Plastics Waste Processing: Comminution Size Distribution and Prediction

Complex industrial and consumer products, such as automobiles, contain significant amounts of potentially recyclable materials, but these materials are not necessarily recovered after their useful life. The current recovery process for automotive hulks manages to capture nearly all of the metal content, but few of the plastics. Except for selected high value plastic parts, most remain with the vehicle and are shredded. Extensive hand dismantling, which is effective, is currently not cost-efficient. However, if materials or components can be designed to separate by their characteristic sizes after comminution, then the material recovery from product waste can be enhanced. Such efforts would support industry design-for-environment and design-for-recycling initiatives. In this study, samples made from acrylonitrile butadiene styrene and polyvinyl chloride were assembled with a variety of thicknesses, configurations, and fastening methods, and were comminuted in two passes through a plastics granulator to determine if they resulted in size-based separation characteristics that could be exploited in the recovery process. A detailed evaluation found that particle size distributions fit a modified Gaudin size distribution relationship well. Of all the sample variations studied, only the granulator exit screen size had a significant impact on the average and distribution of comminuted particle sizes. The pi breakage theory, generally advocated for its use in waste processing, did not hold well in this situation of more complex material configurations. The selection function values were found to decrease with the decreasing size of feed particles.