| The surface of wood/polyethylene (PE) composites was treated by liquid chemical oxidation to improve its adhesion properties. And the surface properties changes of liquid oxidation treated wood/polyethylene composites and the durability for bonding joint of wood/polyethylene composites under the environment of normal temperature (23℃) soaking, high temperature (80℃) soaking,80℃heating, ultraviolet aging and natural aging were studied through both micro structure and macro properties by using the analysis of contact angle, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and compression shearing strength test.Wood/polyethylene composites was treated by liquid chemical oxidation, and the results showed that the roughness of surface for liquid oxidation treated polyethylene wood-plastic composites increased, the polar oxygen-containing groups of C-O, C=O and-COOH were introduced on the composites surface, the relative content of carbon element within the surface of composites decreased and the relative content of oxygen element increased, and the value of O/C increased, which induced the bonding strength improved significantly, and the failure mode of bonding joints was the body destruction of bonded composites. The test results of soaking experiment showed that, with the soaking time prolonging, the aging crack on the composites surface increased gradually, the more obviously roughness lead to contact angle decreased, the relative content of carbon element within the composites surface decreased and the relative content of oxygen element increased, the value of O/C increased. Although the bonding strength decreased after soaking, the failure mode of bonding joints was still the body destruction of bonded composites; and rising water temperature could make wood-plastic composites surface aging exacerbated and bonding joints strength reduced severely, when the bonding joints destructed, the body destruction of bonded composites was more severe, which related to the moisture absorption and expansion of the wood fiber within the wood-plastic composites. The test results for heating aging experiment showed that after heating, grooves and pores of composites surface reduced, which induced surface roughness reduced and the contact angle enlarged, the relative content of carbon element within the composites surface increased and the relative content of oxygen element decreased, the value of O/C decreased. And the heating for a long time would make the composites surface aging, and the surface properties progressed oppositely. After heating aging, the bonding strength showed a decreasing trend, but the failure mode of bonding joints was the body destruction of bonded composites yet. The test results for UV aging experiment indicated that the aging crack was formed on the composites surface after UV irradiation, which made the composites structural strength reduced and caused the bonding strength decreased, and the results for UV aging experiment indirectly confirmed that UV irradiation would have an effect on the bonding joint for liquid oxidation treated wood-plastic composites. The test results for natural aging experiment showed that when the bonding joints suffered by light, temperature and humidity together, the bonding performance of the bonding joints declined, however, the bonding joint for liquid oxidation treated wood-plastic composites could still maintain a relatively high bonding strength, and the failure mode of bonding joints was all the body destruction of bonded composites. The mentioned above indicated that liquid phase oxidation treatment could increase the bonding strength of polyethylene wood-plastic composites and improve the durability of wood-plastic composites bonding joint. |
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