Extrusion Hot water extraction Hygroscopicity Wood plastic composites (WPC)
Undebarked ponderosa pine chips were treated by hot water extraction to modify the chemical composition. In the treated pine (TP), the mass was reduced by approximately 20 %, and the extract was composed mainly of degradation products of hemicelluloses. Wood flour produced from TP and unextracted chips (untreated pine, UP) was blended with high-density polyethylene (HDPE) and polypropylene (PP) and was extruded into wood plastic composites (WPCs). Formulations for WPCs consisted of 58 % pine, 32 % plastic, and 10 % other additives. WPC based on HDPE? + ?TP and PP? +?TP absorbed 46-45% less water than did WPC based on HDPE? +?UP and PP? + ?UP, respectively. Thickness swelling was reduced by 45-59%, respectively, after 2520 h of immersion. The diffusion constant decreased by approximately 36 %. Evaluation of mechanical properties in flexure and tension mode indicated improvements in TP-WPC properties, although the data were not statistically significant in all cases. Results showed that debarking of ponderosa pine is not required for WPC production.