – 80
3.3.8(b) Ignition Time (seconds) – – – – – – 80
3.3.8(c) Flame Propagation Rate (cm/s) – – – – – 81
3.3.8(d) After-glow Time (seconds) – – – – – – 81
3.3.8(e) Add-on (%) – – – – – – – – 81
3.3.9 Scanning Electron Microscopic (SEM) Analysis – – – 81
CHAPTER FOUR: RESULTS
4.1 Physico-chemical Properties of Castor Oil (CO) and Modified Castor Oil
Polyols (MCOPs) – – – – – – – – 83
4.1.1 Fatty Acid Composition of the Castor Oil – – – – 84
4.1.2 Physico-chemical Properties of the MCOPs – – – – 85
4.1.2 (a) Variation of Hydroxyl Number and Relative Viscosity in MCOPs – 87
4.1.2(b) Variation of Iodine Number in MCOPs – – – – 88
4.1.2(c) Variation of Hydroxyl Number with Reaction Time during Polyol
xv
Synthesis – – – – – – – – 89
4.1.2(d) Results of FTIR and GC-MS Analysis of the MCOPs – – 90
4.1.2(d)(i) FTIR Spectra – – – – – – – 90
4.1.2(d)(ii) GC-MS Chromatograms – – – – – 95
4.2 Physical Properties of COPUFs- – – – – – 97
4.2.1 Density and Water Absorption of COPUFs – – – – 99
4.2.2 Effect of Filler Incorporation on the Physico-Chemical Properties of COPUFs 100
4.2.3 Comparison of Water Absorption of GMFs, PMFs and CFFs of
20wt% concentration of different NCO/OH ration – – – – 102
4.2.4 Effect of Plasticisation on the Physical Properties of COPUFs – – 103
4.3 Mechanical Properties of COPUFs – – – – – 104
4.3.1 Compressive Strength – – – – – – – 104
4.3.1(a) Effect of Plasticisation on the Compressive Strength of COPUFs 105
4.3.2 Creep Recovery – – – – – – – – 106
4.3.3 Effect of Density on Mechanical Properties of COPUFs – – 108
4.4 Comparison of Physico-mechamical Properties of COPUFs with Standard
Values for the Conventional PUF – – – – – 111
4.5 Flame Properties of COPUFs – – – – – – 111
4.5.1 Effect of Foam Density/Modifier Concentration on Flame Properties
of GMFs – – – – – – – – 112
xvi
4.5.2 Effect of FR Concentration on Flame Properties of COPUFs – – 115
4.5.3 Effect of HCTD/HCHD Blending on Flame Properties of COPUFs 117
4.5.4 Effect of Filler Loading on Flmae Properties of COPUFs – – 118
4.6 Morphological Characteristics of COPUFs – – – – 119
4.6.1 Effect of Modifier Concentration on the Morphology of GMFs – 120
4.6.2 Effect of Filler Concentration on the Morphology of CFFs – – 121
4.6.3 Effect of HCTD/HCHD Plasticisation on the Morphology of COPUFs 123
4.6.4 COPUF Pore Dimensions – – – – – – 123
CHAPTER FIVE: DISCUSSION
5.1 Physico-chemical properties of Castor Seed Oil – – – – 124
5.1.1 Physico-chemical Parameters – – – – – – 124
5.1.2 Results of FITR Analysis – – – – – – – 125
5.1.3 Results GC-MS Analysis – – – – – – 126
5.1.3 (a) Fatty Acid (FA) Composition – – – – – 126
5.2 Physico-chemical Properties of MCOPs – – – – – 127
5.2.1 Variation of Hydroxyl Number (HN) and Relative Visccosity (RV)
in MCOPs- – – – – – – – – 128
5.2.2 Variation of Iodine Number (IN) in MCOPs- – – – – 129
5.2.3 Variation of Hydroxyl Number with Reaction Time during Polyol
xvii
Synthesis – – – – – – – – – 130
5.2.4 Results of FTIR and GC-MS Analyses for the MCOPs – – 131
5.2.4 (a) GMCOPs – – – – – – – – 131
5.2.4 (b) PMCOPs – – – – – – – – 132
5.2.4 (b) (i) FTIR – – – – – – – – 132
5.2.4 (b) (ii) GC-MS – – – – – – – – 133
5.2.4 (c ) Sulphated Castor Oil (SLCO) – – – – – 134
5.3 Physical Properties of COPUFs – – – – – – 134
5.3.1 Process Parameters for the Synthesised COPUFs – – – 135
5.3.2 Density and Water Absorption of COPUFs – – – – 137
5.3.3 Effect of Filler Incorporation on the Physico-chemical Properties
of COPUFs – – – – – – – – 138
5.3.4 Effect of Plasticisation on the Physical Properties of COPUFs – – 139
5.4 Mechanical Properties of COPUFs – – – – – 140
5.4.1 Compressive Strength – – – – – – – – 140
5.4.1 (a) Effect of Filler Loading on the Compressive Strength of COPUFs – 141
5.4.1 (b) Effect of Plasticiser Concentration on the Compressive Strength of
COPUFs – – – – – – – – – 141
5.4.2 Creep Recovery – – – – – – – – 142
xviii
5.4.3 Effect of Density on Mechanical Properties of COPUFs – – 143
5.5 Comparison of Physico-mechanical Properties of COPUFs with Standard
Values for the Conventional Polyurethane Foam- – – – 144
5.6 Flame Properties of COPUFs – – – – – – 145
5.6.1 Efefct of Foam Density on Flame Properties of COPUFs – – 145
5.6.2 Effect of FR Concentration on Flame Properties of COPUFs – – 146
5.6.3 Effect of HCTD/HCHD Blending on Flame Properties of COPUFs – 147
5.6.4 Effect of Filler Loading on Flame Properties of COPUFs – – 148
5.7 Morphological Characteristics of COPUFs – – – – 148
5.7.1 Effect of Modifier Concentration on the Morphology of GMFs – 149
5.7.2 Effect of Filler Concentration on the Morphology of CFFs – – 149
5.7.3 Effect of HCTD/HCHD Plasticisation on the Morphology of COPUFs 150
CHAPTER SIX: SUMMARY, CONCLUSION AND RECOMMENDATIONS
6.1 Summary – – – – – – – – – 151
6.2 Conclusions – – – – – – – – 154
6.3 Recommendations/Suggestions for Further Studies – – – 156
References – – – – – – – – 158
Appendices – – – – – – – – 183
Publications – – – – – – – – – 189Title – – – – – – – – – – i
Declaration – – – – – – – – – ii
Certification – – – – – – – – – iii
Dedication – – – – – – – – – iv
Acknowledgements – – – – – – – – – v
Abstract – – – – – – – – – – vii
Table of Contents – – – – – – – – ix
List of Tables – – – – – – – – – xix
List of Figures – – – – – – – – xxii
List of Plates – – – – – – – – – xxvii
List of Appendices – – – – – – – – – xxix
List of Abbreviations – – – – – – – – – xxxi
CHAPTER ONE: INTRODUCTION
1.1 Preamble – – – – – – – – 1
1.2 Polymers Based on Vegetable Oils – – – – – 3
1.3 Castor Oil – – – – – – – – – 6
1.4 Glycerolysis of Castor Oil – – – – – – 10
x
1.5 Polyurethanes – – – – – – – – 10
1.6 Chemistry of Polyurethane Synthesis – – – – – 11 1.7 Polyurethane Foams (PUFs) – – – – – – 13
1.7.1 Cell Structure – – – – – – – – 15
1.8 Castor Oil-Based Polyurethane Foams (COPUFs) – – – 15
1.9 Polymer Foam Formulations – – – – – – 17
1.10 Structure-Property Relationship in Polymers – – – – 21
1.11 Effect of Filler Incorporation on Morphology and Structure of PUFs – 22
1.12 Flammability Characteristics of PUFs – – – – – 24
1.13 Mechanical Properties of Polymer Foams – – – – 26
1.14 Polymer Foam Geometry – – – – – – 26
1.15 Research Objectives of the Study – – – – – – 27
1.16 Statement of Research Problem – – – – – 28
1.17 Justification/Significance of the Study – – – – – 29
