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

Abstract

High-density polyethylene(HDPE)and isotactic polypropylene(iPP)are widely used in industrial and residential applications due to theirlow cost and chemical stability, thustheirrecycling process can contributeto a circular economy. However, both polymers are non-polar materials, and the incompatibility with most other materials leadsto substantially inferior properties of blends. In this work, we propose a flexible compatibilization strategy to improve the compatibility of HDPE/iPP blends. Ozone was adopted to induce reactive extrusion for rapid oxidation of HDPE and chain-branching reactions for bothHDPE and HDPE/iPP blends. During extrusion process, ozone oxidizesHDPE effectively in a short time and introducesoxygen-containing groupssuchas carbonyl and ester group, which improvesthe 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.