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By Meysam Hashemnejad (Lyondellbasell).  

Composition analysis of post-consumer recycled blends of linear low- and low-density polyethylene using a solution-based technique

Abstract

Blends of linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) are commonly used in film applications, including those made with post-consumer recycled (PCR) film resins. The ratio of LLDPE/ LDPE in PCR resins can vary based on the complexity of the waste stream, making it essential to determine their composition before incorporating them into virgin resins through mechanical recycling. In this study, we propose a quantitative analysis using a solution-based crystallization elution fractionation (CEF) technique to determine the composition of PCR LLDPE/LDPE blends. The results were compared with those obtained by a standard differential scanning calorimetry (DSC) technique. A series of Ziegler–Natta catalyzed LLDPE resins were blended with LDPE to establish the CEF calibration curves. The CEF calibration curves were found to be similar for 1-butene LLDPE/LDPE and 1-hexene LLDPE/LDPE blends. Fourier transform infrared spectroscopy and nuclear magnetic resonance were used as needed to determine the type of comonomer in the LLDPE component for the DSC methodology, which varies the calibration curve. We found that the CEF and DSC techniques provide comparable results in terms of LDPE content for neat polymer blends, depending on the density of each component. However, the proposed CEF technique provides more accurate and reliable results than previously published techniques in estimating LDPE content in PCR LLDPE/ LDPE blends that may contain inorganic compounds.)

CEF, circular economy, composition analysis, DSC, LDPE and LLDPE blends, plastic recycling, polyolefins, post-consumer recycled resins