1.18 Contributions to Knowledge – – – – – – – 30
1.19 Scope/Limitations of the Study – – – – – – 30
CHAPTER TWO: LITERATURE REVIEW
2.1 Chemical Modification of Vegetable Oils for PUF Synthesis – – 32
2.2 Polyurethane Additives – – – – – – – 37
xi
2.2.1 Chain Extenders – – – – – – – 38
2.2.2 Fillers – – – – – – – – – 39
2.2.3 Flame Retardants (FRs) – – – – – – – 42
2.2.3.1 Mechanisms of Flame Retardant Action – – – – 43
2.2.4 Plasticisers – – – – – – – – 45
2.2.4.1 Classification of Plasticisers – – – – – – 46
2.2.4.2 Mechanisms of Plasticisation – – – – – – 47
2.3 Characterisation of PUF Properties – – – – – 50
2.3.1 Physico-chemical Properties – – – – – – 50
2.3.1.1 FTIR – – – – – – – – – 51
2.3.2 Mechanical Properties – – – – – – – 52
2.3.2.1 Basic Mechanical Properties of Polymers – – – – 52
2.3.2.1(a) Test Methods – – – – – – – 52
2.3.2.1(b) Tensile Strength (ASTM D 638) – – – – – 53
2.3.2.1(c) Stress-Strain Properties in Tension – – – – 53
2.3.2.1(d) Elastic Modulus – – – – – – – 54
2.3.2.1(e) Flexural Properties of Plastics – – – – – 54
2.3.2.1(f) Hardness (ASTM D 785) – – – – – – 54
2.3.2.1(g) Compressive Strength (ASTM D 695) – – – – 56
xii
2.3.2.2 Mechanical Properties of Solid PUFs – – – – – 55
2.3.2.2(a) Nature of Cell Structure and Orientation – – – – 56
2.3.2.2(b) Compression – – – – – – – 57
2.3.2.2(c) Tension – – – – – – – – 58
2.3.2.3 Factors Influencing Mechanical Properties of Solid Foams – – 58
2.3.3 Morphological Properties – – – – – – 60
2.4 Structure-Property Relationships in PUFs – – – – 63
CHAPTER THREE: MATERIALS AND METHODS
3.1 Materials – – – – – – – – – – 66
3.2 Equipment/machines Used – – – – – – 67 3.3 Methods – – – – – – – – – 67
3.3.1 Seed Collection and Preparation – – – – – 67
3.3.2 Determination of Moisture Content of Seeds – – – – 67
3.3.3 Extraction and Purification of Oil from Castor Bean – – 68
3.3.4 Characterisation of Oil from Castor Bean – – – – 68
3.3.4(a) Physical Analyses – – – – – – – 68
3.3.4(a)(i) pH Measurement – – – – – – – 68
3.3.4(a)(ii) Determination of Refractive Index (RI) – – – 69
xiii
3.3.4(a)(iii) Determination of Specific Gravity (SG) – – – – 69 3.3.4(a)(iv) Determination of Relative Viscosity (RV) – – – 69
3.3.4(b) Chemical Analyses – – – – – – – 70
3.3.4(b)(i) Determination of Acid Number (AN) – – – – 70
3.3.4(b)(ii) Determinationn of Hydroxyl Number (HN) – – – 70
3.3.4(b)(iii) Determination of Saponification Number (SN) – – – 71
3.3.4(b)(iv) Determination of Peroxide Number (PN) – – – 72
3.3.4(b)(v) Determination of Iodine Number (IN) – – – – 72
3.3.4(c) FITR Spectroscopic Analysis – – – – – 73
3.3.4(d) GC-MS Analysis – – – – – – – 73
3.3.4(d)(i) Fatty Acid Profile – – – – – – – 73
3.3.5 Chemical Modification of Castor Oil – – – – – 74
3.3.5(a) Sulphation – – – – – – – – 74
3.3.5(b) PCl5 Chlorination (by Substitution) – – – – – 75
3.3.5(c) Alcoholysis (Glycerolysis) of Castor Oil- – – – 75
3.3.6 Foam-making Procedure – – – – – – 76
3.3.7 Foam Testing – – – – – – – – 77
3.3.7(a) Visual Observation – – – – – – – 77
3.3.7(b) Density Determination – – – – – – 77
xiv
3.3.7(c) Water Absorption – – – – – – – 78
3.3.7(d) Determination of Mechanical Properties – – – – 78
3.3.7(d)(i) Compressive Strength – – – – – – 78
3.3.7(d)(ii) Creep Recovery – – – – – – 79
3.3.8 Flammability Studies – – – – – – 80
3.3.8(a) Flame Retardant (FR) Treatment – – – – – 80
3.3.8(b) Ignition Time (seconds) – – – – – – 80
3.3.8(c) Flame Propagation Rate (cm/s) – – – – – 81
3.3.8(d) After-glow Time (seconds) – – – – – – 81
3.3.8(e) Add-on (%) – – – – – – – – 81
3.3.9 Scanning Electron Microscopic (SEM) Analysis – – – 81
CHAPTER FOUR: RESULTS
4.1 Physico-chemical Properties of Castor Oil (CO) and Modified Castor Oil
Polyols (MCOPs) – – – – – – – – 83
4.1.1 Fatty Acid Composition of the Castor Oil – – – – 84
4.1.2 Physico-chemical Properties of the MCOPs – – – – 85
4.1.2 (a) Variation of Hydroxyl Number and Relative Viscosity in MCOPs – 87
4.1.2(b) Variation of Iodine Number in MCOPs – – – – 88
4.1.2(c) Variation of Hydroxyl Number with Reaction Time during Polyol
xv
Synthesis – – – – – – – – 89
4.1.2(d) Results of FTIR and GC-MS Analysis of the MCOPs – – 90
4.1.2(d)(i) FTIR Spectra – – – – – – – 90
4.1.2(d)(ii) GC-MS Chromatograms – – – – – 95
4.2 Physical Properties of COPUFs- – – – – – 97
4.2.1 Density and Water Absorption of COPUFs – – – – 99
4.2.2 Effect of Filler Incorporation on the Physico-Chemical Properties of COPUFs 100
4.2.3 Comparison of Water Absorption of GMFs, PMFs and CFFs of
20wt% concentration of different NCO/OH ration – – – – 102
4.2.4 Effect of Plasticisation on the Physical Properties of COPUFs – – 103
4.3 Mechanical Properties of COPUFs – – – – – 104
4.3.1 Compressive Strength – – – – – – – 104
4.3.1(a) Effect of Plasticisation on the Compressive Strength of COPUFs 105
4.3.2 Creep Recovery – – – – – – – – 106
4.3.3 Effect of Density on Mechanical Properties of COPUFs – – 108
4.4 Comparison of Physico-mechamical Properties of COPUFs with Standard
Values for the Conventional PUF – – – – – 111
4.5 Flame Properties of COPUFs – – – – – – 111
4.5.1 Effect of Foam Density/Modifier Concentration on Flame Properties
of GMFs – – – – – – – – 112
xvi
4.5.2 Effect of FR Concentration on Flame Properties of COPUFs – – 115
4.5.3 Effect of HCTD/HCHD Blending on Flame Properties of COPUFs 117
4.5.4 Effect of Filler Loading on Flmae Properties of COPUFs – – 118
4.6 Morphological Characteristics of COPUFs – – – – 119
4.6.1 Effect of Modifier Concentration on the Morphology of GMFs – 120
4.6.2 Effect of Filler Concentration on the Morphology of CFFs – – 121
4.6.3 Effect of HCTD/HCHD Plasticisation on the Morphology of COPUFs 123
4.6.4 COPUF Pore Dimensions – – – – – – 123
CHAPTER FIVE: DISCUSSION
5.1 Physico-chemical properties of Castor Seed Oil – – – – 124
5.1.1 Physico-chemical Parameters – – – – – – 124
5.1.2 Results of FITR Analysis – – – – – – – 125
5.1.3 Results GC-MS Analysis – – – – – – 126
5.1.3 (a) Fatty Acid (FA) Composition – – – – – 126
5.2 Physico-chemical Properties of MCOPs – – – – – 127
5.2.1 Variation of Hydroxyl Number (HN) and Relative Visccosity (RV)
in MCOPs- – – – – – – – – 128
5.2.2 Variation of Iodine Number (IN) in MCOPs- – – – – 129
5.2.3 Variation of Hydroxyl Number with Reaction Time during Polyol
xvii
Synthesis – – – – – – – – – 130
