Evaluation of Flexural Strength (MOR) and Stiffness (MOE) in Wood–Plastic Composites (WPC) Made from Recycled HDPE and Pine Sawdust

Abstract

This study evaluated the mechanical behavior of wood–plastic composites (WPC) manufactured from recycled high-density polyethylene (HDPE) and pine sawdust. A 22 factorial design was applied to analyze the influence of extrusion temperature (185 °C and 195 °C) and sawdust content (10 % and 20 %) on the mechanical properties. Twenty specimens were tested under three-point bending according to ASTM D790 to determine the modulus of rupture (MOR) and modulus of elasticity (MOE). The analysis of variance (ANOVA) revealed that both factors exerted a statistically significant influence (p < 0.01), with sawdust content being the dominant factor showing high effect sizes (η2 = 0.82 for MOR and 0.65 for MOE). Increases in sawdust content and temperature reduced strength and stiffness by an average of −2.8 MPa and −210 MPa, respectively, due to interfacial adhesion loss and thermal degradation of lignocellulosic fibers. The optimal condition of 185 °C and 10 % sawdust achieved the maximum strength (28.46 ± 0.65 MPa) and stiffness (1849.1 ± 72.1 MPa), highlighting the potential of recycled WPCs for lightweight structural applications.