Durability of an extruded HDPE/wood composite

As a part of wood-plastic composite (WPC) material development, this research evaluated the resistance of WPC formulations to fungal decay and biocide leaching. In laboratory tests using small WPC samples exposed directly to brown-rot and white-rot fungi, there were no weight losses caused by decay in most formulations. Formulations with relatively high wood content and not protected by zinc borate exhibited moderate weight losses. Results indicate that either the inclusion of zinc borate or limiting the wood content of WPC can effectively prevent fungal decay. The very low leach rate as determined by laboratory testing appears to be controlled mainly by dissolution of the zinc borate and not by diffusion. The tests show that zinc borate will take at least 20 years to completely dissolve and leach from the material. Results indicate that careful material design can prevent fungal decay of WPC even under severe exposures.