5.2.4 Results of FTIR and GC-MS Analyses for the MCOPs – – 131
5.2.4 (a) GMCOPs – – – – – – – – 131
5.2.4 (b) PMCOPs – – – – – – – – 132
5.2.4 (b) (i) FTIR – – – – – – – – 132
5.2.4 (b) (ii) GC-MS – – – – – – – – 133
5.2.4 (c ) Sulphated Castor Oil (SLCO) – – – – – 134
5.3 Physical Properties of COPUFs – – – – – – 134
5.3.1 Process Parameters for the Synthesised COPUFs – – – 135
5.3.2 Density and Water Absorption of COPUFs – – – – 137
5.3.3 Effect of Filler Incorporation on the Physico-chemical Properties
of COPUFs – – – – – – – – 138
5.3.4 Effect of Plasticisation on the Physical Properties of COPUFs – – 139
5.4 Mechanical Properties of COPUFs – – – – – 140
5.4.1 Compressive Strength – – – – – – – – 140
5.4.1 (a) Effect of Filler Loading on the Compressive Strength of COPUFs – 141
5.4.1 (b) Effect of Plasticiser Concentration on the Compressive Strength of
COPUFs – – – – – – – – – 141
5.4.2 Creep Recovery – – – – – – – – 142
xviii
5.4.3 Effect of Density on Mechanical Properties of COPUFs – – 143
5.5 Comparison of Physico-mechanical Properties of COPUFs with Standard
Values for the Conventional Polyurethane Foam- – – – 144
5.6 Flame Properties of COPUFs – – – – – – 145
5.6.1 Efefct of Foam Density on Flame Properties of COPUFs – – 145
5.6.2 Effect of FR Concentration on Flame Properties of COPUFs – – 146
5.6.3 Effect of HCTD/HCHD Blending on Flame Properties of COPUFs – 147
5.6.4 Effect of Filler Loading on Flame Properties of COPUFs – – 148
5.7 Morphological Characteristics of COPUFs – – – – 148
5.7.1 Effect of Modifier Concentration on the Morphology of GMFs – 149
5.7.2 Effect of Filler Concentration on the Morphology of CFFs – – 149
5.7.3 Effect of HCTD/HCHD Plasticisation on the Morphology of COPUFs 150
CHAPTER SIX: SUMMARY, CONCLUSION AND RECOMMENDATIONS
6.1 Summary – – – – – – – – – 151
6.2 Conclusions – – – – – – – – 154
6.3 Recommendations/Suggestions for Further Studies – – – 156
References – – – – – – – – 158
Appendices – – – – – – – – 183
Publications – – – – – – – – – 189

 

 

CHAPTER ONE

INTRODUCTION
1.1 Preamble
Recent global surge in the quest for renewable natural resources of plant origin stems largely from their suitability and sustainability as chemical feedstock, as a result of the economic and environmental-safety advantages they have over petroleum-based feedstock. These advantages include widespread availability, low cost, non-toxicity, low emission properties and biodegradability (Sherman, 2007; Gupta et al., 2010; Petrovic and Cvetkovic, 2012). On the other hand, the use of fossilised carbon-based materials such as coal and petrol in the synthesis of polymeric materials and other products of the chemical industry has resulted in the gradual depletion of these reserves; increased emission of greenhouse gases and accumulation of non-biodegradable waste on earth, among other environmental impacts (Lochab et al., 2012).
Current sustainability research drive therefore is towards developing green source materials as potential replacements for petroleum-based feedstock. Vegetable oils definitely represent an important group of agricultural stock for this purpose. Within this group, soybean oil, castor oil, palm oil and canola oil are the most promising vegetable oils for the industrial development of bio-based materials (Husic et al., 2005; Luo et al., 2008; Jose et al; 2008). In terms of availability though, soybean, palm, rapeseed and sunflower oils are the most abundant (Zhang et al., 2007; Genova et al., 2008; Prociak, 2008). However, the use of non-edible vegetable oil like castor oil towards realising this goal obviously has other advantages related to food security. Moreover, world consumption of edible vegetable oils from 1995/1996 – 2014/2015, for
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instance, has been on a steady rise, reaching 173.27 million metric tons in 2014/2015 (Fig.1.1) (Statistica, 2015). Focus, therefore, ought to be more on the exploitation of the non-edible stock (such as castor and jatropha oils), while preserving the edible ones mainly for human consumption. Even then, there could still arise the problem of vast land areas needed to cultivate large plantations of the non-edible stock, which could otherwise have been used for the edibles (Mazubert et al., 2013).
This work represents a modest contribution, and an added impetus to the growing search for viable and sustainable options for replacing petroleum-based chemical feedstocks from among the more palatable and renewable bioresources of plant origin available. In Nigeria, the polyurethane (PU) foam industry is still stitched in mass importation of petro-polyols for PU foam production. This is costing the country large amounts of foreign exchange needed in other (more essential) sectors. Castor oil, non-edible and with its numerous advantages over other vegetable oils, is focused upon as a potential candidate for this replacement, especially in commercial PU development.
35%
27%
15%
9%
14%
Palm oil
Soybean oil
Canola oil
Sunflower oil
Others
Fig.1.1: Global vegetable oil consumption by type (2014/2015)
Source: Statistica (2015)
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1.2 Polymers Based on Vegetable Oils
Vegetable oils and fats belong to a large family of hydrophobic chemical compounds called lipids. The oils are made up of triglyceride molecules, each molecule comprising three fatty acids attached to a glycerol backbone. According to Stenberg (2013), fatty acids make up about 94 – 96% of the total weight of triglycerides. Therefore, the properties and reactivity of triglycerides strongly depend on their composition, chain length, degree of unsaturation, number, distribution and location of hydroxyl groups etc (Sharmin et al., 2012). In other words, vegetable oils are heterogeneous entities, with overall compositions and properties varying from oil to oil. Polymers can be synthesised from vegetable oils because the triglyceride molecules in the latter contain polymerisable sites or functional groups – usually double bonds, hydroxyl or epoxy groups. Various polymerisation reactions, including cationic, condensation, and radical copolymerisation reactions, have been used to produce different types of polymers such as polyesters, polyamides, epoxies and polyurethanes (PUs) (Del Rio, 2011).
