Influence of Hornification Treatment and Fiber Length on the Performance of Recycled Polypropylene Composites

The growing accumulation of plastic waste has driven its reuse in the development of new composites, with natural fibers emerging as promising reinforcements. However, their hydrophilic nature limits compatibility with polymer matrices. Physical treatments, such as hornification, can reduce hydrophilicity and improve fiber–matrix adhesion. As it does not involve the use of chemical reagents, this method tends to have a lower environmental impact compared to conventional chemical treatments. Moreover, fiber length is a key factor influencing the final performance of the composite. Nevertheless, few studies have explored hornification effects on mixed jute and mallow fibers and the influence of fiber length on composite properties. This study investigated the impact of hornification and fiber length on the physical, thermal, and mechanical properties of polypropylene (PP) waste composites reinforced with jute and mallow fibers. Fibers were treated by hornification and characterized regarding physical, thermal, chemical, and structural properties. Composites with treated and untreated fibers of lengths 1, 1.5, and 4 cm were produced and evaluated by Izod impact testing, thermal conductivity, swelling, water absorption, and density. Hornification reduced fiber moisture content from (12.47% ± 1.60%) to (9.73% ± 0.41%) and extractives from (10.13% ± 2.09%) to (1.25% ± 0.01%), indicating a significant reduction in hydroxyl groups and water uptake. Among fiber lengths tested, 1.5 cm fibers showed the best performance in water absorption and swelling. Results confirm that both hornification and fiber length significantly influence the composites' physical properties.