One-Step Radical-Induced Synthesis of Graft Copolymers for Effective Compatibilization of Polyethylene and Polypropylene

The synthesis of copolymers from high-density polyethylene (HDPE) and isotactic polypropylene (<i>i</i>PP) has gained increasing attention due to their ability to improve the recycling of incompatible mixed polyolefin waste feed streams. Herein, we report a new radical grafting process that yields HDPE-<i>g</i>-<i>i</i>PP copolymers from HDPE and <i>i</i>PP by using a commercially available peroxide. Tensile testing of brittle 70/30 HDPE/<i>i</i>PP mixtures with these graft copolymers added showed promising compatibilization, improving the elongation at break of the blends from 20% up to 1080%. Detailed kinetic studies coupled with thermal and rheological characterization revealed optimized conditions for HDPE and <i>i</i>PP macroradical coupling and a deeper understanding of the grafting reaction. This optimization yielded HDPE-<i>g</i>-<i>i</i>PP copolymers that compatibilize HDPE and <i>i</i>PP blends at loadings as low as 2.5 wt %. The versatility of this macroradical grafting reaction was demonstrated by preparing an effective compatibilizer from untreated postconsumer waste plastics.