Influence of a Stabilized Cap Layer on the Photodegradation of Coextruded High Density Polyethylene/Wood-Flour Composites

摘要

The effect of light stabilizer's addition method into wood-plastic composites (WPCs), i.e., surface versus bulk, on their photostability was evaluated. Blends of ultraviolet absorbers (benzotriazole or hydroxyphenyl-triazine) with a hindered amine light stabilizer were used as the stabilizing additives. Both unstabilized and photostabilized uncapped (control) samples, as well as coextruded WPCs counterparts, were exposed to up to 3000 h of accelerated artificial weathering. The light transmittance, surface morphology, and color of the samples before and after weathering were analyzed by UV-vis spectroscopy, SEM, and Chroma Meter. The experimental results indicated that the method of adding the light stabilizer had a significant effect on the WPC photostability. While bulk addition reduced the degree of fading in uncapped composite, it did not suppress it completely. On the other hand, coextruded WPCs with photostabilized cap layers showed no visible signs of fading, thus clearly indicating that the stabilized cap layers blocked most of the UV radiation, and thereby prevent of UV light to reach the surface of the inner layer of coextruded composites. Cost-analysis considerations indicated that 50 times more light stabilizer was needed when it was incorporated into the bulk of the composites rather than in the cap layer of coextruded samples. Clearly, these results suggest that adding light stabilizers at the surface of WPCs not only protects them against UV degradation, but also is a most efficient and cost-effective method of photostabilization than bulk addition.