Correlation between physical bonding and mechanical properties of wood-plastic composites: part 2: effect of thermodynamic factors on interfacial bonding at wood-polymer interface

The main objective of this study was to find out if there is any significant correlation between physical properties and interfacial bonding of interphases in wood-plastic composites. To this end, high-density polyethylene (HDPE), mixture of 3% maleic anhydride grafted polyethylene (MAPE) and HDPE (coded as MHDPE) and polylactic acid (PLA) were separately interacted with veneers to identify factors underlying interfaces. Plastics were first melted at 180 degrees C and dispensed on wood surfaces so that the contact angle (CA) could be directly measured. Wood sanding moderately decreased the CAs of plastics in order of PLA, MHDPE, and HDPE. The treatment of veneers with MAPE comprehensively improved wetting, as the CA of HDPE was significantly reduced on the wood surface after the treatment. Thereafter, the interfacial shear strengths (IFSS) of the wood-polymer interface were determined using the automated bonding evaluation system. PLA had the highest IFSS both for unsanded and sanded veneers. Comparing both parts of this research finally revealed that applying sanding or/and MAPE treatments resulted in lower surface free energy and higher IFSS at the wood-polymer interface. However, our observations support the idea that, at higher temperatures, wetting of composites is mainly influenced by polymer properties rather than interfacial tension at the wood-polymer interface.