Mechanical, thermal and interfacial performance of sustainable polypropylene hybrid composites reinforced with short woven hemp fibers, basalt fibers and wheat straw ash

Abstract

The growing demand for sustainable lightweight materials has encouraged the development of hybrid polymer composites reinforced with natural fibers and agricultural waste. In this study, polypropylene (PP) hybrid composites reinforced with short woven hemp fibers (SWHF), chopped basalt fibers (BF), wheat straw ash (WSA), and maleic anhydride-grafted polypropylene (MAPP) were developed and systematically investigated. The experimental program was conducted in two stages. First, the basalt fiber content was optimized by incorporating 5-25 wt.% BF into PP containing 25 wt.% SWHF. The optimized formulation was then modified by adding 6, 12, and 18 wt.% WSA with a constant MAPP content. The composites were fabricated by twin-screw extrusion followed by injection molding and characterized using tensile and flexural tests, scanning electron microscopy (SEM), Fouriertransform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Incorporation of 20 wt.% BF significantly improved the tensile and flexural performance of the hemp fiber-reinforced PP composite. WSA further enhanced stiffness, while MAPP improved fiber-matrix and filler-matrix interfacial adhesion. SEM revealed improved fiber encapsulation, reduced interfacial defects, and more homogeneous filler dispersion. FTIR confirmed enhanced interfacial interactions without significant alteration of the PP structure. TGA demonstrated improved thermal stability and increased residual char yield. Among the investigated formulations, the 25SWHF/20BF/PP-6MAPP-12WSA composite exhibited the best overall balance of tensile strength, flexural performance, stiffness, and thermal resistance. The findings demonstrate the potential of WSA as a sustainable silica-rich functional filler for high-performance PP hybrid composites.