Weathering resistance of pistachio twig-plastic composite treated with nano-copper oxide

Nowadays, demand for the use of wood-plastic composites in outdoors is growing. But, wood deterioration agents such as weathering that lead to the color changes and the surface hydrophilicity increase limit the use of these products in outdoors. Therefore, these products need to be protected in outdoors. Different chemicals have been used to impart weathering resistance to wood-plastic composites. Nano-copper oxide has the potential to be used in the protection of wood plastic composites against weathering because of its thermal stability at the temperatures used for manufacturing wood-plastic composites and because of imparting weathering resistance to wood. Hence, in this research the effect of nano-copper oxide treatment on the weathering resistance of polypropylene-pistachio twig flour composite was investigated.

For this purpose, polypropylene- pistachio twig flour composites treated with nano-copper oxide at four loadings, namely 0, 1, 2 and 3 percent (by weight) were cut to specimens with the dimensions of 50×50×10 mm. The color characteristics and the droplet contact angel of the specimens were measured according to ASTM D 2244 and ASTM D 5446 respectively, before and after exposure to a natural weathering for 180 days in Shast Klateh educational state forest located in the north of Iran: The contact angle up to 10 s after droplet application for the treated and untreated samples was measured using a contact angle analyser PG-X. The color measurements were carried out using color guide 45/0.

The statistical analysis of the color change data showed that nano-copper oxide improved the weathering resistance of polypropylene- pistachio twig flour composite. The color stability of polypropylene- pistachio twig flour composite during weathering was improved with increasing nano-copper oxide loading. The results of the contact angel test also showed that nano-copper oxide treatment resulted in a reduction in the contact angel change due to weathering.

The results of this study showed that treatment with nano-copper oxide resulted in improving the performance of polypropylene-pistachio twig flour composite after exposure to 180 days of natural weathering. With increasing the loading of nano-copper oxide, both the photostability and the hydrophobicity were improved. The improvement in the weathering resistance of polypropylene- pistachio twig flour composites was attributed to the protection of lignin or other compounds of the composite by treatment with nano-copper oxide.