Studies have shown that typical drying oils characterised by high unsaturation levels (notably linseed and tung oils) are transformed into hard, solid film-like materials on exposure to air for some time, because of the crosslinking between fatty acid (FA) chains through the atmospheric oxygen molecule (Taylor, 1950). For a very long time, drying oils have been used in oil paints and as surface-coating materials because of this property (Del Rio, 2011). However, for most vegetable oils, double bonds in triglycerides are not sufficiently reactive for any viable polymerisation process. Again, with the exception of castor and lesquerella oils, natural oils do not contain hydroxyls inherently (Appelqvist, 1989; Carlson et al., 1990). Therefore, chemical modification is needed to add hydroxyls to natural oils to produce so called natural oil polyols (NOPs).
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A polyol is a polymeric or oligomeric polyhydroxy compound of the type R (OH)n (n ≥ 2) that can be used as raw material in PU synthesis. High molecular weight polyols with low hydroxyl functionality yield flexible PUs with lower glass transition temperatures (Tgs) than those synthesised with lower molecular weight and high functionality polyols (Del Rio, 2011). Compared to petroleum-based polyols such as polyether and polyester polyols with hydroxyl numbers of up to 400-500mgKOH/g (Narine et al., 2007), NOPs typically have low hydroxyl functionalities and relatively high equivalent weights (Sherman, 2007).
Vegetable oils containing secondary hydroxyl groups that are located in the middle of their triglyceride alkyl chains have pendant or “dangling” chains exerting significant steric hindrance to crosslinking (thus incidentally acting as plasticiser) because they do not support stress under load (Guo et al., 2000; Xu et al., 2008; Fan et al., 2012). This has the effect of reducing PU rigidity (Zlatanic, 2002). Thus, although such vegetable oils (e.g. castor oil) can be polymerized directly by reacting their secondary hydroxyls with diisocyanate to yield PUs, or with carboxylates to obtain thermosetting polyesters (Guner, 2006; Petrovic, 2008), the PU products were found to be of low compressive strengths, low modulus, low resilience and high Tg (Ramirez et al.,2008; Del Rio, 2011; Bleys, 2012). Chemical modification has provided substantial remedy to all these. Recent efforts have been directed towards chemical modification of vegetable oils to produce useful, cheaper and environmentally friendly polymers compared to petro-polyols (Saremi et al., 2012). The modification introduces reactive groups into the FA chains to enhance polymerisability. This can be achieved by:
(1) Epoxidation, followed by oxirane ring opening (Okieimen et al., 2002;Tayde et al., 2011; Dworakowska et al., 2012).
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(2) Transesterification/alcoholysis using polyhydroxy compounds like glycerol, pentaerythritol etc (Schuchardt et al., 1998; Chakrabarti and Rafiq, 2008).
(3) Hydroformylation or ozonolysis, and subsequent hydrogenation (Narine et al., 2007).
(4) Halogen addition and nucleophilic substitution (Guo et al., 2000).
(5) Treatment with maleic anhydride to attach maleates (Eren et al., 2003).
(6) Enzymatic/microbial conversion (McNeil and Berger, 1993).
Chemical modifications make vegetable oils polymerisable because of the introduction of new and usually more reactive functional groups such as hydroxyls, epoxies or carboxyls (Del Rio, 2011). They also confer on the synthesised polymers enhanced structure and physical properties, in addition to imparting other desired characteristics on them. Many research studies on vegetable oil-based PUs have been performed in the last few decades. Vegetable oils, as renewable bioresources, are fast replacing conventional petroleum-based polyols in PU synthesis (Petrovic, 2008; Babb, 2012; Zhang et al., 2013).
In the polymer and chemical industry, vegetable oils which represent a major potential source of chemicals have been utilised as alternative feedstock for monomers in the production of biopolymers with diverse properties and applications. As polymers are widely used both in industry and daily life, they are quantitatively the most important products of the chemical industry. However, while most petroleum-based polymers are non-recyclable, polymers based on vegetable oils largely are (Fig. 1.2).
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Fig.1.2: Life cycle of vegetable oil-based biopolymers
1.3 Castor Oil
Castor oil (CO) is a colourless to pale yellow vegetable oil derived from the castor plant (Ricinus communis Linn) belonging to the family Euphorbiaceae. The plant thrives well in tropical, subtropical and even warm temperate regions of the world (Salunke and Desai, 1992; Ogunniyi, 2006; Salihu et al., 2014), in addition to being drought and pest resistant. Global castor seed production is over one million tons per annum, with India, China and Brazil as major producers. In Nigeria, the castor plant is widely available throughout the country- but largely as uncultivated weed growing wild on marginal lands. The only reported (small scale) cultivation of the crop was in Kogi State, Nigeria (Dalen et al., 2014), and in the eastern part of the country where the castor seed is popularly used as food condiment called ogiri after treatment and detoxification by fermentation (Achi, 2005).
Processing
Extraction
Use
VEGETABLE
OILS
Modification
Synthesis
BIOPOLYMERS
WASTE
Recycling
BIOMASS
Biodegradation
Assimilation
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Castor seed oil is extracted from dehulled and processed castor beans by mechanical
expression (usually by hydraulic pressing or continuous screw pressing), solvent
extraction or both. Mechanically extracted castor oil may be cold- or hot- pressed.
Processing of castor beans involves a sequence of operations that may include pod or
seed coat removal, winnowing, sorting, cleaning, grinding or milling, pre-heating etc.
(Akpan et al., 2006; Alirezalu et al., 2011; CastorOil.in, 2015). Average oil content for
all castor seed varieties is about 46-55% (Ogunniyi, 2006). Oil yield, oil composition
and quality will depend on seed variety and quality, as well as geographic origin and
climatic conditions around the resource castor crop (Ogunniyi, 2006; Alirezalu et al.,
2011; Oluwole et al., 2015). Oil yield and recovery will also depend on the extraction
method (s) used and the prevailing extraction conditions (Olaniyan, 2010).
Castor oil, a trifunctional vegetable oil, is distinguished from other vegetable oils by its
high content (87-90%) of C-18 monounsaturated ricinoleic acid, and relatively high
acetyl or hydroxyl value (Ogunniyi, 2006; Conceicao et al., 2007).
The oil also contains other fatty acids that include oleic, linoleic, stearic, palmitic and
linolenic acids (Table 1.1).
Fig.1. 3: Structure of castor oil triglyceride
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Table 1.1: Fatty acid composition in castor oil (Dave, 2002)
Weight% Fatty acid Structure
High ricinoleic acid content gives castor oil high degree of purity. The chemistry of
castor oil is centred on its high ricinoleic acid content, and the three main reaction sites
or functional groups in the triglyceride molecules.
Specifically, the ester linkages, the double bonds and hydroxyl groups in the oil provide
reaction sites for the preparation of many useful castor oil derivatives. The presence of
hydroxyl groups in the oil‟s fatty acid structure (Fig. 1.3) is responsible for urethane
type reactions with diisocynate for PU synthesis. The oil‟s long (C-18) carbon chain
confer on it high thermal and hydrolytic stability, with the result that polymers derived
from it exhibit high resistance to heat and humidity (Javni et al., 2000; Zlatanic et al.,
2002; CastorOil.in, 2015). The oil is therefore naturally an excellent biorenewable raw
material for PU development. Castor oil has a growing international market assured by
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more than 700 uses ranging from medicines to cosmetics, to substituting petroleum in the production of biodiesel, plastics and lubricants (Weiss, 2000; CIREP, 2007). This makes the oil versatile seed oil with very high utilitarian value compared to other vegetable oils.
