Effect of hybridization on crystallization behavior, mechanical properties, and toughening mechanisms in rubber-modified polypropylene flax fiber composites

Nowadays, the significance of sustainability has urged composite manufacturers to replace traditional synthetic fibers with eco-friendly natural alternatives due to their environmental and economic benefits. This work aims to fabricate hybrid polypropylene (PP) composites with short flax fibers, octene-ethylene copolymer (POE) rubber particles, and maleic anhydride-grafted polypropylene (MAPP) compatibilizer. The main goal is to gain an insight into the combined effect of toughening mechanisms induced by the short fibers and rubber particles at the crack tip and wake of composites, which is a crucial step in reaching a balance between toughness and rigidity. In this regard, a novel microscopy strategy is taken to elucidate the operating mechanisms at the crack tip and crack wake of composites. Also, differential scanning calorimetry (DSC), tensile, and Charpy impact tests were employed to investigate the effect of hybridization on the crystallization behavior, tensile, and impact properties of composites. The experimental results showed that the combined effect of encouraging matrix plastic deformation and synergistic work of toughening mechanisms at the crack tip and wake in the MAPP-modified hybrid composites containing 30% flax fibers and 10% POE rubber particles yielded an optimal improvement of 315%, 135%, and 37% in impact strength, elastic modulus, and ultimate tensile strength, respectively, over the neat PP formulation.