ABSTRACT
The effects of fabric architectures and alkali treatment on the properties of cotton fabric- reinforced unsaturated polyester composites have been studied. The problems of low mechanical properties of textile composites from natural origin have been a source of concern for researchers; insufficient utilization of cotton fibres has further reduced the economic returns of cotton growers. In this work, four different yarns of known count were twisted (plied) to obtain a single strand which was woven and knitted into fabrics of different architectures. The cotton fabrics were subjected to chemical modifications using 20% sodium hydroxide for 1 and 2 minutes and its influence on some mechanical properties were analyzed. The fabrics were used to reinforce unsaturated polyester resin as matrix, applying both single layer and two layers of fabrics to form different 2-ply laminate configurations. The tensile and flexural strength, tensile and flexural modulus, impact strength and hardness of the textile composites were compared. Alkali treatment improved the tensile strength and breaking extension of the fabrics by 10-30% and 31-56% respectively requiring a certain percentage concentration and duration of treatment, going by the fact that the close treatment times of 1 and 2 minutes with 20% concentration of sodium hydroxide gave inconsistent tensile strength and breaking extension. Fabric architecture was found to have great influence on the breaking strength of the fabrics. The tensile strength of the fabrics was found to decrease in this order: Plain woven fabric > twill fabric > knitted fabric when untreated, but when treated, twill fabric > plain fabric > knitted fabric. Composites reinforced with twill fabrics generally had better tensile strength and modulus as well as flexural strength and modulus than those reinforced with plain and knitted fabrics either when the reinforcing fabrics were untreated or treated with sodium
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hydroxide with an increase of 72–119%. The flexural strength of composite with twill, plain and knitted fabrics are 62.32%, 56.75% and 52.68% respectively and increased by 65%, 60% and 37% when treated with 20% NaOH. Results also showed that increase in the volume of reinforcement (increase in fabric layer) gave a corresponding increase in the mechanical properties of the composites; however, the increase was not proportional with respect to those composites reinforced with single fabric samples. The mechanical properties tested were optimized by the plying effect carried out on the yarns. The impact strength of the unsaturated polyester was improved by about 105% when reinforced with the fabrics. Composites reinforced with knitted fabrics showed better resistance to impact forces than other fabrics with good energy absorbing characteristics. There was an increase in the Rockwell hardness of polyester resin composite for both single and double layer reinforced laminates. Composites with twill fabrics gave highest hardness number (25.9) than those of other fabrics (plain, 24.4 and knitted, 22.2) for the single ply and same for 2-ply (twill-twill, 30.6; plain-plain, 29.9 and knitted-knitted, 25.6). Much variation in hardness numbers were not recorded for the various reinforcements. The behaviour of other hybrid composites reinforced with two layers of fabrics was seen to follow the properties of the fabrics reinforcing them.
Keywords: Cotton fabrics, Composites, Unsaturated polyester resin, Weaving, Mechanical properties
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TABLE OF CONTENTS
Title Page……………………………………………………………………………………………………………..i
Declaration…………………………………………………………………………………………………………..ii
Certification…………………………………………………………………………………………………………iii
Acknowledgement………………………………………………………………………………………………..iv
Abstract……………………………………………………………………………………………………………….v
Table of Contents…………………………………………………………………………………………………vii
List of Figures………………………………………………………………………………………………………xi
List of Tables………………………………………………………………………………………………………xiii
List of Plates……………………………………………………………………………………………………….xv
List of Appendices………………………………………………………………………………………………xvi
Abbreviations……………………………………………………………………………………………………..xvii
CHAPTER ONE
1.0 INTRODUCTION……………………………………………………………………………………..1
1.1 Statement of Research Problems…………………………………………………………………3
1.2 Research Aims and Objectives…………………………………………………………………….3
1.3 Justification……………………………………………………………………………………………….4
1.4 Scope of Research Study…………………………………………………………………………….5
CHAPTER TWO
2.0 LITERATURE REVIEW…………………………………………………………………………..6
2.1 Composites…………………………………………………………………………………………………6
2.2 Constituents of Composites…………………………………………………………………………6
2.2.1 Matrices………………………………………………………………………………………………………6
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2.2.2 Reinforcement…………………………………………………………………………………………….13
2.3 Natural fibre reinforced polymer composites………………………………………………14
2.4 Effects of Processing Temperature on cellulose composites………………………….15