However, castor oil‟s hydroxyl number of 160-168 (WHC, 2012) is rather low, and its hydroxyl groups are secondary hydroxyls. It is known that isocyanate reacts faster with primary hydroxyl groups than with secondary hydroxyls (Ionescu, 2005). It is estimated that the reactivity of secondary hydroxyls is only about one-third that of primary hydroxyls (Herington and Hock, 1997). Furthermore, attaching hydroxyl groups to castor oil especially on primary carbon atoms not only increases the hydroxyl functionality of the oil, but also enhances its thermal stability (Liu et al., 2014). Consequently, PUs from polyols with primary hydroxyls are more stable than those with secondary hydroxyls (Tassie, 2014). Castor oil is therefore chemically modified to raise its hydroxyl functionality and reactivity, and to enhance its structure and physical properties. Among various methods employed by researchers for the chemical modification of castor oil to generate polyols, the most widely used procedures are:
(i) Epoxidation of the oil, followed by oxirane ring opening and subsequent hydroxylation (Sinadinovic-Fiser et al., 2012).
(ii) Transesterification of the oil using polyhydroxy compounds such as ethanolamine, glycerol, pentaerythritol etc, in presence of acid/base catalyst (Mosiewicki et al., 2009; Islam et al., 2014).
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1.4 Glycerolysis of Castor Oil
Scheme 1 depicts the high-temperature, PbO-catalysed glycerolysis of castor oil, resulting in the splitting of the triglyceride molecule in the oil to yield polyol fractions bearing additional hydroxyl group(s) (Kimmel, 2004), but with lower average molecular weight compared to castor oil itself.
However, partial glycerolysis of castor oil yields a mixture of mono- and diglycerides (Equation 1), with some free hydroxyl groups in the reaction mixture.
1.5 Polyurethanes (PUs)
Polyurethanes are polymers containing the urethane or carbamate linkage (-NHCO-O-) as repeat unit in their molecular backbones. It was the pioneering work of Dr. Otto Bayer and his co-workers that not only produced the first PUs in 1937 (work actually published in 1947), but also provided the fundamental chemistry for the PU industry. Later, the first PU elastomers were produced in 1940 as a World War II programme to develop viable alternatives to rubber. Production of flexible PUs only came on stream
……(1)
……….(2)
Scheme 1: Glycerolysis of castor oil
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in 1954. In 1967, urethane modified polyisocyanurate rigid foams were introduced to offer better thermal stability and flammability resistance.
PUs generally are chemically diverse materials with corresponding diverse physical and chemical properties. As a result, PUs can be tailored to meet diversified demands of various applications such as coatings, adhesives, fibres, thermoplastic elastomers and foams. However, the advent of bio-based PUs was the result of increasing costs of petrochemicals, as well as rising and sustained environmental concerns on the negative impacts of petroleum-based polymers.
1.6 Chemistry of PU Synthesis
Polyol and organic polyisocyanate are the most important raw materials in PU synthesis, and the two react (in presence of blowing agents, catalysts and surfactant) according to the generalised PU reaction
R (OH)n + R1-(N=C=O)n R – ( NH.CO-O)n-R1 (3)
polyol polyisocyanate polyurethane
(where n > 2)
to produce linear product. Isocyanate functionality is the foundation of PU chemistry. The reactivity of the isocyanate group towards active-hydrogen compounds is largely due to the ability of this group to form resonance structures (below).
-N-C=O -N=C=O -N=C-O (4)
+
–
+
–
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O
O
O
O
Attack of nucleophilic centres on the electrophilic carbon atom by active-hydrogen compounds (electron donors) is responsible for initiating chemical reaction between the two species (Sykes, 1999) to produce activated complex as intermediate.
However, other reactions also take place if there is a stoichiometric excess of isocyanate in the formulation. This excess is needed to carry through all the primary and secondary PU reactions leading up to the formation of multifunctional allophanate and biuret moieties (Scheme 2).
Primary reactions
RNCO + R’OH RNHCOOR’ (bifunctional) (5)
urethane group
RNCO + H2O RNHCOOH (6)
Carbamic acid
RNHCOOH RNH2 + CO2 (7)
RNCO + R’NH2 RNHCONHR’ (bifunctional) (8)
substituted urea
Secondary reactions
RNCO + ─ NH – C – O ─ ─ N – C – O ─ (trifunctional) (9)
CONHR
allophanate
RNCO + ─ NH – C – NH─ ─ N – C – NH ─ (trifunctional) (10)
CONHR
biuret
The latter are associated with crosslinking and chain branching reactions that often result in network formation and foam rigidity (Luo et al., 2008; Kim et al., 2008).
Consequently, most PU products obtained from vegetable oil polyols have been found to be crosslinked materials or thermosets (Guo et al., 2000; Zlatanic et al., 2002; Petrovic et al., 2005).
Scheme 2: Primary and secondary reactions during PU foam synthesis.
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The association of three isocyanate groups into cyclic trimer units (isocyanurates) that are capable of chain branching and crosslinking is another possibility (Wirpsza, 1993) (Fig. 1.4).
Fig. 1.4: Structure of isocyanurate trimer
This also leads to network formation to yield rigid polyisocyanurates (Del Rio, 2011), the latter more heavily crosslinked than rigid polyurethanes. In other words, two types of rigid foams are derivable from this system – rigid polyurethanes and rigid polyisocyanurates.
1.7 Polyurethane Foams (PUFs)
PUFs are cellular plastics with versatile applications in thermal insulation, packaging, cushioning and floor covering (Brydson, 1999). Rigid PUFs are used as structural and engineering materials especially in construction, thermal insulation, buoyancy and refrigeration, while flexible PUFs are mainly used as cushioning, seating and packaging materials (Woods, 1990). Use of rigid foams is as a result of their low heat conduction coefficient (very low heat transfer), low water absorption and relatively good mechanical strength (Randall and Lee, 2002). However, any foamed material is a good insulator by virtue of the low conductivity of the gas (air) contained in the system.
Polyurethane foams differ from unfoamed polyurethanes in that their production requires the incorporation of a gas that will expand or blow the polymer into a foam.
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This confers on the former greater impact absorption capacity than the latter. The basic principle of foaming is the dispersion of the gas phase in a liquid to obtain a liquid foam which later solidifies into solid cellular product in contact with air. The reaction between isocyanate group and water generates amine and carbon dioxide gas, the latter starting or initiating a blowing process that is aided by heat generated due to the exothermic nature of the reaction, and thus giving the foam its cellular structure. The density of foam largely depends on the amount of carbon dioxide gas produced (Bhatnagar, 1992). The amine reacts with other diisocyanates, resulting in urea-linkages in the foam. The polyol (soft) phase, on reacting with isocyanate groups, covalently bonds with urea hard segments through urethane linkages (Aneja, 2002).
PU foams are cellular structured polyurethanes consisting of a network of spherical, quasi-spherical, octahedral or pentagonal dodecahedral cells which behave as micro-springs (Herrington and Hock, 1998). Each cell may be completely enclosed by a membrane (impermeable) or it may be inter-connected with its neighbours (permeable or porous). By nature of cells, two main types of foams exist namely, rigid and flexible foams (Fig.1.5).
* Open cell, low density foam
+ Closed cell, high density foam
Fig.1.5: Types of polyurethane (PU) foams
PU Foam
Flexible * ⃰⃰*
Rigid +
Semi-rigid
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However, by appropriate selection of reactants and controlling conditions for the foaming process, it is possible to produce rigid, semi-rigid or flexible foams (Bhatnagar, 2004). The semi-rigid foams may be used in specialty applications where some load bearing and impact resistance properties are required at the same time (Northstar Polymers, 2000- 2007).
1.7.1 Cell structure
The presence or absence of windows in the cells or the number of windows per cell, which constitutes the cell structure, is a function of the process by which the foam is made. Rigid foams are high density, closed-cell foams. The closed cells (spherical) are small, tightly walled individual cells, that do not allow air or liquid permeability, and in which heat transfer is very low. This makes rigid foams good thermal insulators, with a high degree of buoyancy (Sivertsen, 2007). Flexible foams on the other hand are low density, open cell foams. They are made up of larger, loosely or incompletely walled inter-connected cells that are porous. Such cells will act as a sponge, sucking up liquid by capillary action (Aneja, 2002). Cellular morphologies of PU foams can be captured and probed using various microscopic techniques that include optical microscopy (OM), scanning electron microscopy (SEM), small angle x-ray scattering (SAXS), atomic force microscopy (AFM) etc. (Tyagi et al., 1986; Kaushiva et al., 2000; Aneja and Wilkes, 2002).
