Formulation and process development of flat-pressed wood-polyethylene composites
2003
Wolcott, Michael P.
Wood-plastic composites have emerged primarily in response to the need for moisture-durable wood-based materials. Although a great deal of research has addressed extruded composites and formulations, little work has addressed the use of thermoplastics to modify conventional particulate wood composites. This research is aimed at determining processing and performance behavior of dry-blended wood-HDPE (high-density polyethylene) formulations using conventional hot-pressing techniques. Thermal analysis of the individual and blended components was used to guide the development of pressing schedules. Both the amount and melt flow index (MFI) of the HDPE used were found to significantly influence the flexural behavior of the pressed panels. Both panel MOR and MOE were improved with decreased levels of HDPE and low MFI values. However, only HDPE content effectively lowered moisture absorption, thickness swelling, or the swelling coefficient. In contrast to the mechanical behavior, all moisture properties measured were enhanced by increasing the HDPE content of the formulations. The use of wax and zinc stearate in the formulation decreased panel MOR while enhancing moisture resistance. The strong decrease in panel strength combined with no influence of panel stiffness of these lubricants strongly suggests that the lubricants are preferentially located on or near the wood surface. This conclusion is consistent with the increased moisture resistance afforded by these additives.
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