Effects of UV Aging, Water Storage and Recycling on Mechanical Properties of Biogenic Wood-Plastic Composites from Polyamide 11

Abstract

In this study, the weather stability of a biogenic wood-plastic composite (bio-WPC) made of bio-based polyamide 11 (PA11) and 30 wt% of beech wood particles (BP) by twin-screw compounding is evaluated. It is found that UV aging has no significant effects on the modulus of elasticity and tensile strength of the injection molded bio-WPC due to the UV stabilization of the PA11. It is also found that the water absorbed by the hydrophilic beech wood particles and by the PA11 matrix during water storage acts as a plasticizer and results in a decrease in stiffness and strength as well as an increase in the elongation at break. The second focus of this study is the evaluation of the mechanical properties after recycling. It is found that recycling leads to a reduction of the modulus of elasticity and tensile strength by 18% respectively 19%, compared to the original bio-WPC. These effects are attributed to a mechanical and thermo-oxidative degradation of the beech wood particles but also of the PA11 through recycling by granulation and repeated injection molding. A corresponding drop in stiffness and strength is typical for recycled composite materials. Overall, the recycled bio-WPC therefore has a good level of mechanical properties after recycling.