Critical length and interfacial strength of PALF and coir fiber incorporated in epoxy resin matrix

The several advantages of natural lignocellulosic fibers (NLFs), such as, economical, technical, environmental and social, make these fibers an alternative to replace synthetic fibers in composite materials. The application of NLF as reinforcements in polymeric composites has increased in many industrial sectors from civil construction to automobiles. This demands the characterization of promising fibers, such as those extracted from leaves of pineapple (PALF) and the mesocarp of coconut fruit (coir fiber), for possible application in composites. In the present work, pullout tests were performed to compare the interfacial adhesion with epoxy resin of these two fibers that have greatly different characteristics. Results showed a critical length 70% higher for the coir fiber in comparison to PALF and a interfacial strength 3.5 times smaller, which indicates stronger adhesion of PALF with epoxy resin. This may be justified by the distinct morphological aspects, particularly the rougher surface of PALF. Mechanical tests were also performed in both coir fiber and PALF composites. In these tests, it was observed the superiority of mechanical properties for the composite reinforced with 30 vol% of PALF. Additionally, ballistic tests were carried out. In this evaluation, composites were used in a MAS type III against the 7.62 mm ammunition. The results revealed a relatively low depth of penetration (18.2 mm) for the MAS with PALF composite as well as a depth of penetration (31.6 mm) for MAS with coir composite, both considered efficient according to the personal body armor standard. Therefore, all these results highlight the potential of these fibers as polymer composites reinforcement in ballistic armors.