Temperature modulated DSC for composition analysis of recycled polyolefin blends

Post-consumer plastic waste contains blends of numerous types of polyethylene (PE) and isotactic polypropylene (i-PP), whose recycling is challenging due to the complexity of this waste stream. A comprehensive knowledge of the composition of these recyclates is essential to understand the structure-property relationship of these systems and therefore upcycle them for high-value applications. To this aim, we used Temperature Modulated DSC (TMDSC) to develop a quantitative method to evaluate PE and Low-density PE (LDPE) content in recycled polyolefin blends. TM-DSC was carried out on 29 virgin PE materials, spanning densities between 960 and 862 kg/m3, characterizing a wide range of PE microstructures. Moreover, several PE/i-PP model blends were prepared by selecting LDPE, High-density PE (HDPE) and Linear Low-density PE (LLDPE) materials to blend them with i-PP of three types: homopolymer (PP-H), block copolymer (PP-B) and random copolymer (PP-R), mimicking the composition of real recyclates. Results from the TM-DSC analysis of these blends allowed us to establish methods for quantifying the amount of overall PE content and also the LDPE fraction within recyclates. The developed methods were applied to real post-consumer recycled grades, and results were compared with the ones obtained from Cross-Fractionation Chromatography (CFC) analysis and Nuclear Magnetic Resonance (NMR) spectroscopy, displaying good agreement between the latter and the TM-DSC method.