Properties of rice straw flour and recycled polypropylene composites exposed to accelerated weathering

This research was carried out to investigating on the effect of virgin and recycled plastics on the mechanical, thermal and color properties of composites from rice straw flour (RF) and polypropylene (PP) before and after weathering.
Rice straw flour (RF) was mixed with both virgin or recycled polypropylene (VPP or RPP) and MAPP at 180 °C and 60 rpm in an internal mixer, and the samples were made by injection molding. The mixing ratio of RF/PP and coupling agent amount for all formulations was fixed at 50 wt% and 2 wt%, respectively. The accelerated weathering process by ultraviolet irradiation and water spray was done on the samples for 2000 hours. Then, the mechanical strength, thermal stability and colorimetric of samples were determined.
Results indicated that the color of composites sharply changed after weathering, further reduced flexural strength and tensile modulus of samples. Differential scanning calorimetriy (DSC) test revealed that the melting temperature, crystallization temperature and crystallinity of weathered samples decreased probably due to the polymer chain scission. The highest lightness and color change in the RF/RPP composites was observed. However, the VPP samples had higher mechanical strength and thermal stability than RPP.
Based on the findings, using a recycled polypropylene for manufacture of composites materials applying in exterior environments is not appropriate.