Biocomposite impact properties

Figure 4.14 indicates that the incorporation of kenaf fibers increased the Izod impact strength compared to neat PLA and the alkali treatment of kenaf further increased the strength of kenaf/PLA biocomposites with 40 wt% kenaf fiber content [51]. Silane treatment did not contribute to the enhancement of the impact strength in the case studied. The explanation for this was that the superior impact property of PLA/FIBNA was attributed to the increased fiber-matrix adhesion, the removed surface impurities, and thereby the formation of rough fiber surfaces. 

Blending different biofibers could result in biocomposites with balanced properties. Engineered biofibers, defined as the suitable blend of surface-treated bast and leaf fibers as shown in Figure 13.8, have been studied and reported. By manipulating the blend ratio of biofibers, an optimum balance in mechanical properties of the resulted biocomposites could be attained. For example, kenaf- and/or hemp-based composites exhibit excellent tensile and flexural properties, while leaf fiber (PALF) composites have high impact properties. The combination of bast and leaf fibers is expected to achieve a balance of flexural and impact properties of the targeted biocomposites [49]. 

Huda et al. [37] reported the flexural and impact properties of PLA/kenaf fiber biocomposites with alkalization and silane treatment of fibers. All surface-treated kenaf fibers showed the tendency to significantly increase the flexural modulus compared to neat PLA. The flexural strength of the PLA composites decreased with the addition of kenaf fibers probably due to poor adhesion between the kenaf fibers and PLA. With 40 wt% kenaf fiber content. 

Consequently, it is worth overviewing extensively current research efforts on the effects of surface treatment of natural fibers on the properties of biocomposites in terms of interfacial, static mechanical, dynamic mechanical, impact, thermal, physical, morphological, fracture behavior, and water absorption. In the present chapter, the description and information focus mostly on the results reported in recent years. 

Starch is one of the most widely used biopolymer in biocomposites because of its low cost and versatility. A plasticizer like glycol is sometimes used to make it suitable for processing. It is also blended with other polymers like aliphatic polyesters to improve its physical and mechanical properties. Biocomposites based on starch matrices show improved properties, which are comparable to E-glass/epoxy composites. Tensile, flexural, impact, and creep properties of these biocomposites are significantly better than those of neat starch. Various biofiber surface treatments have been shown to improve the properties of starch-based biocomposites. 

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