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Top1. Introduction
Nowadays the use of synthetic fiber reinforced composites and petroleum-based polymers is limited due to their non-bio degradable and non-recyclable nature. The use of synthetic fiber for fabrication of different material leads to a threat to the environment across the world. Hence, recent research focus is targeted towards development of green products causing little or no damage to the environment. Accordingly, consideration of a new fiber (natural) and fabrication of new type composite material is the need of hour (Ball et al., 2019). Bio-based fibers have some plus characteristics over synthetic fibers such as abundant availability, low cost, eco-friendly, recyclable, light in weight, high specific strength, and high stiffness etc. They are non-abrasive and hypoallergenic in nature and also, possess ease of manufacturing/processing (Sreenivasan et al., 2012; Sreekumar et al., 2009; Zaman et al., 2010; Herrera-Franco & Valadez-Gonzalez, 2004). The plants, animals and minerals are the source of natural fibers. The natural fibers derived from plants generally have high cellulose content and they are widely used for the manufacture of green composite materials. Literature has explored the ability of different bio fibers as reinforcement in composite industries such as Jute (Ashraf et al, 2019; Burrola-Núñez et al., 2019), Sisal (Nagamadhu et al. 2019; Megiatto Jr et al., 2007), Kenaf (Hamidon et al., 2019), Banana (Senthilkumar et al., 2018), Bamboo (Zubaidah et al., 2018), Hemp (Sepe et al., 2018; Sunny et al., 2020), Coir (Adenivi et al., 2019), Flax (gassan et al., 1999; George & Verpoest, 1999), Aloe Vera (Chaitanya & Singh, 2016; 2018) and pine apple leaf fiber (Todkar & Patil, 2019).
However, the compatibility between natural fiber and matrix is an issue, hence, the natural fibers have limited use in the polymer industries. The properties of bio composite materials are dominated by interfacial interaction between matrix and lingo-cellulosic fibers. The existence of hemicelluloses, lignin and other materials is the reason for weak intermolecular adhesion between matrix and reinforcing material (Maldas & Kokta, 1994; Zhou et al., 2016). These issues of the natural fibers can be remedied by surface modification or through carbonization process. The surface modification may be physical, chemical or biological (Valadez-Gonzalez et al., 1999). One possible way to change the surface of the natural fiber is to reduce the nature of hydrophilicity due to chemical treatments and chemical modification. The chemicals used to treat fiber play an important role in enhancing the ability to strengthen the natural fiber. The interfacial bonds between matrix and filler materials can be increased due to coupling agents. The coupling agents are also responsible for reduction of moisture of the natural fibers. Several chemical treatment approaches are adopted for surface treatment of natural fibers such as alkaline treatment, benzoyl chloride treatment, permanganate treatment, acetylation treatment, saline treatment and peroxide treatment, etc. (Chandrasekar et al., 2017; Fiore et al., 2015; Majid et al., 2016; Kalia et al., 2019; Li et al., 2007; Kaushik et al, 2012; Liu et al., 2019). The alkaline treatment of natural fiber is carried out by using aqueous sodium hydroxide (NaOH) particularly in the case of thermosetting and thermoplastic composites and corresponding chemical reaction is given in Eq. (1). This treatment enhances the surface irregularity resulting improved mechanical anchoring leading to improved matrix fiber interpenetration (Nair et al., 1996).
