Continuous photoelectric recognition for isolation and recycling of colored HDPE plastics derived from post-consumer containers.

The recycling and utilization of waste high-density polyethylene (HDPE) containers is an important component in achieving low-carbon and sustainable development. The automated classification and separation of HDPE materials with different colors serve as a key prerequisite for improving the quality of recycled HDPE and expanding its high-value applications. In this study, a multi-stage photoelectric sorting and recycling process for different colored HDPE flakes is established. This work adopts the Hue-Saturation-Value (HSV) color space conversion strategy. The decoupled characteristics of HSV three-dimensional color channels are beneficial for eliminating recognition interference caused by complex ambient light fluctuations. Post-sorting performance verification demonstrates that differently colored recycled HDPE possess excellent and stable physical and mechanical comprehensive performance. Although minor differences exist in density, ash content, melt flow index and mechanical strength among different colored HDPE, the overall material performances are comparable to commercial virgin HDPE 5502 materials. In addition, the residual heavy metal contents of sorted recycled HDPE are far below the Restriction of Hazardous Substances 2.0 safety thresholds, satisfying commercial reuse and industrial application standards. This developed multi-stage photoelectric color sorting technology significantly improves the recycling efficiency and product added value of waste multi-color HDPE. This work provides a feasible technical solution for the intelligent and high-value recycling of waste HDPE plastics. And this work offers a valuable reference for precise sorting and resource regeneration of post-consumer plastic wastes.