Quantity- and quality-oriented scenario optimizations for the material recycling of plastic packaging in Japan

Abstract

In Japan, the material recycling (MR) of plastic packaging waste faces several problems. Almost half of the collected waste plastics become residue, and the quality of recycled resins is not high because the mixture of various types of plastics makes sorting by resin type difficult. Therefore, an appropriate combination of source separation targets and sorting processes based on plastic type needs to be explored to increase the quantity of waste plastics recycled and enhance the quality of recovered plastics. Furthermore, the acceptability of recovered plastics as raw materials for use in plastic products needs to be assessed by matching the quantity and quality of recovered plastics with the demand and quality requirements of resin users. In this study, we evaluated the purity and quantity of plastics recovered by resin type for 80 combinations of source-separation targets and sorting processes based on the results of a sorting experiment using an actual optical sorter. Then, we developed recycling scenarios that optimized the quantity and/or quality of plastics recovered for MR by allocating waste plastics to the 80 source-separation/sorting schemes using linear programming with the upper limit of the acceptable amounts of recovered plastics and quality constraints. We found that the recycling target established by the Japanese government could be reached, if resin users proactively accepted recycled resin. On the other hand, the current rate of MR could be maintained solely with high-quality recovered plastics, if the collection rate for recycling and the acceptable amounts of the high-quality recovered plastics were significantly boosted.