1.8 Castor Oil-Based PUFs (COPUFs)
PUFs produced from castor oil polyols are known to have some excellent chemical and physical properties such as enhanced hydrolytic and thermal stability due largely to the
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hydrophobic nature of their triglycerides (Zlatanic et al., 2002; CastorOil.in, 2015), in addition to their environment-friendly nature. However, most PU products obtained from vegetable oil polyols (including castor oil polyols) have been found to be crosslinked materials or thermosets (Guo et al., 2000; Zlatanic et al., 2002; Petrovic et al., 2005). This has constituted a serious problem especially with regards to the production of soft, flexible PUFs that are widely used both in industry and daily life as cushioning, packaging and adhesive materials. In order to obtain soft, flexible PUFs based on renewable castor oil polyol, many researchers resorted to blending conventional petroleum-based polyether polyols with varying proportions of castor oil as replacement of the base polyol (Ogunniyi et al., 1998; Xu et al., 2008; Zhang, 2008; Chan, 2008; Xing, 2014). Although cost-benefit analysis of blending polyether polyol and castor oil has indicated some level of cost effectiveness (Ogunfeyitimi et al., 2012; Thorat and Patil, 2015), these mixed polyol recipes were not quite successful, as the castor oil proportion needed to produce soft, flexible foams was no more than 20 – 25% (Ogunniyi et al., 1998; Ogunfeyitimi et al., 2012; Dalen et al., 2014). Moreover, in such mixed polyol formulations, the compatibility question between castor oil and conventional polyether polyol is a very important one. Current challenges therefore are on how to make or produce soft, flexible PU foams from 100% castor oil content as polyol component in foam formulation. This could lead to substantial reduction in production cost and the maximal exploitation of castor oil as raw material for flexible PUF production. Consistent with this, the present work has sought to produce soft, flexible castor oil-based PUFs by the use of two moderately long, straight-chain chlorinated paraffins (CPs ) (formulae C14H23Cl7 and C17H29Cl7) as internal liquid plasticizers introduced in-situ in castor oil polyol component of foam formulation during foam synthesis. These CPs, whose physico-chemical properties depend largely
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on their chain length and chlorine content (Houghton, 2003), are compatible with oils generally, and are reported to have advantage over conventional plasticisers by both increasing the flexibility of a material, as well as enhancing its fire retardancy and low temperature strength (Klorfin, 2012). Details on this novel application are discussed in later chapters of this work.
1.9 Polymer Foam Formulations
In foam making, the desired end-properties of the foam dictate the choice of specific components along with their required quantities (Aneja, 2002). Major components needed to synthesise PU foam are diisocyanate, polyol, water, physical blowing agents, catalysts, surfactants and cross-linking agents. However, the most important components are polyol and diisocyanate. Hence their unique functionalities, polarities and symmetries must be considered in working out foam making recipes. PU formulations can be tailored and/or controlled to produce a wide range of materials with varied properties and end-uses. The materials include:
(i) Low density flexible foam
(ii) High density rigid foam
(iii) Soft solid elastomers
(iv) Hard solid plastics
(v) Coatings, adhesives, fibres and sealants.
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Stiffness and elastic behavior of foam, for instance, can be adjusted by controlling the hard segment (HS) to soft segment (SS) ratio in the formulation (Aneja, 2002).
In PU foam formulations, two types of diisocyanates (both aromatic) are used namely, toluene diisocyanate (TDI) and methylene diphenyl isocyanate (MDI). The diisocyanate is a mixture of two isomers which differ slightly in reaction rate.
The major advantage of the aromatic diisocyanates in PU systems is that they react faster, while their aliphatic counterparts are more UV-stable, and do not undergo yellowing on exposure to light (Sykes, 1999). Isocyanates constitute the hard segment of foamed PUs. Isocyanate added to the formulation is usually reported by an index number. An isocyanate index of 100 indicates that there is a stoichiometric amount of isocyanate added to react with functional groups from the polyol, water and cross-linkers in the formulation. Polyols on the other hand, constitute the soft phase or soft segment of PU foam. Two kinds of polyols commercially available for PU foam production are the polyesters and polyethers. However, almost 90% of the PU foam market utilises polyether polyols based on polypropylene oxide in comparison to
Fig.1.6: 4,4‟-Diphenylmethane diisocyanate (MDI)
Fig.1.7: 2,4- and 2,6-Toluene diisocyanate (TDI)
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polyester polyol. Advantages of the polyether polyols include low cost, better hydrolysis resistance, better resilience and better ease of handling (Aneja, 2002).
Polyols used in flexible foam formulation are higher molecular weight compounds (3000-6000gmol-1) compounds, with average functionalities of 2.5-3.0 (Herrington and Hock, 1998). Flexible foams are formed by a process of simultaneous polymerisation and expansion. The gas for expansion is primarily carbon dioxide produced by the reaction of isocyanate and water. The reaction with water also produces substituted urea cross-links, which stabilizes the expanding foam. To prevent serious foam shrinkage, the cells must be open to allow air to penetrate. Rigid urethane foams, however, are made from more highly branched lower molecular weight polyols with functionalities as high as 8.0 (Aneja, 2002). The increased branching and shorter aliphatic chains contribute to more rigid molecular structures. Because of the lower hydroxyl equivalent weight of the polyol, a higher concentration of aromatic polyisocyanate is needed to obtain the same equivalent ratio. Rigidity of PU is closely associated with the formation of cross-linked structures and urea linkages (Luo et al., 2008; Kim et al., 2008; Ogunniyi et al., 1998).
The basis for the formulation of rigid PU foams is the same as that used for flexible foams, with the exception that rigid foams are highly cross-linked structures. This would imply among others, greater isocyanate/polyol (NCO/OH) ratio, i.e. stoichiometric excess of isocyanate, less amount of water and use of a polyol with hydroxyl functionality not less than 3 in foam formulation. Isocyanate and polyol are the most basic ingredients. An organotin compound catalyses the reaction, especially in the presence of small amount of tertiary amine. Silicone surfactant regulates the cell size uniformity and also controls the viscosity and surface tension of the cell membranes as they are stretched during foaming. Physical blowing agent is also
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introduced and this increases the total volume without itself participating in the chemical reactions that are occurring. Water is not an essential ingredient. Table 1.2 represents formulation basics for flexible PU foams, while Table 1.3 gives a recipe for rigid polyurethane foam synthesis.
Table 1.2: Formulation basics for flexible polyurethane foams (Herrington and Hock, 1998).
Component
Parts by weight
Polyol
100
Inorganic Fillers
0 -150
Water
1.5 – 7.5
Silicone Copolymer Surfactant
0.5 – 2.5
Amine Catalyst
0.1-1.0
Tin Catalyst
0.0- 0.5
Chain-Extender
0 – 10
Cross-Linker
0 – 5
Additive
Variable
Auxiliary Blowing Agent
0 – 35
Diisocyanate
25- 85
Table 1.3: Typical formulation for rigid polyurethane foam synthesis (Chanda and Roy, 2006).
