Structures of the co‐branching reactive products of isotactic polypropylene with high‐density polyethylene and the effect on the in situ compatibilization of mixed recycled materials

Abstract

AbstractThe recycling of petroleum‐based polymers such as polypropylene (PP) and polyethylene (PE) is an effective means of reducing environmental pollution. However, the incompatible PP and PE blended waste is difficult to separate accurately, which reduces the quality of the recycled material. In this paper, the trifunctional acrylate monomer (trimethylolpropane triacrylate), peroxide (2,5‐dimethyl‐92,5‐di[tert‐butylperoxy] hexane) and free radical activity modifier (zinc dimethyldithiocarbamate) were applied to in situ generate the copolymer of isotactic polypropylene and high‐density polyethylene (iPP‐co‐HDPE) with a long‐chain co‐branched structure via a melt blending method. The co‐crystallization of the branched copolymer chain segments with the chemical identical homopolymers vastly improved the compatibility of iPP and HDPE components. This in situ co‐branching compatibility strategy resulted in a significant improvement in the mechanical properties of PE and PP mixed wastes. The temperature gradient extraction method was used to separate the co‐branching modified iPP/HDPE blends. The results confirm that the separated iPP‐co‐HDPE components have a highly co‐branched structure. The significant improvement in compatibility resulted in a large increase in elongation at break and impact strength of the iPP/HDPE blends, which provides an economic and effective method for the recycling of mixed PE and PP wastes.