Interfacial bonding properties of multi-phase co-extruded wood-plastic composites

To address the problems of low interfacial bonding strength between sub-surface wood-plastic composites (WPCs) and solid wood in the core layer of new multi-phase co-extruded composites and easy interfacial peeling in the process of use leading to the reduction of the mechanical properties and service life of the composites, this paper adopts a polyurethane hot-melt adhesive film (TPU) and an ethylene acrylic acid copolymer adhesive film (EAA) to wrap veneer laminated lumber (LVL) with plastic/wood-plastic. Multi-co-extruded composites (Co-WPCs-LVL) with high interfacial bond strength were prepared. The results showed that both TPU and EAA could effectively improve the interfacial bonding strength between WPCs layer and core layer LVL, and the interfacial bonding strength decreased gradually with the increase of the melting point of the adhesive film, among which, the interfacial bonding strength between WPCs and LVL introduced with TPU (melting point of 80℃) and EAA (melting point of 95℃) was increased by 27 and 56 times, respectively, relative to that of the untreated group. The EAA could significantly increase the interfacial bonding strength of the water resistance of the interface between WPCs and LVL, and the interface did not peel off after the Type II impregnation experiment. It proves that the adhesive film can penetrate into the surface of LVL and react with hydroxyl group (-OH) under the extrusion at high temperature, and at the same time, it can mix and diffuse with the molecular chain of polyethylene to form a strong interfacial bond. After artificially accelerated aging, the WPCs and LVL in the adhesive film treatment group still had high interfacial bonding strength, and the residual rate of interfacial bonding strength increased with the increase of melting point, among which the experimental group of EAA (melting point of 135℃) showed the best interfacial durability, and the residual rate of interfacial bonding strength reached 97.25%.