2.5 Chemical compositions of Natural fibres…………………………………………………….16
2.6 Cotton fibre……………………………………………………………………………………………….16
2.7 Advantages and Disadvantages of Natural fibres………………………………………..18
2.8 Fibre modification……………………………………………………………………………………..20
2.8.1 Physical methods of modification………………………………………………………………….20
2.8.2 Chemical methods of modification………………………………………………………………..21
2.9 Fibre/Yarn Architecture…………………………………………………………………………….28
2.9.1 Fibre configuration or Architecture………………………………………………………………..28
2.10 Textile Composites……………………………………………………………………………………..30
2.11 Typical Textile Composites…………………………………………………………………………31
2.11.1 Woven fabrics…………………………………………………………………………………………….32
2.11.2 Braided fabrics……………………………………………………………………………………………36
2.11.3 Knitted fabrics……………………………………………………………………………………………38
2.12 Mechanical properties of Textile Composites based on natural fibres………….40
CHAPTER THREE
3.0 MATERIALS AND METHOD…………………………………………………………………42
3.1 Experimental…………………………………………………………………………………………….42
3.2 Materials…………………………………………………………………………………………………..42
3.2.1 Chemicals and Reagents……………………………………………………………………………..42
3.2.2 Materials……………………………………………………………………………………………………43
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3.2.3 Equipment/Machines…………………………………………………………………………………..44
3.3 Methods……………………………………………………………………………………………………44
3.3.1 Fabric Production……………………………………………………………………………………….44
3.3.2 Fabric Surface Treatment…………………………………………………………………………….44
3.3.3 Tensile properties of the yarn and fabrics………………………………………………………44
3.3.4 Mould fabrication……………………………………………………………………………………….45
3.3.5 Preparation of Composites…………………………………………………………………………..46
3.3.6 Cutting of Composite samples……………………………………………………………………..48
3.4 Testing and Characterization…………………………………………………………………….49
3.4.1 Tensile and Flexural Testing of composites……………………………………………………48
3.4.2 Impact strength testing………………………………………………………………………………..51
3.4.3 Rockwell Hardness test……………………………………………………………………………….52
CHAPTER FOUR
4.0 RESULTS AND DISCUSSION………………………………………………………………..53
4.1 Fabric Production…………………………………………………………………………………….53
4.1.1 Yarn and fabric parameters………………………………………………………………………….54
4.2 Fabric Surface treatment…………………………………………………………………………..54
4.3 Tensile Properties of the Yarn and fabrics …………………………………………………55
4.4 Breaking Extension of yarn and fabrics……………………………………………………..58
4.5 Tensile and flexural testing of composites…………………………………………………..59
4.5.1 Tensile strength and Modulus of Composite samples………………………………………60
4.5.2 Flexural properties of cotton/unsaturated polyester composite………………………….65
4.6 Charpy Impact strength testing………………………………………………………………….72
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4.6.1 Impact strength of composites reinforced with single layer of fabric…………………72
4.6.2 Impact strength of composites reinforced with two layers of fabrics …………………74
4.7 Rockwell Hardness Test…………………………………………………………………………….76
4.7.1 Hardness of composites reinforced with single layer of fabric………………………….77
4.7.2 Hardness of composites reinforced with two layers of fabric ……………………………77
CHAPTER FIVE
5.0 SUMMARY, CONCLUSION AND RECOMMENDATIONS……………………80
5.1 Summary…………………………………………………………………………………………………..80
5.2 Conclusion………………………………………………………………………………………………..83
5.3 Recommendations…………………………………………………………………………………….86
REFERENCES…………………………………………………………………………………………………..88
APPENDICES…………………………………………………………………………………………………….114
CHAPTER ONE
1.0 INTRODUCTION
Due to the ever increasing global interest on new structural materials from natural sources, efforts are on to reduce the cost in raw materials, manufacture and maintenance of composites. With a view to replacing the wooden fittings, fixtures and furniture, natural composites reinforced with jute, kenaf, sisal, coir, cotton, straw, hemp, banana, pineapple, coconut, rice husk, bamboo etc. can be used instead of the conventional polymer composites reinforced with man-made fibres such as glass, carbon, aramid etc. Until recently, there has been only limited information available towards understanding the behaviour of composites reinforced with natural fibres.
The development of textile composites has been mainly the investigation of textile fabrication techniques and evaluation of the mechanical properties. Researches on textile technologies such as weaving, knitting and braiding has resulted in the formation of textile composites that have higher mechanical properties, as continuous orientation of fibres is not restricted at any point (Yan, et. al., 2002).
The increased interest in textile reinforcements is due to the enhanced strength, lower production cost and improved mechanical properties, which they offer, compared to their non-woven counterparts. Another special feature of textile reinforcement is the interconnectivity between adjacent fibres. This interconnectivity offers additional interface strength to improve the relatively weak fibre-resin interface. In addition, woven and knitted fabric composites may be more damage tolerant in the case of a delamination.
