Aging Resistance Of Rice Hull Powder/Recycled HDPE Composites

In this paper, the performance of rice hull (RH) powder/recycled high density polyethylene (HDPE) composites experienced accelerated aging (thermo-oxidative aging, ultraviolet aging) was studied. Effects of environmental factors and anti-aging agents (HALS, UV absorbers, and pigment) were discussed based on the data from mechanical property test, color analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray energy analysis. The results showed that:1.FTIR analysis revealed that the recycled HDPE used in this research contains a little amount of PVC and PP. Carboxyl groups appeared in HDPE samples, which indicated that recycled HDPE was oxidized during manufacturing or using. Compared to the RH/virgin HDPE composite, the color difference of the RH/recycled HDPE composite reached up to 20 units. Despite the component of recycled HDPE was not pure and the oxidation occurred, RH/recycled HDPE composite provided good bending strength.2.RH/recycled HDPE composites changed into darker color after thermo-oxidative aging; its flexural strength increased at a rate of 4MPa/32h in the initial stage, but improved magnitude decreased after 128h. Crystal structure of HDPE transitioned with the thermo-oxidative aging conducted.,the size of crystal grew and crystallization increased in the early aging duration before 64h, then the crystallization reached saturation The analysis of FTIR indicated that carbonyl index and wood index of RH/recycled HDPE decreased after thermo-oxidative aging;,By SEM observation it was found that the surface of RH/recycled HDPE composite became rough and spots appeared on it after thermal oxidative aging. Both FTIR and SEM showed that the rice hull powder degraded during thermo-oxidative aging. The increase in mechanical properties was due to the improved compatibility between rice hull powder and HDPE matrix and stress of some chains released in the thermo-oxidative aging. Iron red played a role in stabilizing colour.3.As rice hull powder/recycled HDPE composites was exposed to accelerate ultraviolet aging, chain scission, crystal and cross-linking occurred simultaneously. In the first 1000h aging, chain scission was dominant and the crystal structure of HDPE changed to some extent. After 1000 h of exposure, chain scission and cross-linking tended to be balance and the mechanical strength also tended to be balance, accordingly. During 1500h-2000h, cross-linking increased in this stage and the mechanical strength improved4.UV absorbers (UV326) and photo-stabilizers (HALS770) have a good synergism effect. The loss of UV326 during UV aging was mainly due to the washing out in the process of condensation cycle. When UV326, HALS770 and iron red were used simultaneously, color, mechanical strength and surface morphology of RH/recycled HDPE composite presented best results.