The Use of Natural Fibre Composites - Case Study Example

A REPORT ON NATURAL FIBRE COMPOSITES By of the of the of the School 25 May Introduction The use of natural fibre composites in Engineering and construction is one of the oldest technologies in the industry predated in the ancient Egypt many centuries ago. It was adopted and used by most industrialized countries until the development of high-tech artificial fibre like the durable carbon and glass fibre that went on to dominate the market. However, these advanced fibre composites had their own shortcomings, especially in costs accrued in manufacturing and production. With the growing environmental concerns around the world, there are various attempts for the industry to ‘go green’ by increasing their use of environmental friendly materials. The engineering industry has focused its interests once again to use of natural fibre composites as bio composites with positive environmental outcomes. In order to substitute and compete effectively with other fibres, fibre treatments have extensively been used to improve and strengthen natural fibre (Brouwer n.d.). Animals and plants are rich sources of natural fibre. Description of the materials Plant fibre has found extensive use, because it is easily grown and is easily accessible. Plant fibres come in various forms; leaf, seed, fruit, and bast fibres, and have wide applications based on their properties. From the leaf are examples of Abaca and sisal fibre characterised by sturdiness and roughness. Cotton wool is the most commonly used seed originating fibre, while kapok and coconut fibre come from the fruits. Bast fibre has the most uses and produces length yarns; its characterised by high stiffness, obtained from the stems and entails wood, jute, flux, hemp, kenaf, Bamboo straws and ramie among others. These fibres are often used as reinforcement materials in composites either as wood or non-wood fibre. Composition of natural fibres Natural fibres consist of different chemical elements that determine their differences in physical properties. According to Westman et al (2010 p. 4), the primary constituents of natural fibre are “cellulose, hemicelluloses, pectin and lignin, whose individuals percentage varies with the type of the fibre, and their growing and harvesting conditions.” These chemicals are contained in the cells of the fibre and some decline during fibre processing. For example, cotton has high cellulose and Flax and hemp with high hemicelluloses than other fibres. On the other side, sisal has high lignin and Pectin components compared to the rest. In addition to these polymers are water, waxes, inorganic and organic components, which all can influence the fibre’s mechanical appearance and performance. The major cellulose components are crystalline in nature and consist of anhydroglucose molecules capable of high level polymerization. In natural fibres, cellulose fibrils are often embedded in a lignin. Hemicelluloses chemical is a complex polymer composed of approximately 5carbon sugars in fibre bundles. Pectins, hemicellulose and lignin function as chemical adhesives and matrixes to bond together cellulose fibre bundle (Clemons 2010). Together, hemicelluloses bonding to cellulose micro-fibrils through its hydrogen element creates cellulose-hemicelluloses network (Thomas and Pothan 2008, p. 256). Structure of natural fibre composites The chemical composition of natural fibre entails polymers of glucose molecules made up of HO groups. Barnett and Eronimidis (2003, p. 55) state that cellulose units result from gylcosidic bonds through “bonding of two glucose molecules by elimination of a water molecule”. Unlike cellulose, hemicellulose consists of different and weaker monomers, while pectins and lignin are complex polysaccharides characterised of irregular bonds of hydroxyl. See the chemical representation of their structure on figure1below. Figure1: Structural chemical composition of natural fibre composites (Westman et al. 2010, p. 5). These plant fibres occur in hierarchical form from the micro fibrils into the fibre bundle itself. It is the cellulose elements that collect into chains of cellulosic macromolecules. Although the major components, they require hydrogen atoms to bond them closely. Alone, the cellulosic structure stands weak, but when combined with matrixes of hemicellulose and lignin, the rigidity of the micro-fibrils is enabled (Cristaldi et al. 2010). (Cristaldi et al. 2010, p. 322) Properties of natural fibre composites Moisture absorption: It a major limitation in use of natural fibre composites. Most have higher moisture absorption compared to glass and carbon manufactured fibres, which contributes to the fibre swelling to impair their applications. Therefore, as polymers placed in humid conditions, they absorb moisture than other synthetic fibres. Those with high cellulose content tend to absorb and retain more water in their cells, which means that during harvesting