Extrusion Hot water extraction Hygroscopicity Wood plastic composites (WPC)
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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.