Preparation And Aging Properties Of The Colorful Wood Plastic Composites

Wood plastic composites (WPC), which have the double peculiarities of plastic and wood fibers, are environmentally friendly composites. At present, WPC is widely used in construction, decoration, and automobile interiors. However, WPC is often used in the environment of light, rain and fungal erosion, which may decrease the mechanical properties of composites and cause the surface discoloration of composites. Moreover, the environment could affect the normal use of the composites and shorten its using life. In order to improve the single color and poor anti-aging properties of the birch wood flour/ high density polyethylene (HDPE) composites, which were prepared by using the hot-pressing technology in a vulcanizing machine. The effects of colorant type and content on the mechanical strength and surfuce color of wood plastic composites were investigated. Moreover, the wood plastic composites were treated by the methods of outdoor natural aging and UV accelerated aging. The surface chemical functional groups before and after aging were analysed by the Fourier transform infrared spectroscopy (FTIR), while the aging mechanism of the wood plastic composites were concluded by the changes of the surface morphology, mechanical properties, and the surface color before and after aging.The results showed that:(1) Effect of the color agent on the mechanical properties and surface color of wood plastic compositesThe mechanical properties and surface color of the wood plastic composites changed significantly filled with the different organic or inorganic color agent. The chromaticity values of the composites, such as the brightness value (L*), red-green value (a*), yellow-blue value (b*), increased with the increaing color agent, and the total color value (ΔE*) and the mechanical properties of the composites increased with the the increaing color agent. When the colorant amount was 3.5wt%, the mechanical properties and surface color reached to the best.(2) Effect of the UV accelerated aging on the mechanical properties and surface color of wood plastic compositesThe mechanical properties and surface color of the wood plastic composites changed significantly after UV accelerated aging. The mechanical properties of the composites decreased and the composites faded seriously with the increaing aging time. However, the surface faded and the mechanical strength decreased by the addtion of the organic or inorganic colorant, which indicated that the color agent could improve anti-aging properties of the composites by retarding the fading and the mechanical strength reducation of the wood plastic composites. The chromophore was generated on the composites surface and the color agent and a lot of wood fibers were washed away from the surface of the composites. Moreover, the comprehensive performance of the composites deceased due to the black spots and surface cracks.(3) Effect of the outdoor aging on the mechanical properties and surface color of wood plastic compositesThe comprehensive performance of the wood plastic composites decreased after the three months outdoor natural aging. The mechanical properties of the composites decreased and the composites faded seriously with the increaing aging time. However, the anti-aging properties of the composites were improved by adding the color agent. The surface of composites occured photodegradation reactions, while the color agent and a lot of wood fibers were washed away from the composites surface. Moreover, when the external force was applied on the composites, it may be easily deformed or damaged due to the reducation of the bonding strengh.(4) The properties before and after UV accelerated aging and outdoor natural aging results showed the composites under outdoor conditions fading seriously, and the mechanical strength decreased greatly. The anti-aging properties of the composites added with inorganic titanium dioxide color agent were better than the composites added with organic color agents.