Recycling performance of Pennisetum setaceum Fiber/HDPE composites: a study on mechanical and thermal behavior

• Up to five recycling cycles feasible for P. setaceum fiber–HDPE composites • Alkaline-treated fibers enhance HDPE crystallization behavior after recycling test • Eco-friendly P. setaceum composites show promise for circular use • HDPE showed a 71.2% MFR increase after 5 cycles, higher than that of the composites Plant fiber-reinforced composites offer a pathway to more biodegradable materials but recycling these composites before disposal presents a more environmentally sound strategy. This study investigated the recyclability of composites made from virgin and recycled high-density polyethylene (HDPE) matrices, reinforced with Pennisetum setaceum fibers, both untreated and alkaline treated. After five recycling cycles, notable trends emerged. Specifically, tensile strength and elastic modulus significantly increased in composites with 20% and 40% fiber loadings. Flexural strength, however, generally declined in recycled HDPE composites, while remaining stable in virgin HDPE composites. Melt Flow Index (MFI) analysis showed enhanced material fluidity in composites with untreated fibers post-recycling. Furthermore, Differential Scanning Calorimetry (DSC) indicated that alkaline-treated fibers promoted polymer crystallization during recycling. These findings suggest that alkaline treatment enables P. setaceum fibers to maintain structural integrity across multiple recycling cycles, thereby enhancing the overall recyclability of the composite.