Component
Parts by weight
Polyol (f ≥3)
100
Catalyst 1 (N,N-cyclohexylamine)
0.3
Catalyst 2 (N,N-dimethylethanolamine)
0.3
Freon II (CFCl3)
50
Water
1
Surfactant (block copolymer of polyether and silicone)
1
4,4-diphenylmethane diisocyanate (MDI)
100
(index = 100)
Two reactions (blow and gelation) go on simultaneously in the foaming process. Hence catalysts are chosen for each reaction such that there is balancing of the reactions to avoid collapsing of product, and ensuring expansion of the foam structure. Also, uniform mixing of reactants is necessary to produce a homogeneous foam. It has been
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observed that adequate, uniform mixing enhances both the gas blowing and cross-linking reactions, while improper mixing results in foams with relatively big cell size and low resilience (Adogbo and Atiwurcha, 2014). Because foaming reaction takes place very rapidly, large scale production of foam demands automatic mixing equipment.
1.10 Structure-Property Relationship in Polymers
Natural and synthetic polymers are known to exhibit wide diversity of properties. Some are rigid, hard, strong and dimensionally stable, while others appear soft, flexible or largely extensible under the influence of stress. Some show ready solubility and fusibility, while others appear more resistant to heat and solvents. In many biological macromolecules such as polynucleic acids (e.g. ribonucleic acid, RNA, and deoxyribonucleic acid, DNA), proteins, celluloses, lipids etc, structure-property relationships are strongly influenced by hydrogen bonding and crystallisation (Jeffrey and Saenger, 1994; Alper, 2002; Vogel, 2002). However, synthetic polymers are produced on an industrial scale primarily for use as structural materials. Their physical properties are particularly important in determining their usefulness, be they rubbers, plastics or fibres. According to Ghosh (2006), factors that influence polymer properties in general are: molar cohesion, polarity, molecular weight, crystallinity, overall molecular symmetry (both recurrence symmetry and architectural symmetry), linearity and non-linearity of chain molecules. Higher molecular weight permits greater degree of chain entanglements, thus resulting in higher melting temperature (TM) and tensile strength (TS). Branching will make the polymer less resistant to solvents, chemicals and heat owing to increased mobility manifested through the branch units or pendant
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groups. But high degrees of branching with enhanced branch lengths and ultimate crosslinking render the polymer relatively stiff, arising from greater degrees of chain entanglement and leading to the formation of giant molecules with a network structure. This restrains large scale molecular mobility or chain slippage, thus improving dimensional stability and resistances to thermal and mechanical loading.
Crosslinking causes basic structural changes in polymers, with attendant changes in polymer properties. Crosslinks are very important in determining physical properties because they increase molecular weight and limit translational motions of polymer chains with respect to one another. Presence of a few crosslinks is enough to greatly reduce solubility of a polymer and produce a gel polymer (Ghosh, 2006). Thus, the tendency to absorb solvents decreases as the degree of crosslinking is increased because the chains cannot move enough to allow the solvent molecules to penetrate between the chains. But polymers that are not highly crosslinked have properties that depend greatly on the forces that act between the chains.
1.11 Effect of Filler Incorporation on Morphology and Structure of PUFs
The use of reinforcing fillers in PU foam formulations produces composite materials with modified morphology and structure, and enhanced performance (Lees, 2013). However, satisfactory performance of such composites depends to a large extent on the degree of dispersion of the reinforcing filler in the polymer matrix, and strong interfacial filler-matrix interaction and adhesion. In PU foams, mechanical properties are primarily controlled by the cellular structure of the PU, as well as the nature of chemicals that constitute the hard and soft segment phases in the foam structure. In flexible PU foams, fillers fill voids in the open-cell porous structure of the polymer
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matrix, to promote among others an increase in density and resistance to compression, with attendant improvement in mechanical strength (Latinwo et al., 2010). They however reduce resilience, and contribute to an increase in permanent deformation (Usman et al., 2012). Many studies have shown that modification in the properties of flexible PU foams is achieved by the dispersion of the filler particles across the polymer matrix along with polyurea hard segments. In this way, shape, size and mobility of hard domains, mobility of soft segments, load bearing characteristics and overall flexibility and modulus of the polymer matrix can be affected (Agarry et al., 2015). This means that compatibility between the reinforcing filler and the polymer matrix is a very important issue.
Reinforcing fillers used in flexible PU foam formulations include inorganic fillers (e.g. calcium carbonate, dolomite, aluminium silica, talc etc) and organic materials (carbon black, natural fibres such as wood and non-wood fibres) (Mothe and Araujo, 2000; Mothe et al., 2002). However, calcium carbonate and glass fibre are the most commonly used (Lees, 2013). Calcium carbonate (whether micro- or macro-sized) is known to improve significantly, load-bearing properties and modulus characteristics of PUs (Nunes et al., 2000; Chen et al., 2002; Latinwo et al., 2010); while glass generally confers high strength and high modulus to the reinforced polymer (John, 2001). The need for filler reinforced plastic composites generally arises because conventional materials cannot meet many desired property requirements of modern technology. Hence the use of metallic/mineral particles as well as glass or fibre to achieve material property requirement in plastics and other engineering materials is a well known practice (Cotgreave and Shortall, 1977; Javni et al., 2011).1.12 Flammability Characteristics of PUFs
Polymer foams are very flammable on account of their high hydrocarbon content as organic polymers, as well as their predominantly cellular structure (Wilde, 1980). The latter allows for a lot of air permeability within the foam matrix. With regard to air permeability, flexible or open cell foams are less dense and more porous than rigid foams, and therefore more flammable (Sivertsen, 2007). Ease of ignitability and high combustibility tend to limit the application of foamed polymers as mattresses, cushioning and seating materials, packaging materials, insulators in building and construction etc. The flammability of PUFs is therefore an important industrial issue.
A major challenge in the use of PUFs both in domestic and industrial applications is how to reduce the flammability of these materials to enhance their safety of application. Flame retardants (FRs) are chemicals used to lower the ignitability and combustibility of polymers, thereby reducing the risk associated with incident fires that have become regular occurrences in everyday life (Eboatu et al., 1995).
From literature, FR chemicals usually incorporated into PUFs to reduce their flammability include phosphorus-containing compounds, halogen-containing compounds, nitrogen-containing additives, silicone-containing products etc. (Pearce, 1986; Weil and Levchik, 2004; Singh and Jain, 2008; Papazoglou, 1994; Jurs, 2004; Wang et al., 2012). Halogen-containing FRs in particular have been used either singly or as mixtures with synergists like Sb4O6, Fe2O3, ZnO etc. (Lyons, 1970; Kurt and Reegen, 1975). However, a major disadvantage of some halogenated FRs in PU foams is that they are not only potential toxicants at moderately low to high temperatures, but that they are also susceptible to hydrolysis (Singh and Jain, 2008).
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The thermal degradation of PU foams and its relation to foam ignition have been studied with a variety of analytical and existing fire-test methods (Tang et al., 2002; Hager et al., 2004; Lefebvre et al., 2004). Among major parameters studied in these systems are ignition time, flame propagation rate, after-glow time, heat release rate, mass loss rate, smoke density etc. The thermal stability and ignition of conventional PU foam depends on the composition (Lefebvre et al., 2005). When PU foam is subjected to heat, various PU linkages are broken at different temperatures (Singh and Jain, 2008). The dissociation of PU foam linkages at different temperatures is shown in Table 1.4.
Table 1.4: Dissociation of Polyurethane Foam Linkages at Different Temperatures (Singh and Jain, 2008).
Linkage
Dissociation temperature (0C)
Allophanate
100–120
Biuret
115–125
Urea
160–200
Urethane
180–200
Disubstituted urea
235–250
Carbodiimide
250–280
Isocyanurate
270–300
Halogen-containing FRs, for instance, have been reported as acting chemically by radical quenching in the vapour phase to interfere at particular stages of the polymer combustion process (Dufton, 2003; Weil and Levchik, 2009; Laoutid et al., 2009).
