Effect of hybrid eco-friendly reinforcement and their size on mechanical and flame retardant properties of polypropylene composites for technical applications

While the potential of natural fiber (NF) composites for various engineering applications is well-recognized, a deep understanding of the intricate interactions within these composites remains crucial. This study examines the microstructural characteristics of the polymer matrix and evaluates the impact of reinforcement size, with a particular focus on fire sensitivity. Hybrid-reinforced polypropylene (PP) composites were introduced using a unique tri-hybrid system. This system combines long flax fibers (LFF) as primary reinforcement, with short basalt fibers (BF) and micro rice husk powder (RHP) as secondary reinforcements. These composites were fabricated using innovative extrusion, compression, and injection molding techniques. This novel fabrication method and strategic hybrid design bridged gaps in the composite structure, leading to significant enhancements in tensile and flexural strength. Improvements of 57.82%, 67.53%, and 60.02% over LFF/PP composites were observed, respectively. On the thermal front, the char residue surged by an impressive 497.51%. Flame properties, notably pHRR and THR, were reduced by 57.25% and 13.28%, respectively. These enhancements are attributed to the lignin in BF and the silica in RHP. The fire safety index further confirmed these improvements, with FGI and FPI increasing by 27.33% and 111.11%, respectively.