Crystallization of recycled polyolefin blends: molecular characterization and surface nucleation

This PhD thesis addresses the critical need for accurate characterization of post-consumer recycled (PCR) polyethylene (PE) and polypropylene (PP) blends, essential for their repurposing in high-demand applications. The study significantly improves the accuracy of the temperature rising elution fractionation coupled with gel permeation chromatography (TREFxGPC) method. It employs model blends and virgin polymers to estimate polymer-specific IR-detector response factors and introduces a correction for PP's molecular weight-dependent elution in the PE characteristic TREF temperature range. This refinement reduces the error in composition determination from 8% to 2%, enhancing the quantitative assessment capabilities for recycled blends. Furthermore, the crystallization dynamics in PP/PE blends is explored, revealing an increase in PE crystallization temperature when the PP matrix underwent a self-nucleation protocol, due to an epitaxial nucleation mechanism. Notably, this increase depends on the PE chain regularity. Finally, the research also demonstrates the efficiency of a fast scanning SSA protocol, applied on differential scanning calorimetry, reducing the analysis time of polyolefin blends significantly, still providing high resolution results. These advancements in characterization techniques not only provide a deeper understanding of blend microstructures but also pave the way for using PCR materials in more demanding applications, contributing significantly to the field of polymer recycling.