An Engineering Approach to Plastic Recycling Based on Rheological Characterization

Millions of kilograms of virgin plastics are used annually to manufacture new products, yet only a small percentage of this material is recovered for reuse in new plastic products. Many companies hesitate to use regrind and postconsumer resins (PCRs) because of the extensive testing required to identify plausible uses and processing parameters. Although used polymers may be labeled by general type, such as acrylonitrile butadiene styrene or polycarbonate, such labels do not provide adequate information to determine molding parameters. Because used polymers may be degraded or mislabeled, it is important to characterize the used polymer rather than track the original virgin polymer properties. Another major challenge to plastics recycling is that standard industry polymer databases do not contain information about regrind resins or PCRs. Such polymer databases not only provide selection assistance, but also are used with mold‐filling simulations to reduce the experimental time to determine molding parameters. First, we summarize the current plastics collection, identification, and separation processes. Then, we present an engineering approach for plastics recycling, based on rheological characterization. To characterize the plastic rheology, we measure the viscosity versus shear rate at various temperatures. In our proposed approach, we introduce a sequence of steps to obtain used‐plastic input data for mold‐filling simulations. Our goal is to reduce the amount of experimental testing needed to determine injection‐molding parameters for re‐grind resins or PCRs. We test our method by molding American Society of Testing and Materials test specimens and a thin‐wall application with high‐impact polystyrene from recycled printer and monitor housings. Our tests demonstrate that matching the viscosity versus shear rate curves of PCR and a virgin resin provides a proxy resin for input to mold‐filling simulation software to determine PCR molding parameters. We compare our new approach with other approaches to polymer recycling and discuss directions for future research.