Polymer Blend Spiking Method for Quantifying Polypropylene Variants in 100% Polypropylene Blends

Understanding the type of polypropylene (PP) in post-consumer recycled (PCR) PP is valuable for optimizing mechanical recycling approaches, especially when blending with virgin polymers for specific applications. However, accurately identifying and quantifying the various types of polypropylene, including isotactic Homo-PP (Homo-PP), Random-PP, and non-crystalline PP components (such as xylene-soluble atactic PP and amorphous ethylene-propylene copolymers), presents significant challenges when dealing with materials composed entirely of polypropylene. To address this, we propose a solution-based crystallization elution fractionation (CEF) technique to determine the composition of different PP variants in PP blend systems. Our approach involves introducing a controlled amount of linear low-density polyethylene (LLDPE) into the 100% PP sample in solution, enabling the separation of Homo-PP from Random-PP. By applying established calibration curves, we quantitatively resolve the content of Homo-PP, Random-PP, and non-crystalline PP. The calibration is effective across the full composition window, enabling accurate quantification of Random-PP and Homo-PP from pure (100%) components to mixed systems spanning ~5 wt.% to 95 wt.% Random-PP. This comprehensive analysis offers valuable insights into the distribution of PP variants within the material, facilitating informed decision-making in recycling and material selection processes, ultimately enhancing the efficiency and sustainability of PP recycling operations.