| Wood plastic composites (WPC), made from various plastics and biomaterials as reinforced materials, are a new type of green environmental composites with high performance and added value. However, due to the poor interfacial compatibility between the polar biomaterials and the nonpolar plastics matrix, the interfacial bonding between the two components is not effective, and it can't make full use of the fiber strength, which in turn influence the performance of composites. Therefore, to improve the interfacial compatibility and enhance the interfacial bonding between biomaterial and plastics are key points for evaluating the performance of the composite. In this paper, poplar wood fibers were modified with six kinds of representative silane coupling agents (A-151, A-171, DB-550, DB-560, DB-570 and DB-580, respectively) with different molecule structure, then blended with high density polyethylene (HDPE) to prepare composites by extrusion. The most effective silane coupling agent was selected out by comparing the mechanical performances and water resistance properties, and analyzing the morphology of the fracture surface, FTIR spectra and rheological properties of the composites. Then optimized the modification technology of this best silane coupling agent, included the amount and solution concentration of the silane and the amount of dicumyl peroxide (DCP), which used as free radical initiator.Compared to the untreated wood flour/HDPE composite, the mechanical properties and water resistance were all improved after treated with the six different silane coupling agents, and A-171 was the most effective. The observation of scanning electron microscope (SEM) indicated that the morphology of the fracture surface of the composites after treated was changed and the interfacial bonding between wood flour and matrix was reinforced, the interfacial compatibility of the two phases was effective improved. Compared to the FTIR. spectra of untreated wood flour, there was a new characteristic absorption peak at 770cm-1 belongs to Si-O-Si bond generated by self-polymerization of silanol and a reinforced one at 1108cm-1 belongs to the covalent bond Si-O-C after treated with A-171, which indicated the possible polycondensation grafting reaction between A-171 and wood flour.The mechanical strength and water resistance of the composites were all increased with increasing the amount of DCP and A-171. When the amount of DCP was 0.13% and A-171 was 4%, the flexural and tensile strength and water resistance were all maximum. Continue to increase the amount of DCP, the mechanical strength and water resistance were begin to decrease, which may attributed to the HDPE degradation caused by higher amount of DCP. When the amount of A-171 was exceeded 4%, the increasing extent of flexural and tensile strength of the composites was smaller with the increase of the amount of A-171, but the impact strength increasing obviously until the amount of A-171 exceeded 6% The solution concentration of A-171 had slight effects on mechanical properties of composites, but the water resistance of composites was decreased with the increase of solution concentration of A-171.Rheology study indicated that different kinds of silane coupling agents and different amount of A-171 had little effect on the linear viscoelastic regions (LVR), but the storage modulus G' of composites was decreased with the increasing of strain amplitude, exhibited nonlinear viscoelastic properties. The G' and viscosityη*of the composites treated with different kinds of silane coupling agents and different amount of A-171 were decreased compared to the untreated wood flour/HDPE composite, but the loss tangent tan8 of the treated wood flour/HDPE composites were all increased with little difference. The viscosity of the composites was continuously decreased with the increase of frequency, showed the shear thinning behavior. |
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