Flammability testing is essentially an assessment of how easily a material will ignite or burn, causing fire or combustion. In this study, flammability testing of castor oil-based PUFs will be carried out as an assessment of material fire safety and a basis for its enhancement, given the immense domestic and industrial application of these foams.
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1.13 Mechanical Properties of Polymer Foams
The mechanical properties of a polymer are those properties that are manifested when the polymer is subjected to mechanical stresses, and they collectively determine the applicability or end use of the polymer. The response of a polymer to mechanical stresses will depend upon its gross morphology and the behaviour of its molecules. Size or molecular weight, flexibility/rigidity and intermolecular interactions are very important characteristics that can influence mechanical properties generally (Meijer and Govaert, 2005). According to Alexandre and Dubois (2000), mechanical properties of polymeric materials are largely determined by their molecular structure, morphology and processing methods. Mechanical properties of foams differ from those of un-foamed solid polymers. The former generally have greater impact-absorption capacity than the latter. Flexible foams compress more than rigid foams because in an open-cell structure, the gas phase is not held together. Since gas has the least mechanical strength, open cell (flexible) foams have lower Young‟s modulus, compressive and tensile strengths (Sivertsen, 2007). Moreover, since these mechanical properties are substantially anisotropic because the strength of foam is always better along the direction of foaming, geometry of foams could have more to say for the strength than density, chemistry and the amount of open cells in the structure (Chan and Nakamura, 1969).
1.14 Polymer Foam Geometry
In the making of polymer foam, mixed starting materials react, expand and flow, increasing in molecular weight and viscosity and eventually forming cross-linked structures after curing. But on a microscopic scale, cells nucleate, grow in size, coalesce, stabilise and open in case of flexible foam. In polymer foam, it is not only
27
polymer molecules in the polymer matrix that determine the properties of the foam, but also the gas-filled space between them. Intercellular gas interacts with the polymer matrix, affecting its properties and behaviours over time (Sivertson, 2007). Specifically, the properties of foamed polyurethanes will depend on:
(i) The chemical composition and thickness of the cell walls.
(ii) The volume-solid matter/air ratio.
(iii) The concentration of the cell membranes (air permeability/ open cell structure).
Size and shape of cells or pores in polymer foam are very disperse, since the packing of spherical cells in a foam are never regular. Consequently, adequate description of foam structure would require detailed statistical procedures (Sivertson, 2007).
1.15 Research Objectives of the Study
Aim or main objective of the study was to investigate the structure-property relationships of castor oil-based polyurethane foams (COPUFs).
The specific objectives of the study were to:
(i) Extract/prepare castor oil and castor oil polyols (COPs) for polyurethane foam production.
(ii) Produce COPUFs using different formulations.
(iii) Characterise the process parameters (cream time, free-rise time, gel time, tack-free time, and foam rise), physico-mechanical properties (density, water absorption, compressive strength, and creep recovery), flammability properties (IT, FPR, AGT) and morphology of the COPUFs.
(iv) Relate the structure of the COPUFs to their properties.
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Fig. 1.8: Flow chart of CO utilisation potential in COPUF synthesis during the study.
1.16 Statement of Research Problem
Polyol and organic isocyanate are the major raw material ingredients in the production of polyurethane foams (PUFs). Petroleum-based polyols are not only environmentally unsafe, but are very expensive; and this is costing Nigeria a lot of foreign exchange, as foam-making industries in the country are still stitched in mass importation of petro-polyols. Bio-based polyols derived from vegetable oils are renewable and environment friendly, and could be used as replacement for the petro-polyols. However, these natural oil polyols (NOPs) are known to produce mainly rigid/
Key
* By glycerolysis/PCl5-chlorination
+ No practical value
Filled COPUF
(semi-rigid to rigid)
NCOP
Test and analysis
Test and analysis
Test and analysis
Flexible/semi-flexible COPUF
Test and analysis
Control COPUF
(semi-rigid)
Fire-resistant COPUF
NCOP
GMCOPs/PMCOPs
GMFs/ PMFs +
(rigid) (brittle)
Test and analysis
Castor seeds
(R. communis Linn)
Mechanical expression
(<450C)
Virgin CO
Purification
(Fine mesh screen)
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semi-rigid PUFs (Guo et al., 2000; Zlatanic et al., 2002). A major challenge, therefore, is to produce soft, flexible PUFs (from bio-based polyols) with physico-mechanical properties (density, water absorption, compressive strength etc) within prescribed standards for the conventional flexible PUF. Another challenge is how to optimally impart fire retardancy characteristics on the PUFs to enhance their ability to suppress or mitigate incident fires during use. This work has sought to address both challenges using 100% castor oil or its modified polyols as polyol component.
1.17 Justification/Significance of the Study
This study is premised on the need to continue to provide, through research, additional perspectives and insight into the possibility of replacing expensive and environmentally unsafe petroleum-based raw materials for the chemical industry, with renewable, biodegradable and non-toxic bioresources of plant origin, on a sustainable basis. Castor oil, a vastly available, cheap, non-edible vegetable oil that is locally sourced in Nigeria, could replace conventional polyols in the industrial production of PU foams (Ogunniyi, 2006; Ogunfeyitimi et al., 2012). If actualised, this has the potential of saving a lot of foreign exchange for the country. As highlighted earlier in this work, castor oil has numerous advantages over other vegetable oils, chief among which are its being hydroxylated , its high thermal stability and its hydrophobicity/hydrolytic stability as a result of a long (C18) fatty acid chain structure.
Globally, there has been a growing research interest in this area. However, to date, there has been only limited research on castor oil-based PU foams in Nigeria. More research work is imperative therefore, to further explore this potential in the country.
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1.17 1.18 Contributions to Knowledge
(i) The study utilised modified castor oil polyol to produce castor oil-based polyurethane foams.
(ii) The castor oil and modified castor oil were characterised by titrimetric, FTIR, GC-MS and some physico-chemical characteristics (parameters).
(iii) The structure-property relationships of castor oil-based polyurethane foams were established through process; physico-chemical, mechanical, morphological and flammability parameters.
(iv) Additives improved the density, compressive strength and fire retardancy characteristics of the polyurethane foams.
(v) The study demonstrated that the use of CaCO3 filler and fire retardants enhanced the fire retardancy characteristics of the polyurethane foams.
1.19 Scope/Limitations of the Study
In order to fulfill the above stated objectives, the scope of study will cover the following :
(1) Extraction of castor oil from wild Ricinus communis Linn seeds.
(2) Chemical modification of purified castor oil by
(i) transesterification/alcoholysis using glycerol (glycerolysis);
(ii) sulphation using concentrated H2SO4;
(iii) chlorination using PCl5 .
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(3) Characterisation of the pure and modified castor oil in terms of specific gravity, viscosity, refractive index, as well as hydroxyl, saponification, acid and iodine numbers.
(4) FTIR and GC-MS analysis of the modified oils to establish modification of oil structure.
(5) Preparation of PU foams of different formulations from the neat and modified castor oil.
(6) Density and water absorption measurements of foams.
(7) Mechanical property testing, e.g. compressive strength, creep recovery etc of the produced PU foams using standard methods.
(8) Analysis of the cellular morphologies of the foams using SEM.
(9) Studying the effects of chemical modification on morphology and mechanical properties of the PU foams.
(10) Investigating how the use of reinforcing fillers in the PU matrix would affect morphology, mechanical properties and flammability characteristics of the PU foams.
(11) Studying the flammability of the PU foams generally, and the effect of incorporating fire retardants in the PU matrix.
Limitations/constraints encountered during the study included:
(i) Inability to access functional Cone Calorimeter and DSC instruments. The former would have been used for detailed study of the flame properties of the foams, while the latter could have been used to monitor the glass transition temperatures of filled, plasticised and crosslinked COPUFs.
(ii) Shortage of funds.

 

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