The Enhancement Mechanism And Interfacial Compatibility Of Wood-plastic Composites

Wood plastic composites, which are widely used in outdoor patio and construction due to their excellent performance, are green and recyclable materials. However, the use of wood plastic composites is limited because of the interface compatibility, antistatic properties, and heat resistance of the wood plastic composites are poor. In order to improve those problems, the wood fibers were treated by different chemical modification, the effects of different modification methods on the mechanical strength, dimensional stability of wood plastic composites were investigated. And the interfacial modification mechanism was analyzed by fourier transform infrared (FTIR) and scanning electron microscopy (SEM). Moreover, the minerals and conductive fillers were added into the wood plastic composites matrix, the influence of fillers on the mechanical strength, heat resistance and anti-static properties of wood plastic composites were investigated, and their reinforcement mechanism were analyzed by scanning electron microscopy and energy spectrum (SEM-EDS) and x-ray diffraction (XRD). The main results are as follows:(1) Effect of esterification on the properties of wood plastic compositesThe surface hydrophobicity of the wood fibers could be improved effectively and their configuration and micromorphology could be changed by controlling the extent of esterification in order to increase the interfacial bonding strength of the wood plastic composites. After the birch wood powder treated by acetic anhydride solution, the polarity of the wood fibers was reduced due to the hydroxyl groups partly replaced by the acetyl groups and the length and wall thickness of wood fibers became increasing. Moreover, the surface of the wood fibers treated became smoother and the wood plastic composites became more dense.(2) Effect of xylanase solution on the properties of wood plastic compositesThe interfacial bonding of wood plastic composites were enhanced after xylanase solution. After the wood fibers were treated in a xylanase solution of concentration 800IU·g-1 under the conditions of a temperature of 40℃ and a pH of 4.5 during 2h, the relative content and crystallinity of cellulose and the relative content of lignin increased in the betula alnoides wood fibers, while the relative content of hemicellulose decreased. The comprehensive mechanical properties of the composites were enhanced due to the increased interface aera between plastic and treated wood fibers whose surface became softer and rougher.(3) Effect of silane coupling agent on the properties of wood plastic compositesThe interfacial bonding of wood plastic composites were enhanced after treated by silane coupling agent. After the wood fibers were treated in a silane solution of concentration 4wt%, the mechanical property and dimensional stability of the wood plastic composite reached best due to the bridge formed between plastic and treated wood fibers whose surface occurred condensation grafting reaction.(4) Effect of bauxite on the properties of wood plastic compositesThe mechanical strength and the heat resistance and the wear resistance of wood plastic composites are improved by adding the appropriate content of bauxite. When bauxite is added into wood plastic composites, it can be evenly distributed in composites matrix and the degree of crystallization of wood plastic composites are improved in order to bear the load effectively and reduce the deformation of the composites under stress caused by external or destruction. However, the mechanical strength and the heat resistance and the wear resistance decrease and the coefficient of linear thermal expansion of the composites increase due to the bauxite are unevenly distributed and formed agglomeration easily when the content of bauxite is too high.(5) Effect of flake graphite on the properties of wood plastic compositesThe influence of the flake graphite (FG) content on the mechanical properties. triboelectrification electrostatic potential, and electrical resistivity of the wood plastic composites were investigated. The mechanical strength of the composites decreased with increase in the FG mass fraction. When FG was added into the wood plastic composites, the composites were readily deformed or damaged under the external load because of stress concentration and slippage of the interfacial layer in the composites. The triboelectrification electrostatic potential of the wood plastic composites was<10 V and the electrical resistivity of the composites reached an anti-triboelectrification threshold because of the formation of conductive paths. However, when the FG mass fraction was less than the anti-triboelectrification threshold, the triboelectrification electrostatic potential of the wood plastic composites reduced in the order oxygen> nitrogen> air> argon> vacuum because the ionization or activation of the gas molecules contributed to the improvement of the triboelectrification electrostatic potential of the composites.