Characterization of kenaf and glass fiber reinforced hybrid composites for underbody shield applications

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With an objective to make automotive parts environmentally friendly by replacing glass fibers with natural fibers for underbody shield application, this paper investigates the water absorption behavior of three types of compression-molded composites: all-glass (25% by wt.), all-kenaf (25% by wt.) and hybrid (12.5% glass and 12.5% kenaf by wt.) with polyethylene terephthalate matrix and Acrodur® binding agent at ambient (23 °C) and elevated (70 °C) temperatures. Specimens saturated at ambient temperature were then subjected to various hygrothermal conditionings: freeze-thaw cycling between 23 °C and −29 °C; extended freeze at −29 °C; and re-drying. Standard flexural tests showed the degradation in mechanical properties was a strong function of water absorption. At dry conditions, both flexural modulus and strength for hybrid and all-kenaf composite were much higher compared to all-glass composite. After saturation, the mechanical properties of all-kenaf and hybrid composite, despite being significantly affected by water absorption, were comparable to the saturated all-glass composites. As expected, the mechanical properties of composites saturated at 70 °C were severely affected where the modulus decreased by about 55% for the hybrid and all-kenaf composites. However, freeze-thaw cycling and extended freeze did not have any significant impact on the mechanical properties of the saturated composites. Interestingly, the flexural strength for all composites increased after the saturated specimens were re-dried. This phenomenon was attributed to the added crosslinking in the Acrodur matrix. Also, sound absorption tests and muffler tests showed that glass fibers can be replaced by kenaf fibers without compromising the performance.