Water Absorption Behavior of Biocomposites

All polymer composites absorb substantial amounts of moisture or water in humid environment as well as in water. The most important concern in indoor and outdoor applications of natural fiber-based biocomposites with polymer matrices is their sensitivity to water absorption, which can reduce considerably their mechanical, physical, and thermal properties and performances. The water absorption of biocomposites results in the debonding or gap in the natural fiber-polymer matrix interfacial region, leading to poor stress transfer efficiency from the matrix to the fiber and reduced mechanical and dimensional stabilities as well [158]. It has been known that the hemiceUulose component in cellulose-based natural fibers may be mainly responsible for water absorption because it is more susceptible to water molecules than the crystalline cellulose component. Also, poor interfacial adhesion 

In order to eliminate the hemiceUulose component and, consequently, to increase the water absorption resistance, alkah treatment of natural fibers has often been conducted in diverse biocomposite systems, for example, sisal/phenolic [120] and natural fiber/glass fiber hybrid UPE [76]. Mishra et al. [76] reported that the water absorption of pineapple leaf fiber/glass hybrid and sisal/glass hybrid composites was 7% less than that of the unhybridized composites and the absorption was further reduced by 6% by fiber surface treatments before composite processing, compared with the untreated fiber/glass hybrid composites. 

In addition, many other approaches for treating the surfaces of natural fibers such as coupling agents, polymer coating, enzyme modification, and acetylation to increase the water absorption resistance through the improvement of fiber-matrix interfacial properties have been attempted [60, 147, 152, 159], 

Each method has some advantages and disadvantages, as noted. Industries are interested in simpler, cheaper, and faster processes, suitable for industrial adoption. 

With increasing social consciousness and global awareness, both academia and industries should also consider labor-friendly, environmentally friendly, and highvalued processes for the twenty-first century materials. In addition, it is necessary to maintain a constant product quality. Less expensive surface treatment should be used for biocomposites to replace glass fiber composites in current and potential applications in the future [161]. 

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