Optimal recycling of waste materials in a plastic extrusion production process

In a plastic extrusion production process, waste materials are created, reground and mixed with virgin plastic raw materials for use in the subsequent production cycles. The recycling of these waste materials helps to reduce the cost of using the more expensive virgin raw materials. However, the yield of the overall extrusion process decreases as a result. In this paper we develop a model to determine the optimal number of regrinding cycles for reusing these waste materials. The objective is to maximize the average profit per production batch. Analytical results are derived to compute the optimal number of cycles efficiently. Two characterizations of the melting index deterioration, which affects the yield of the extrusion process, are studied in detail. Numerical examples are provided to illustrate the results and to analyze the impact of various parameters on the optimal solutions.