Studies on polymer-wood interface bonding: Effect of coupling agents and surface modification

Mechanical properties of composites are a direct function of the interface bonding between strengthening fiber and the matrix. This study investigates the influence of surface modification of wood chips and presence of different interface coupling agents on the interface bonding of wood-polyethylene composites. Single wood-polyethylene interfaced samples were prepared by introducing extruded polyethylene from a twin extruder to bond to the rip surface of a rod-shaped wood specimen. Sodium hydroxide and sulfuric acid were used as surface modifiers for wood. The bond-modifying properties of three silane coupling agents were investigated. The coupling agents used were vinyltrimethoxysilane, 98%, 3-(trimethoxysilyl)propylmethacrylate, 97%, and 3-glycidoxypropyltrimethoxy silane, 96%. Direct measurement of the interfacial bond strength was carried out using an Instron tensile test machine. Individually, the acidic modifier showed adverse effect on the interface. However, sodium hydroxide improved the interface bonding and enhanced the bond strength by a factor of 1.3 to 1.5. Basically, all of the coupling agents individually increased the interface bonding; vinyltrimethoxysilane, (H2C=CHSi(OCH3)(3)), had the greatest effect. Also, surface modifiers and coupling agents applied together showed a synergistic effect which contributed to an improved polymer/woodstock interface bond.