There has been report on the increase of lateral cohesion of filament for twisted yarns as well as improved ease of handling (Naik and Kuchibhotla, 2002). In fact, fibre twist is found to induce normal forces between fibres and this increasing inter-fibre friction
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gives yarn cohesion. However, by twisting yarns, there is the possibility of micro damages within the yarn, thus, leading to possible decrease in the strength of the yarn. Whatever be the fibre material, fibre architecture has been found to influence the composite properties based on the morphological and structural parameters (Bueno et al., 2002)
Cotton is one of the most common agro-based fibres that have enormous potential in composite manufacture due to its cost-effective, renewable, versatile, nonabrasive, visco-elastic, biodegradable, compostable and insulating characteristics. The cellulosic textile fibres are obtained from fibres that grow in a ball, around the seeds. Cotton has a high crystallinity index of about 87%. The crystallinity of cellulosic fibres can influence the mechanical properties of their composites (Carrillo et al., 2010).
The presence of surface impurities and the large amount of hydroxyl groups on plant fibres make them less attractive for reinforcement of polymeric materials. The attractive features of these fibres are light weight, non-toxicity, friendly processing and absorbed CO2 during their growth (Abdelmouleh et al., 2007; Tserki et al., 2005).
Alkali treatment has been known to modify plant fibres, promoting the development of fibre-resin adhesion, which then will result in increased interfacial energy and hence, improvement in the mechanical and thermal stability of the composites (Mwaikambo and Ansell, 2002). The uses of natural fibres to make low cost and eco-friendly composite materials are a subject of great importance.
Studies on woven and knitted cotton fabrics made from plied yarns and their use as reinforcements for unsaturated polyester resin, to the best of the author‟s knowledge, have not been reported yet. In this research work, four yarns were plied together to obtain 4-ply single strand which was then knitted and woven into different fabric architectures. The
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fabrics were treated with 20% sodium hydroxide for 1 and 2 minutes. Both the untreated and treated fabrics were used to reinforce the composite using unsaturated polyester resin as the matrix. The effects of these modifications on the surface characteristics and some mechanical properties of the fabrics and composite specimens were tested and analyzed.
1.1 STATEMENT OF RESEARCH PROBLEMS
Natural fibres can be used in many types of reinforcements and used for composites, such as continuous and discontinuous unidirectional fibres, random orientation of fibres, etc. By taking the advantages from these types of reinforced composites such as: good properties and reduced fabrication cost, they had been used in the development of automotive, packaging and building materials. The challenges here have always been the problem of low mechanical properties and incidence of fibre pull-out. Problem of low patronage of cultivated cotton lints especially in Northern Nigeria, as textile mills are struggling to remain in business, is a major concern for cotton growers. Also, there are very few reports on different fabric architectures and woven fabric composites reported so far.
Realizing the advantages of natural fibres, knitted architecture and woven pattern, these three factors would be considered in the present work. In this research project, cotton would be utilized as reinforcement because of its availability and ability to be produced in a continuous form, and hence could be produced into a woven mat form.
1.2 RESEARCH AIMS AND OBJECTIVES:
1. To characterize the properties of the plied cotton yarn.
2. To weave and knit the yarns into fabrics of different architectures.
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3. To evaluate the effect of alkali treatments using sodium hydroxide (NaOH) on the properties of knitted and woven cotton fabrics
4. To prepare the cotton fabric-reinforced composites using hand laying technique and study of the effect of alkali on the reinforced unsaturated polyester composites.
5. To study the effect of different laminate configurations (2-ply laminated composites) on the properties of hybrid knitted and woven cotton fabrics reinforced unsaturated polyester resin composites.
6. To evaluate some of the mechanical properties of the reinforced composites (tensile strength, flexural, impact strength and hardness)
7. To achieve a better understanding of composite properties in the special case where the fibre part is of different architectures.
8. To introduce new class of materials that might find some industrial applications.
1.3 JUSTIFICATION
Due to poor patronage (or sale) of grown cotton as many textile mills are going out of business, the use of cotton for composite reinforcement provides an alternative market for cotton lint products. Composites of different fabric architectures are aimed at solving the problem of low mechanical properties and incidence of fibre pull-out. Some authors have noted the possibility of slightly altered mechanical properties depending on whether the yarns are twisted prior to weaving, (Naik and Shembekar, 1992b) and work in this area have shown that damage accumulation under static and cyclic loading is different in laminates fabricated from twisted or untwisted yarn. (Marsden et al., 1994)
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Also, the usage of woven composites has increased over the recent years due to their lower production costs, light weight, higher fracture toughness and better control over the thermo-mechanical properties.
1.4 SCOPE OF THE STUDY
The scope of the research work is as stated below:
1. Twisting together of four (4) single cotton yarns of known count.
2. The weaving and knitting of the twisted yarns into fabrics of different architectures.
3. Surface treatment of the fabrics with 20% concentration of Sodium hydroxide at different conditions.
4. Finally, the reinforcement of unsaturated polyester matrix with the knitted and woven cotton fabrics to form the reinforced composites.
5. Analysis of the tensile properties of the fabrics and the mechanical properties of the composite samples via:
Universal Testing Machine (Tensile and Flexural test)
Charpy Impact test (Ability of the composite to absorb shock)
Indentec Universal Hardness Testing Machine (Hardness of the composite).
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