| Two studies were used to assess the durability of wood-plastic composites (WPCs) exposed to accelerated freeze-thaw cycling. A counter-rotating twin-screw extruder was used to process various formulations of WPCs, which were then exposed to accelerated freeze-thaw testing according to ASTM standard D-6662. This method includes exposure to water submersion, freezing, and thawing as one complete cycle. The effects of 2 to 15 freeze-thaw cycles were observed for the density, dimensional stability, flexural strength and stiffness, porosity, and microscopic appearance of WPCs containing both maple and pine wood flour. Of the composite formulations tested with varied wood contents, only the lower wood content WPCs showed resistance to freeze-thaw actions. The density of all WPCs were unaffected by freeze-thaw actions. The WPCs maintained relatively stable dimensions after exposure compared to other materials such as solid wood. The flexural strength and stiffness of all WPCs were significantly decreased by as few as 2 cycles. Scanning electron microscopy confirmed similarities between water-only and full freeze-thaw cycles. The main cause of the flexural property losses was attributed to the water portion of this cyclic process, which led to decreased bonding between the wood and polymer, which also increased the porosity. The freezing (without water) had a lesser effect on WPCs compared to the water portion. |
