Effect of acetylated wood flour or coupling agent on moisture, UV, and biological resistance of extruded woodfiber-plastic composites

Abstract

Although moisture sorption in woodfiber-thermoplastic composites (WPCs) is slower than in unmodified solid wood, it still affects strength and ultimately results in decay of the material in moist outdoor exposure conditions. Chemical modification of the hydroxyl groups of wood with acetic anhydride esterifies the hydroxyl making the wood more hydrophobic and dimensionally stable. Coupling agents are known to promote bonding between the plastic and unmodified wood fibers when added to WPCs. The objective of this study was to investigate several methods of decreasing moisture sorption and, consequently, fungal degradation in WPCs. Three WPC blends were extruded into 3-by 12-by 90-mm specimens: 1. 50 percent high-density polyethylene (HDPE) and 50 percent western pine wood flour (WF); 2. 47 percent HDPE, 3 percent coupling agent (maleated polyethylene [MAPE]), and 50 percent WF; and 3. 50 percent HDPE and 50 percent acetylated WF. In addition, a stearate lubricant was used in all three blends to aid processing. Specimens were preconditioned before running a modified ASTM D 1413 soil block test either by 2-week water soaking or 1,000 hour exposure in an ultraviolet weatherometer and then 2-week water soaking. Acetylation of the wood fiber decreased moisture content and fungal decay compared with unmodified WPC controls. Mechanical properties decreased initially in composites containing acetylated WF but were not further affected by preconditioning or decay compared with unmodified WPC controls.

Citation

Ibach, Rebecca E.; Clemons, Craig M. 2006. Effect of acetylated wood flour or coupling agent on moisture, UV, and biological resistance of extruded woodfiber-plastic composites. Wood protection 2006 : March 21-23, 2006 ... New Orleans, Louisiana, USA. Madison, WI : Forest Products Society, 2006: Pages 139-147