A novel approach for accurate determination of polyethylene and polypropylene content in polyolefin blends and recyclates by cross-fractionation chromatography

The accurate characterization of post-consumer recycled (PCR) polyethylene (PE) and polypropylene (PP) blends is essential for repurposing them into higher-demand applications. This study improves the accuracy of the Temperature Rising Elution Fractionation coupled with Gel Permeation Chromatography (TREFxGPC) approach for both virgin and post-consumer recycled PP/PE blends. Model blends and virgin polymers were used to estimate polymer-specific IR-detector response factors. Moreover, a correction for the molecular weight-dependent amount of PP eluting in the TREF temperature range characteristic of PE was found. Accounting for these factors improved the results of the method, reducing the error in composition determination from 8 % to 2 %. Therefore,our approach provides better quantitative assessment capabilities for recycled blends. Furthermore, the refined TREFxGPC not only reliably determines the PCR PP/PE blend composition but also reveals their bivariate molecular weight and chemical composition distribution (MWD-CCD). Understanding the full microstructure of the blend can lead to superior recycled products, enabling the use of PCR in more demanding applications.