Research On Manufacturing And Properties Of Wood/Rubber/HDPE Composites

Wood/waste rubber/HDPE composite(WRPC) is a brand new kind of wood-based multiple composite material. The raw materials function differently in the composite system, wood fiber is the reinforcing phase acting as "skeleton", rubber plays well damped cushion effect, while the plastic matrix function as the "adhesive" component. In this study, WRPCs were made by extrusion molding method, and systematic research related to mixing ratio, interface modification and the evaluation of the effect of rubber toughening modification has been carried out to set a theoretical foundation for the preparation of ternary composites.The results were shown as follows:1. The mixing ratio of the three raw materials significantly affects the mechanical properties of the composite. The addition of rubber has improved the impact strength of the material, while the tensile strength and flexural strength(MOR) were weakened. Complementary effect on mechanical properties has been observed between wood flour and waste rubber. To obtain a certain strength, while ensuring the molding process, wood flour content of the composite should be more than 30%, and no less than 4/6 ratio of HDPE to rubber is required.2. Toughening effect of the rubber showed that, with untreated rubber adding to WPC, 10% dosage exhibited good compression resilience, and the impact strength increased with increasing amount of rubber in the range of 0-15%.Meanwhile,optimal damping properties were observed when 10% rubber was added, the damping ratio of which has increased by 67% compared with pure WPC(Time-domain method).3. Maleic anhydride grafted polyethylene(MAPE) and silane(Si69) coupling agent were used to improve the interfacial bonding of the composite. The adding amount of MAPE was 3%、5% and 8%,for Si69, it was 0.5%、1%、3%、and 5%. FT-IR analysis showed that if treating the rubber particles with different content of silane coupling agent, the number of hydroxyl groups increased, indicating that the surface polarity has been enhanced. Effects of the two coupling agents on the rheological properties of the composite showed a trend of polarization. with 5%MAPE adding content, the composite showed minimum values of shear stress and apparent viscosity, which means an optimal processing performance. As to the silane coupling agent,3% amount is the best. Mechanical properties were improved with the use of the two kinds of coupling agent, and good synergy effect was observed. In addition, the higher the MAPE dosage, the better the mechanical properties. Complementary effect should be taken into accout in determining the amount of silane coupling agent. Mechanical properties of the composites increased with increasing amount of Si69 in the range of 0.5%-5% when there is a low adding amount of MAPE, on the contrary, with high MAPE use, the proper amount of Si69 is 0.5% when considering the mechanical properties as well as the convenience of the modification treatment.4. Xenon arc lamp ageing results showed that, within 0-480 h aging time, flexural strength(MOR) of the composites firstly decreased and then increased, then became lower and lower at last. Rubber changed the aging process of the composites, but did not accelerate the aging process. Coupling agent MAPE and Si69 can improve the aging resistance of the composite materials, which was mainly reflected in residual strength in the latter part aging.5. Thermogravimetric analysis(TGA) method was applied to investigate the thermal decomposition kinetics of wood flour, HDPE, waste rubber, WPC, and WRPC. The corresponding apparent activation energy(AAE) values were calculated with the Flynn-Wall-Ozawa model. The results showed that WRPCs have two weight loss stages at 230~380 ℃ and 430~580 ℃ due to thermal decomposition of wood/rubber and HDPE, respectively. The AAE values for wood, waste rubber, HDPE are 179.2KJ/mol、243.8KJ/mol, and 246.8KJ/mol, respectively, while 239.3KJ/mol for WPC. Decreased AAE values were found for WRPCs, i.e., 200.3~208.4 KJ/mol. It is then concluded that the three raw materials, i.e., wood, rubber, and HDPE, synergistically react in WRPC decomposition process, and rubber addition content has evident influence on the thermal decomposition behaviors of WRPC.6. Combustion degradation characteristics parameters such as thermal stability time to ignition(TTI), heat release rate(HRR), total heat release(THR), mass loss rate(MLR), total smoke production(TSP), and release of CO and CO2 were tested using cone calorimeter. The results showed that WRPC had shorter TTI, lower CO2 release, and higher HRR, THR and TSP values compared with that of wood-plastics composites. Waste WRPC could be recycled as an excellent fuel, and waste rubber may promote the combustion of WRPC.