Study on a Method of Contamination Removal for Recycled PP Sorted from Discarded Household Appliances and the Identification of Materials that Accelerated Thermal Oxidation Degradation

Material recycling is a meaningful way to reduce environmental impacts and costs simultaneously. Mitsubishi Electric Corporation has realized “closed-loop recycling from household appliances to household appliances” in which polypropylene (PP), polystyrene (PS) and acrylonitrile-butadiene-styrene (ABS) are collected from a mixture of residual plastics contained in discarded household appliances and sorted for recycling. In this research, the dark-colored recycled PP and the light-colored recycled PP were separated from the mixed-colored recycled PP using a color sorter, and the recycled PP was polished using a plastic polisher to remove surface contamination. As the number of surface polishings of the recycled PP increased, the heat life became longer, so a clear correlation was seen between the heat life and the amount of contamination. From the relationship between the amount of residual copper in the recycled PP and the heat life, it is necessary to set the amount of residual copper in light-colored recycled PP to less than 3 ppm in order to obtain a heat resistance comparable to that of virgin PP without adding a metal deactivator.