Influence of Mixing Protocol on Block Copolymer Compatibilized PE/iPP Blends

Compatibilization of poly(ethylene) (PE) and isotactic poly(propylene) (iPP) using block copolymers is a promising approach for recycling mixed polyolefin plastic waste. An EXE triblock copolymer was premixed into commercial PE and iPP followed by addition in a subsequent mixing step of the second homopolymer, where X denotes an iPP melt-miscible poly(ethylene-ran-ethylethylene) random copolymer and E represents hydrogenated 1,4-poly(butadiene). Through transmission electron microscopy, EXE was found to produce micelles in PE and larger aggregates in iPP. The 2-stage blending process led to materials that consistently underperformed in uniaxial tensile testing blend specimens prepared by mixing all three components in a single step. Annealing both PE-rich and iPP-rich 2-stage blended specimens above the melting temperature followed by cooling to room temperature led to recovery of the exceptional toughness (ca. > 400% strain at break) obtained with the single-stage mixing process, but over surprisingly different annealing times. These results reveal distinct process-dependent differences in interfacial localization of EXE in melt blended PE and iPP.