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Composite materials made from natural fibers were recognised from centuries ago. In the old age, straw and clay were used as a reinforcement and matrix material, respectively for the purpose of building wall construction. In the later stage, natural fiber lost its glory after introduction of more durable materials such as metals and alloys. However, these materials suffer from a number of limitations like expensive and laborious processes required for extraction to production, complicated product design, indications of irritation among sensitized people during handling and ultimately issues related to disposal of waste materials. Thus, over the last few decades the use of composite materials got accelerated, when glass fibers (as reinforcement) in combination with tough resins such as epoxy and polypropylene (matrix) could produce bulk composites with high strength and rigidity (Sathishkumar et al, 2014). In addition to glass fibers, other man-made fibers such as carbon (Visal and Deokar, 2016), aramid (Kalantar and Drzal, 1990), kevler (Dong et al, 2018) and boron fibers (Parker, 1974; Hume, 1938) are also used for the fabrication of composite specimens. They are acknowledged broadly in aerospace and automotive applications. However, the synthetic fibers have some bottleneck properties such as low elastic modulus, (so the products have low rigidity and easily deformed), low inter laminar shear strength, low long term temperature resistance and above all non-biodegradable (Tsai and Etzel, 2000).
Natural fibers are more useful as reinforcement in polymer composite industries and can replace synthetic fiber without compromising the quality of the materials. The advantages of natural fibers are biodegradability, low specific weight, high specific strength and stiffness (compared to glass), low raw material cost, friendly manufacturability, no skin irritation, low tool wear and also good thermal properties (Saheb and Jog, 1999; Joshi et al, 2004; Bogoeva-Gaceva et al, 2007). Several researchers have reported the properties of different fibers and their applications. Jute fiber shows high specific strength and high aspect ratio (Rohit and Dixit, 2016). Pine apple fiber has excellent thermal, mechanical and physical properties (Fadzullah and Mustafa, 2016). Coir fiber which are abundantly available is more long-lasting fiber than other natural fibers and able to resist salt water (Pecas et al, 2018; Verma et al, 2013). Hemp fiber has excellent tensile strength and tensile modulus (Carus, 2017). Bamboo fiber has advantages like fastest growing plant, requires very less amount of water to survive, light, strong and also stiffer than glass fiber (Shah et al, 2018). Coir fibers and wood fibers are used for the production of containers, boxes, packaging materials and modular house construction (Gunay, 2018). Flax and hemp fiber reinforced composites are used for green wall panel, racing bicycle and for musical instruments (Brief, 2011). Although these are used in different sectors but the applications are very limited because they have some disadvantages such as poor moisture resistance which causes swelling of the fiber and hydrophilic nature (low wetting with hydrophobic polymer). To overcome the difficulties of natural fiber, different techniques are adopted such as addition of nano filler material to natural fiber, surface modification by chemical treatments, and carbonization of natural fiber etc. (Naik et al, 2020a, b).