Compatibilization of Polyolefin Blends Under Shear

Recycling of post-consumer polyolefins such as polyethylene (PE) and polypropylene (PP) is hindered by sortation difficulties and so recyclates typically come in mixed form. Unfortunately, blends of PE and PP are immiscible and form brittle materials with micro-separated domains when melted together. To overcome this challenge, additives, such as block polymer compatibilizers, have been used to strengthen the material, however, the effect of the compatibilizer on the crystallization behavior of each component is not well understood. In this work, we study a PE/PP blend compatibilized with a poly(ethylene-cb-propylene) comb block copolymer and examine the effect of the compatibilizer on the crystallization kinetics both with and without shear. Using a combination of rheo-Raman spectroscopy, scanning electron microscopy, and differential scanning calorimetry, we explore the effects of shear temperature and overall strain on the rheological properties, crystallization behavior, and morphology of the compatibilized blend. Results show that the compatibilizer enhances crystallization in PE and PP alone but suppresses crystallization in the blend due to the decrease in domain size. Additionally, under shear, stronger flow-induced crystallization is observed in the blend both with and without compatibilizer when compared to the homopolymers, attributed to the morphology and micro-flow fields.