and processing, control of temperature is critical. Kishore and Rao’s (1985) research reveals that sisal more than jute fibres, has higher cellulose content and demonstrated higher water absorption level; this can be attributed to its physical and chemical properties. Hydroxyl elements form covalent bonds with hydrogen atoms which facilitates absorption of moisture in natural fibre composites. Density: The microstructure of natural fibres demonstrated hollow portions of the material in nature that contributes to their generally reduced weight. Compared to glass fibre, the highest level of a cell density in natural fibre is relatively low. Clemons (2010) compares the upper limit density of 1.5 g/cm3 in a natural fibre cell with over 2.0 g/cm3 in glass fibre, which depicts the light weight element of the natural fibre composites. Although the original weight stands low based on the compositions, it can be altered during processing due to temperature and moisture elements. This may increase the weight of the fibre, but its maximum density remains suitably low. Tensile strength: Natural fibre composites major shortcomings occur in its strength capacity. It has low strength property compared to glass fibre, which can be attributed to incompatibility issues with resin binder to the reinforcement natural fibre, and dampness due to their moisture uptake. They are also affected by processing methods, which weakens existing bonds of the chemical elements. For example, retting process is known to eliminate pectin components from the fibre composites and as a binder, reduces the lateral strength of the fibre bundles. Their tensile strength depends on the type of fibre, which makes hemp and flux to have greater strength compared to cotton. Some like flax increase their strength with absorption of moisture. Compared to glass, most natural fibre composites’ tensile strength ranges below 1000 N/mm2, with only an exception of flax that can exceed, but is lower than the former’s range of over 2000 N/mm2. Elongation of failure: The improvement in their tenacity allows them to have higher elongation to break and makes them competitive fibres in production of stiff and stronger materials. Flax fibre now competes effectively with synthetic and glass fibre when seeking to produce hard and resistant products in the industry. Costs of natural fibre composites The composites’ use has economic gains in the industry compared to the synthetic and glass fibre composites, who’s manufacturing process leads to high costs of the final products. Low cost of the natural fibre attracts massive consumers in the industry to evade the expensive alternatives. Fibre and synthetic fibre composites cost almost thrice the market price of natural fibres. Referring to Joshi et al. (2003 p. 371), “glass fibers used for composites have a density of 2.6 g/cm3and cost between $1.30 and $2.00/kg, compared to flax fibers measured to have a density of1.5 g/cm3and that cost between $0.22 and $1.10/kg”. Therefore obtaining of raw materials is cheaper and competitive, which translates to less expensive end products. Environmental friendly The recyclable feature of natural fibre composites enables increased use of the products, which support the ecological systems. It is possible to re-use the materials in production, which goes on to reduce wastage and pollution in the environment. Through mechanical recycling, natural fibre composites become sources of other raw materials for secondary products. These renewable sources result in production of bio-based eco products capable of biodegrading. Plants natural fibres are rich sources of bio-polymers used in development of thermoplastic composites. The sources of raw materials come directly from easily replenished vegetation that is only dependent on climate and nature. Natural fibre materials are not only available, but can be replaced through human cultivation for their sustainability. They create a source of income for producers (e.g. sisal farmers) and in their re-use from wastage through recycling. Cultivation of natural fibre facilitates environmental conservation by re-use of emitted carbon emission in plants, in turn releasing oxygen to the environment. When natural fibre materials are disposed, they are biodegradable. They decompose easily with the help of micro- bacteria, turning into organic nutrients that can be used again by the plants. Processing and methods Compression moulding: This method entails use of force and pressure application in the moulding process for various composite products. By using two metal plates, with the stationery one at the base and the movable at the top, the slug (reinforcement and matrix compound) is compressed into a desired shape. First, under high selected temperatures, the material melts down and when pressure is applied through the hydraulic press, the compound becomes compressed into the shape of the mould. Pressure and heat are maintained in the compressing