Recycling high impact polystyrene: Material properties and reprocessing in a circular economy business model

An account is presented of successfully implemented Extended Producer Responsibility (EPR) with recycling to high value products, to help overcome barriers and generate confidence in moving towards Circular Economy (CE) business models. A template for organisations proposing to recycle a thermoplastic is provided by describing appropriate tests and considerations in implementing the recovery and re-use of high impact polystyrene (HIPS) based on a practical, industry case. Simulating the repeated 100% closed loop reprocessing of production scrap, original HIPS has been injection molded to produce tensile and impact test pieces, reground and reprocessed eight times. Assessing the present results together with literature, repeated recycling of production scrap is possible without the need for a remedial compounding step, or changes to processing parameters. Integral to the EPR model is recovery of plastic from returned end-of-life (EoL) products, and in relation to the in-use environment, studies of the effects of UV exposure on virgin material show that significant property degradation can occur. However, with indoor use, as in the present case, this is not seen. Within the CE business model it is desirable to use blends of recovered HIPS originating from different original resin manufacturers. Feeding dry blend regrind directly to the molding machine proved satisfactory, avoiding the need for a compounding/pelletizing step. As an outcome of this study, products are being successfully manufactured from 100% HIPS recovered from EoL products in an environmentally and economically positive CE plan.