Mechanical properties of hollow fibrous silica from rice husk as a reinforcing filler for polypropylene composites

• RHFS enables high-performance composites without complex pre-treatments. • RHFS increases the yield stress and elastic modulus of polypropylene (PP) composites. • RHFS achieves a synergistic balance of stiffness, strength, and impact toughness. • The fibrous structure of RHFS provides an effective mechanical anchoring effect. The development of fillers is a crucial area in enhancing diverse properties of polymer materials. There has been increasing demand for plant-derived fillers from the viewpoint of environmental impact. Silica, along with cellulose and hemicellulose, is a component of rice plant biomass. The present work focuses on rice husk fibrous silica (RHFS), a fibrous, tapered, and hollow silica structure derived from rice husk waste. Focusing on its unique morphology, this study investigates how the reinforcing mechanisms—governed by the aspect ratio and hollow-shell architecture of RHFS—contribute to the mechanical properties of polypropylene (PP) composites. PP composites containing RHFS and maleic anhydride-grafted polypropylene (MAPP) were fabricated via injection molding, followed by characterization through tensile tests, scanning electron microscopy (SEM), and X-ray computed tomography (X-CT). The incorporation of 30 wt.% RHFS increased the tensile strength and elastic modulus of the PP composites by up to 1.3-fold and 2.0-fold, respectively. X-CT analysis revealed matrix fracture at the composite fracture surface, while SEM and CT imaging confirmed matrix infiltration into RHFS hollows, supporting its reinforcing function. Impact strength also improved with RHFS content, indicating its energy-absorbing capability. Thermogravimetric and Fourier-transform infrared spectroscopy (FT-IR) analyses further demonstrated the thermal stability and interfacial interactions contributing to composite performance. Given the global abundance of rice husk and the eco-friendly nature of RHFS, this study highlights its promise as a low-cost, carbon-neutral alternative to conventional fillers in polymer composites.