moulding process for the polymer to cure. Afterwards, the compressing upper metal plate is released and the mould cavity is opened to remove the composite product processed into a desired shape. It can be able to use fibre yarns efficiently without high wastage. Injection moulding: Unlike in compression, the composite compound to be moulded is placed in a closed mould. The method is commonly used in moulding of short natural fibre reinforced plastics. It is dependent on the temperature, pressure maintenance and the injection speed of the molten compound. First, the natural fibre composites in granules are melted, then in the injection machine, as the screw moves backward, it pushes the melded compound forward in the melting zone towards the cavity. Periodically, the screw pushes the compound in injections down the mould cavity by applying pressure until it fills up (Colton 2009). Taking the shape of the mould cavity, the melted compound is allowed to solidify. Finally, the mould tool is opened by moving metal plates that form the mould cavity to release the processed composite product. Others are pultrusion methods. Filament winding makes use of creels for holding and pulling roving packages in manufacturing of circular surfaces. These methods consume lower embodied energy in processing compared to synthetic and glass fibre composites. Applications Natural fibre composites currently have massive use in the automotive industry. Flax which has more dense character is used for reinforced car roofs. Bast fibres have gained increased use in the automotive industry as fibre reinforced plastics for inner and outer parts. Examples are the dashboards, head and trunk liners and the seat backs. The construction industry has also increased use of wood fibre as reinforcing composites in raising walls and roofing. Other than framing, the natural fibre makes high standard door panels for both buildings and automotives, also used for decking and railing. In electric and electronic industries, natural fibre composites are used in manufacture of light weight casing for computing gadgets such as laptops and cell phones. Combined with PP and other components, natural fibre gets wide applications, which serve best to increase its resistance to damage, weight reduction on equipment and meeting favourable market demands. Numerous items for sports are adopting natural fibre fabrics, just as in the textiles industry for manufacturing tents, sails and packing bags. Conclusion Natural fibre composites are competitive products in the construction and engineering industry, currently attracting a wide number of consumers for their environmental friendliness, weight and cost effectiveness in products. Most natural fibre comes from plants and is composed of chemical constituents like cellulose, hemicellulose, pectins and lignins among others, which determine the mechanical properties and performances. They generally have low density, high moisture absorbency and high capacity of elongation to break, but are relatively weak in tensile strength compared to other synthetic and glass fibres. Compression and injection moulding processes are commonly used which entail use and control of high temperatures and pressure to create the composite products. Applications of natural fibre composites are extensive in the automotive, construction, electric and electronics industries. Appendix HO - hydroxyl groups PP- polypropylene References Barnett, J. and Jeronimidis, G. Eds., 2003. Wood Quality and its Biological Basis. Oxford: John Wiley & Sons. Brouwer, W. D., n.d. Natural Fibre Composites in Structural Components: Alternative Applications for Sisal? [online] Available at: [Accessed 25 May 2015]. Clemons, C. M., 2010. Natural Fibres in ‘Functional fillers for plastics’ edited by Marino Xanthos. [online] Available at: [Accessed 25 May 2015]. Colton, J. S., 2009. Injection Molding - process Description. [online] Available at: [Accessed 26 May 2015]. Cristaldi, G., Latteri, A., Recca, G. and Cicala, G., 2010. Composites based on Natural Fibre Fabrics. p. 317-339. [online] Available at: [Accessed 25 May 2015]. Joshi, S.V., Drzal, L.T., Mohanty, A.K. and Arora. S., 2003. Are natural fiber composites environmentally superior to glass fiber reinforced composites? Composites: part A vol 35, pp. 371-376. [online] Available at: [Accessed 26 May 2015]. Kishore, J. G. and Rao R. M. V. G. K., 1985. Moisture Absorption Characteristics of Natural Fibre Composites. Journal of Reinforced Plastics and Composites, vol 5, pp. 141-151. [online] Available at: < http://nal-ir.nal.res.in/1108/1/Jnarticles_RMVGK_8.pdf>[Accessed 25 May 2015]. Thomas, S. and Pothan, L. A., 2008. Natural Fibre Reinforced Polymer Composites: From Macro to Nanoscale. Philadelphia, PA: Old City Publishing. Westman, M. P., Laddha, S, G., Fifield, L.S., Kafentzis, T.A. and Simmons, K. L., 2010. Natural fibre Composites: A Review. [online] Available at: [Accessed 25 May 2015]. Read More