CHAPTER ONE
INTRODUCTION
Fibre reinforced polymer composites are being used in almost every type of applications in our daily life and its usage continues to grow at an impressive rate. The manufacture, use and removal of traditional composite structures usually made of glass, carbon and aramid fibres are considered critically because of the growing environmental consciousness [1]. In recent years, there has been a growing interest in the use of biofibres as reinforcing components for thermoplastics and thermosets. Coconut fibre (coir), a member of the palm family is a biodegradable and environmental friendly crop. Moreover, coir is a strong, stable and versatile material and it has been recognized as an important source of fibres for composites [2–4].
It is generally accepted that the tensile properties of fibre-reinforced polymer composites are controlled by factors such as nature of matrix, fibre-matrix interface, fibre volume fraction, fibre aspect ratio. Many scientists are working in this field and the reinforcement of polymer with coconut coir fibres has been widely reported [5–12]. A further attempt to use coir fibres as reinforcement for high temperature and pressurize vessel applications has been found in the literature [15]. Manikandan Naira et al. [16] studied the thermal behaviour of polystyrene composites reinforced with randomly matted coconut coir fibres by means of thermogravimetric and dynamic mechanical thermal analysis. It has been found [17] that matrix cracking, fibre bridging, fibre breakage and pull-out are the major fracture modes of coconut coir fibre reinforced composites with pre-cracks under the static loading condition. However, despite the fact that several methods have been used and great strides have been made, there is still some lack of knowledge about tensile strength property of coconut coir fibre reinforced polymer composites.
Cashew nut shell liquid resins (CNSL) are the most prominent examples of the class of thermosetting resins usually referred to as bio-resins [18], even though new research efforts are needed to address to offset its major disadvantage. The use of CNSL as a major resin matrix by the composite products industry is due to a number of advantages, including low cost, ease of use under a wide variety of curing conditions, low cure temperatures, water solubility, resistance to microorganisms and to abrasion, hardness, and excellent thermal properties.
The present work dealt with the changes in the tensile properties of coir/CNSL blend composite as a function of fibre size, weight fraction and surface treatments of coconut coir fibre. In addition to this, the effect of coconut coir fibre loading on water absorption tendencies of the composites has also been examined. Meanwhile, the surface modifications is studied and described. This study was initiated to determine whether the compatibility between CNSL and coconut coir fibre is strong or weak, and to evaluate the tensile performances of the composites. It is anticipated that this study may open the way for future investigations in the use of coconut coir fibre in fibre composites so that the range of natural fibre potential applications can be widened.
- Background
The growing interest in using natural fibres as a reinforcement of polymer-based composites is mainly due to their advantages such as lower cost, renewability, acceptable specific properties, lower density, ease of preparation, lower energy requirements for processing, biodegradability, wide availability, and relative non-abrasiveness over traditional reinforcing fibres such as glass and carbon. However, some limitations in using natural fibres in composites are the lower allowable processing temperatures, incompatibility between the hydrophilic natural fibres and hydrophobic polymers, and high moisture absorption of the fibres and the resulting swelling of the manufactured composite [19 – 20]. Thermosett plastics used in such composites consist of polyesters, epoxy, vylester and phenolic,. On the other hand, coir, jute, sisal, kenaf, flax, banana, wood flour, rice hulls, newsprint, pulp, and cellulose fibres are the main natural fibres used as reinforcement.
Natural fibre composites such as hemp fibre-epoxy, flax fibre-polypropylene (PP) and china reed fibre-PP are attractive material in automotive application particularly because of lower cost and lower density. Natural fibre composites are also claimed to offer environmental advantages such as reduced dependence on non-renewable energy/material sources, lower pollutant emissions, lower greenhouse gas emission, enhanced energy recovery and of life biodegradability of components [21].
Natural fibres such as banana, cotton, coir, sisal and jute have attracted the attention of scientists and technologists for application in consumer goods, low cost housing and other mechanical and civil structures. It has been found that these natural fibre composites possess better electrical resistance, good thermal and acoustic insulating properties and higher resistance to fracture.
Natural fibres have many advantages compared to synthetic fibres, for example low weight, low density, low cost, acceptable specific properties and they are recyclable and biodegradable. They are also renewable and have relatively high strength and stiffness and cause no skin irritations. On the other hand, there are also some disadvantages, for example moisture uptake, quality variations and low thermal stability. Many investigations have been made on the potential of the natural fibres as reinforcements for composites and in several cases the result have shown that the natural fibre composites own good stiffness but the composites do not reach the same level of strength as the glass fibre composite[22].
In the past, various studies have been carried out on natural fibre composite. Coir hemp, sisal, cotton, ukam, and bamboo are the most commonly fibres are used to reinforce polymers such as polyolefin, polystyrene, epoxy resins and unsaturated polyester, while the study of coconut coir fibre is still scarce. And the fact that coconut husk fibre is fibre that also obtained directly from natural resource and has cheap price make it even more attractive in terms of sustainability and environmental awareness. However, very limited studies have been reported available for information and data dealing with that tensile properties polymer composite reinforce with coconut coir fibres. In this study, coconut coir fibre for reinforcement and cashew nut shell liquid (CNSL) resin as a matrix for composite fabrication were selected. The main idea is to try to explore the new natural resources, considering abundance available material in Nigeria local nature.
