Sustainable High-Density Polyethylene Composites Reinforced with Olive Pomace: Production and Characterization

In this study, olive pomace (OP), an abundant agro-industrial by-product, was incorporated into a high-density polyethylene (HDPE) matrix at loadings of 0–20 wt.% to develop sustainable polymer composites. The influence of OP loading on the physical, mechanical, structural, and thermal properties of the composites was systematically investigated. Increasing OP loading resulted in elevated moisture content and water absorption, attributed to the hydrophilic nature of the lignocellulosic filler. Composite density and Shore D hardness exhibited a progressive increase with OP loading. In contrast, tensile and impact properties remained statistically not significantly changed at 5 wt.% OP loading, while higher filler loadings (10–20 wt.%) resulted a significant decrease in mechanical performance, accompanied by a transition from ductile to more brittle fracture behavior. Fourier-transform infrared spectroscopy (FTIR) analysis indicated a decrease in the intensity of characteristic HDPE bands and partial disruption of polymer crystallinity, suggesting predominantly physical interactions between the matrix and filler. Thermogravimetric analysis (TGA) revealed a decrease in the onset degradation temperature with OP addition; however, enhanced char formation contributed to improved thermal stability at higher degradation stages. Overall, the findings suggest that OP is more suitable for use in HDPE composites at relatively low filler loadings.