Quantifying the content of various types of polypropylene in high density polyethylene blends

To enhance the effectiveness of mechanical plastic recycling, it is best to separate different types of plastic during collection and recycling. This ensures the integrity and quality of recycled materials. For instance, the presence of polypropylene (PP) in recycled polyethylene (PE) can result in inconsistent and undesirable material, impacting the quality and performance of the recycled PE. This underscores the need for an analytical technique to accurately detect the presence of PP in recycled PE materials. In this study, we propose a quantitative analysis using a solution-based crystallization elution fractionation (CEF) technique to assess the polypropylene (PP) content in high-density polyethylene (HDPE) blends. The proposed methodology inherently distinguishes between the semi-crystalline PP matrix, including Homo-PP and Random copolymer PP, as well as the non-crystalline copolymer PP, and then quantifies each segment. A series of commercially available Ziegler–Natta catalyzed polymers were used to obtain the calibration curves per different type of PP materials, i.e., Homo-PP and Random copolymer PP. These calibration curves were then utilized to quantify Homo PP and copolymer PP (either semi-crystalline ethylene-propylene or amorphous ethylene-propylene) in different virgin polymer blends. The proposed methodology provides a comprehensive approach to characterizing the polypropylene content within polyethylene systems, especially in the context of qualifying polyolefin recyclate or polymer blends. • Quantitative CEF analysis enhances the detection and characterization of polypropylene in high-density polyethylene blends, ensuring superior quality in recycled materials. • Introduced a solution-based CEF methodology capable of quantifying isotactic Homo-PP, Random-PP, and amorphous PP (xylene soluble fraction) in polyethylene blends within a single experiment. • Developed calibration curves using Ziegler–Natta-catalyzed PP and HDPE binary blend systems, incorporating differential CEF profile and branching (CH 3 /1000 TC) information, and validated these curves with known binary or tertiary PP in HDPE blends. • Provided a more comprehensive and accurate tool for PP composition analysis compared to traditional methods, addressing gaps in quantifying Random-PP and amorphous-PP in polyethylene blends.