Advancing polypropylene quantification in recycled HDPE: A comparative study of FTIR, DSC, TREF, and TGIC for enhanced plastic circularity

The exponential growth in the production and demand for plastic materials has given rise to significant environmental concerns, highlighting the need for effective recycling strategies to reduce plastic waste and give these materials a new life. Nevertheless, recycling plastic materials present a significant challenge. For instance, even trace amounts of polypropylene (PP) in recycled high-density polyethylene (HDPE) can significantly affect its physical, chemical, and mechanical properties. It is therefore imperative to precisely determine the levels of PP contamination, which is the principal objective of this study, to ensure the quality of recycled materials and compliance with regulatory standards in a range of countries. An alternative analytical technique based on a chromatographic method involving the adsorption of the polymer chains in a support, namely Temperature Gradient Interaction Chromatography (TGIC) is evaluated. To ascertain the efficacy of the proposed method, it has been benchmarked against other established techniques within the recycling industry, such as Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) as well as recently published alternative method, Temperature Rising Elution Fractionation (TREF). This study offers an examination of the advantages and challenges associated with each of these techniques, with the objective of facilitating the selection of an optimal PP quantification method in recycled PE that can enhance the sustainability and quality control of recycled materials. • Reliable PP determination in recycled HDPE for circular economy goals • FTIR usually overestimates PP content due to baseline noise and absorbance issues • DSC requires enthalpy correction to avoid underestimating PP in blends • TGIC accurately quantifies PP in recycled HDPE, outperforming FTIR and DSC