Degradation indicators in multiple recycling processing loops of impact polypropylene and high density polyethylene

Abstract

In a circular economy, polymeric materials are used in consecutive loops to convert by-products of one application to a valuable product for another. This reprocessing, however, entails degradation processes in the polymers, which manifest as changes in the material properties. This study looks at the impact of several closed recycling loops on the material properties of two different polyolefins: Polypropylene impact copolymer (PPc) and High Density Polyethylene (HDPE). Relationships between polymer chemical features and processing behavior were sought. The samples were characterized using melt flow index (MFI), in-line capillary rheometry, infrared spectroscopy, differential thermal analysis (DSC), thermogravimetric analysis (TGA) and mechanical tensile testing. The polyolefins processability and process stability, on the other hand, was assessed in through injection molding parameters monitoring. Though evidences of chain scission for PPc and chain branching for HDPE were found, the examined polyolefins revealed low damage to mechanical properties and the possibility for future industrial reemployment at least up to 3 consecutive processing loops for both polymers.