Stress relaxation behavior and effects of accelerated weathering on properties of silane-treated rubberwood/recycled polypropylene wood-plastic composites

Silane-treated rubberwood flour (RWF) was mixed with recycled polypropylene (rPP) at the optimum proportions of 39.22 wt% RWF content and 60.78 wt% rPP, with the RWF being silane-treated at a 3.44% concentration based on the weight of RWF. These materials were mixed to produce wood-plastic composites (WPCs) using twin-screw extrusion followed by hot pressing. The objective of this study was to investigate the stress relaxation behavior and the effect of accelerated weathering on the mechanical properties of the produced WPCs. The results show that stress relaxations at different temperatures with constant strain levels were consistent, and the stress decreased with time. In addition, the stress relaxation rate increased with strain level at a constant temperature. Time-temperature superposition was applied to construct a master curve extension for 1.0, 1.5, and 2.0% strain levels over 208, 187, and 75 days, respectively. The results indicate that the WPCs were rheologically simple materials, and a single horizontal shift of the time axis was adequate to predict their long-term responses. Moreover, accelerated weathering tests of the WPCs indicate that accelerated weathering had no significant effect on the mechanical properties of WPCs.