Oxidization and Chain‐Branching Reaction for Recycling HDPE and Mixed HDPE/PP with In‐situ Compatibilization by Ozone‐Induced Reactive Extrusion

Abstract

AbstractHigh‐density polyethylene (HDPE) and isotactic polypropylene (iPP) are widely used in industrial and residential applications due to their low cost and chemical stability, thus their recycling process can contribute to a circular economy. However, both polymers are non‐polar materials, and the incompatibility with most other materials leads to substantially inferior properties of blends. In this work, we propose a flexible compatibilization strategy to improve the compatibility of HDPE/iPP blends. Ozone is adopted to induce reactive extrusion for rapid oxidation of HDPE and chain‐branching reactions for both HDPE and HDPE/iPP blends. During extrusion process, ozone oxidizes HDPE effectively in a short time and introduces oxygen‐containing groups such as carbonyl and ester groups, which improves the hydrophilicity. The addition of trimethylolpropane triacrylate (TMPTA) could promote branching reaction and facilitate the formation of HDPE‐g‐iPP copolymers, which improved the compatibility for HDPE/iPP. As a result, the impact strength of ozone‐modified HDPE and HDPE/iPP blends increased by 22 % and 82 %, respectively, and the tensile strength also increased. This strategy would have potential applications in the field of sorting‐free and solvent‐free recycling of waste polyolefin plastics.