UV Accelerate Degradation Of Rice-hull/HDPE Composites

Wood plastic composites are often used outdoor. Its resistance to weathering is concerned. This paper focuses on evaluating the properties of Rice-hull/HDPE (RH/HDPE) composites after exposed to accelerated UV-weathering. RH/HDPE composites with different rice hull content was weathered under the artificial accelerated UV-weathering test conditions.The configuration of the composite surfaces were observed and analyzed with scanning electron microscope, and then the performance of composites and surface chemical changes after the aging were evaluated by static mechanics test, color difference analysis, Fourier transform infrared (FTIR) spectrum analysis, and X-ray photoelectron. The relationship between components in RH/HDPE composites and the weathering resistant quality of composite were analyzed, and then the effect of ultraviolet absorbers, inorganic pigments, a resistance amine light stabilizer, and other light stabilizers was investigated. In the meanwhile, synergistic effect of different light stabilizer was discussed. Eventually the formula that resist to UV weathering was confirmed. This research would provide theoretical foundation for improving wood and plastic composites'weathering resistance, and establish a process for evaluate the application of wood plastic composites. The main research conclusions are as follows:(1) In the process of UV-weathering, the lightness (L*) of all samples increased, however,. L*of RH/HDPE composites varied in a larger margin than pure HDPE. In the first250h of exposing, L*changed most. In the meanwhile, surface cracks came into being and bending performance decreased. With the increase of rice-hull powder content and UV weathering time, L*continuously increased, i.e. samples faded aggravatingly, and surface crack became more serious, flexural property decreased and surface oxidation increased also.(2) Surface chemical variation of pure HDPE and RH/HDPE composite material before and after UV-weathering was analyzed with FTIR. The addition of rice-hull powder to HDPE introduced more carbonyl, which resulted in more carbonyl index presented in RH/HDPE composites sample. In the process of UV-weathering, HDPE molecule chains break, the carbonyl index of RH/HDPE composites surface increased significantly. Chain cession and crosslinking happened simultaneously. These made the crystallinity of HDPE change.(3) Cellulose index and lignin index of RH/HDPE composites increased with the increasing of rice-hull powder content. During UV-weathering, the loss of cellulose index and lignin index increased. at the end2000h UV-weathering, the lignin index of composite materials with different rice-hull powder content decreased to lowest value, and there was no significant differences among each other. Analysis indicated that lignin is very sensitive to ultraviolet light, and almost degraded completely. (4) Ultraviolet absorber agent and pigment reduced fade and crack on the surface of RH/HDPE composites, reduced the loss of bending performance, and delayed the occurrence of oxidation in composites. UV-326reacted better than UV-531, and carbon black is the best pigment to protect composites. Resistance amine light stabilizer did not obviously reduce the lightness of composites, namely fading degree increased, however, it protected the bending quality from losing and reduced the oxidation magnitude of the composites. During UV-weathering, the combination of different kinds of light stabilizer has cooperative effect, which effectively reduced lightness and total color changing, and reduced the loss in the flexural intensity and modulus. Among which the collaborative effect between UV-326(benzotriazoles) and L-944(triazine) was the best.