The study is significant because it explore the potential of the abundant resources from plant waste for used as fibre in reinforced composite. The use of coconut coir fibre also has an economical advantage because glass or carbon fibre can be replacement fibre by coconut coir fibre. Although the use of coconut coir fibre based CNSL is not popular as a mineral or inorganic fibre, CNSL – derived coconut coir fibre.
The significance of this study is to generate the idea and to try to explore the new natural resources with low production cost considering on abundance available in natural plant fibres particularly, in Nigeria tropical forest.
In this work, a study on the effects of process parameters on the tensile properties of new series of green composites involving coconut (coir) fibre as a reinforcing material in cashew nut shell liquid (CNSL) resin based polymer matrix has been presented. Static mechanical properties of randomly oriented intimately mixed coconut (coir) fibre reinforced polymer composites such as tensile strength and modulus were investigated as a function of fibre condition (untreated and alkali treated), fibre sizes (1, 3 and 3 mm) and percentages (5%, 10% and 15% by weight). The aim of this study is to investigate the technical viability of coconut coir fibre as CNSL composite reinforcement. The goal of this work is to understand the changes of tensile strength under various process parameters as a function of influences of fibre sizes, contents and treatments. Fracture rupture of tensile test specimens were examined under tensile loading to get an idea about the fracture behavior.
- Problem Statement
In the context of challenging environmental issues and a global energy crisis, bio-based materials are attracting increasing levels of research interest, from both academia and industry, because of their numerous advantages: renewable resource usage, low cost, biodegradability, and so on. Natural fibres such as coconut, hemp, ukam and sisal have been identified as attractive candidates for the reinforcement of thermoplastic polymers. They are cheap, abundant and renewable, and have good specific properties due to their low densities. Until recently, natural fibre reinforced polymers were used mainly in the construction and automotive industries. These markets are rapidly expanding. Other applications requiring high mechanical performance are envisaged, in order to enhance and highlight the properties of this plant-based resource. Naturally, the strength and load-bearing capabilities of composites are directly dependent on the properties of their constituents (fibres and matrix), their microstructure, and their interfacial bond strength. Some results, previously published by Bodros et al [23], are very encouraging and point towards the possibilities of structural applications.
Nevertheless, contrary to classical synthetic fibres (carbon, glass), the behaviour of plant-based fibres depends strictly on their process parameters, as emphasized for example by Davies and Bruce [24]. Classically, during the manufacturing of composites, the process parameters are chosen in accordance with the nature of the polymer matrix. For polymers reinforced with natural fibres, so many factors considered. The influence of fibre sizes, treatment and content are relatively well investigated (Funaoka et al. [25], Passard and Perré [26]).
Nonetheless, considerable differences exist for vegetable fibres stemming from annual plants such coconut fibres, in terms of both structural and biochemical composition, and mechanical properties depending on the processing technique used. Literature on the topic of the tensile properties of natural fibres is unfortunately poor. The limited tensile toughness of natural-fibre-reinforced thermosett plastics at high strain rates can preclude their use in some applications. To understand and ultimately improve the tensile performance of these composites, one must thoroughly understand the effects of various composite manufacturing processes and how it affects tensile. Because of methodological difficulties, little work has been performed on characterizing the process parameters such as fibre size, fibre content and fibre orientation distribution in natural-fibre-reinforced polymer based composites. Even less has been done relating processing parameters to composite performance. This research was undertaken to explore the effect of various composite process parameters on the tensile toughness of coconut coir fibre-reinforced CNSL resin composite.
Generally, mechanical properties of a composite are dependent upon the properties of the matrix and reinforcement, the interaction between the matrix and reinforcement, amount, type, arrangement of the fibres within the composite, and fabrication process [27]. Properties of composites are determined through experimental measurements. Experimental methods may be simple and direct. However, one set of experimental measurements determines the properties of a fixed fibre–matrix system produced by a single fabrication process. Additional measurements are required when any change in a system variable occurs such as relative volumes of the constituents, constituent properties, and fabrication process. Experiments may become time consuming and cost prohibitive. Mechanics based models and semi-empirical methods of determining composite properties can therefore be useful to predict the effects of a large number of system variables [28].
1.3 Research objectives
The objectives of the study are:
- To characterize the properties of coconut fibre-reinforced CNSL composites.
- To investigate the effects of varying process parameters, such as fibre condition (untreated and alkali treated), fibre sizes (short and long fibres) and percentages (10%, 20%, 30% and 40% by volume) on the tensile properties of coconut fibre-reinforced
- To find the maximum tensile strength and Young Modulus of these composite laminates
1.4 Research Scopes
The study involved both the testing of hand lay-up and compression moulded coconut fibre-reinforced CNSL resin composite with respect to its tensile characteristics. The composite laminates were tested for the following process parameters:
- fibre loadings (10%, 20%, 30% and 40% by volume),
- fibre sizes (0.625 – 1.2),
- fibre aspect ratio (short and long fibres), and
- fibre surface treatment (untreated and treated fibres).
1.5 Organization of thesis
In this thesis, the background theory and the relevant literature survey are presented in the first chapter and second chapter, respectively. This is followed by chapter three, where theoretical considerations needed for this work is given, and is followed by chapter four where descriptions of all the materials and methods used in experiments characterization and test procedures are explained. Chapter five contains the details of the results and discussion. Last but not least, chapter Six presents the conclusions of this thesis and some suggestions for future works.
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