| Wood-plastic composite (WPC) is a new type of green environmental friendly material in recent years, it has advantages of both wood and plastic, can replace the wood and be used in construction, packaging, automotive industry, furniture and other fields. When composite is used in damp environment or outdoors such as park, pavilions for a long time, it may still be affected by the violation of the mould and wood rotting fungi on its aesthetics, seriously affects its service life, therefore, manufacturing enterprises urgently want to solve the problem that how to improve fungi and mould resistance of WPC. In this paper, processing sawdusts of Pinus massoniana and Cunninghamia lanceolata were choiced as fillers, and modified by high-temperature heat treatment, then were made into wood-plastic composites with high density polyethylene (HDPE). The effect of heat treatments on decay resistance, mold resistance, mechanical properties and water absorption was investigated. The chemical composition and surface microstructure of composites before or after the decay test were characterized by Fourier transform infrared (FTIR) and scanning electron microscope (SEM), the main conclusions obtained from above research are as follows:(1) In N2medium, the mass losses of Pinus massoniana wood flour and Cunninghamia lanceolata wood flour with treatment at180,200and220℃and processing time for1,2and3h respectively were increased in varying degrees. But when the processing temperature was under200℃, the mass losses of two wood flours were not obviously different in general with the processing time was lengthened, the former was between0.76%and1.38%, the latter was between0.84%and1.15%. When the processing temperature was220℃, the mass losses of two wood flours were increased slightly, and the mass losses of two kind wood flours treated with this temperature for3h were2.18%and1.96%respectively. FTIR analysis showed that the stretching vibration strength of two kind wood flours near the3426cm-1(O-H),2922cm-1(C-H),1737cm-1(C=O) and1056cm-1(C-O) as it weakened gradually with processing temperature increased and time lengthened. (2) Compared with untreated control samples, Pinus massoniana wood flour and Cunninghamia lanceolata wood flour treated with different heat treatments had contributed to composites for lowing the water absorbing rate and thickness swelling rate in varying degrees, and with processing temperature increased and time lengthened the reduction was obvious, especially the two wood flours heat-treated at220℃for3h, the water absorbing rate of composites were reduced by37.18%and33.55%, the thickness swelling rate of composites were reduced by30.68%and30.97%respectively. And in the same heat treatment, the water absorption of Cunninghamia lanceolata wood flour/HDPE composites were slightly lower than that of Pinus massoniana wood flour/HDPE composites.(3) Compared with untreated control samples, Pinus massoniana wood flour with processing temperature increased and time lengthened had less effect on its composites’tensile strength, impact strength, and flexural properties. For Cunninghamia lanceolata wood flour/HDPE composites, the change of mechanical properties of composites was also little when wood flour was heat-treated under200℃for different time. But when it was treated at220℃with the processing time was lengthened, composites’tensile strength, flexural strength, and impact strength were significantly lower, especially mechanical properties of composites whose wood flours were treated for3h had the most reduction, decreased by12.85%,8.31%and34.85%, respectively. While SEM images of fractured surfaces of tensile test sample of composites revealed that the change of interfacial adhesion of wood flour and HDPE also reflected the change of mechanical properties.(4) Compared with untreated control samples, whether heat-treated Pinus massoniana wood flour/HDPE composites or heat-treated Cunninghamia lanceolata wood flour/HDPE composites were infected by brown-rot fungus and white-rot fungus12weeks respectively, their average mass losses both had a decrease in varying degrees, but the decline was not obvious. It was concluded that the two composites after brown-rot fungus with wood flours treated for3h at200℃and220℃had the least mass loss, and composites after white-rot fungus with wood flours treated for3h at220℃had the least mass loss. And the mass loss of the latter was slightly smaller than that of the former with same heat treatments.(5) The FTIR analysis showed that each composite after rot test had no obvious change in the position of characteristic peak and the height of relative peak, and also did not appeared new characteristic peak. SEM analysis revealed that the surface of untreated control samples after rot test were found the existence of the hyphae, however, on the surface of heat-treated wood four/HDPE composites were less seen or found no hyphae, then it showed that wood flours after heat treatments could improve the decay resistance of wood-plastic composites to a certain extent.(6) The surface of two kind wood flours untreated control samples infected by mould had a damaged degree of4, which were easily infected by mold, however, damaged degrees of composites whose wood flours were heat-treated with different treatments after mold disoperation had been decreased between0-3, two composites had the least infected mold area when two kind wood flours were treated at200℃for3h, the value was2.50%and9.75%, and the damaged degree was0and1, respectively. Composites with the two wood flours after heat-treatment had the same effect on the mold resistance. |
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