Plastics recycling, as a subclass of material recovery and recycling, features extensive and intensive properties. The intensive properties can be used to define a recyclability criterion and to classify the plastic materials for a symbiotic system (industrial, municipal and commercial) into recyclability categories, where the materials with higher recyclability can be either recycled/reused within the same category or cascaded and made available to categories with lower recyclability. The potential surplus waste materials of lowest-grade recyclability would be destined for waste treatment and disposal, while the potential deficit of materials in the highest-grade recyclability category would have to be fulfilled by supplying fresh plastic material produced from primary raw materials. The current contribution takes this problem formulation as a basis to optimise the plastics recycling of industrial symbiotic systems. It defines a Plastic Material Cascade Diagram and an associated set of Supply-Demand Composite Curves, identifying the recycling bottleneck – a Pinch Point limiting the rate of recycling and determining the most efficient material recycling network design. A case study is formulated to illustrate the usefulness of the new concept in reducing the consumption of raw materials and final waste.
