Enabling Polyolefin Circularity through Melt Functionalization and Upcycling

Polyolefins represent the largest contribution to plastic production, use, and generated waste worldwide, yet their recycling rates are low. Current recycling is limited by the inherent cost in and supply chain logistics of collecting, sorting and cleaning diverse plastic composition waste streams, the presence of additives, fillers and inks, and the downgrading of polymer properties during mechanical recycling. The lack of control over polymer architecture and molecular weight invariably results in recycled materials with inferior properties. This presentation will discuss new strategies for recycling and reuse of polyolefin waste through industry-relevant melt-based functionalization processes followed by upcycling to new materials. Specifically, the formation of thermoset polyurethane networks was explored, in which the interplay of crystallization of the polymer and formation of a network architecture governed the resulting material properties. X-ray analysis revealed that the crystal structure of the polyolefin was preserved in the polyurethane network. At room temperature, the polyurethane showed high modulus due to the crystallization behavior of the polyolefin; upon increasing the temperature above the melting temperature, the modulus decreased to a rubbery plateau, consistent with formation of a network. The resulting polyurethane showed higher glass transition temperature and lower degree of crystallinity than its polyolefin predecessor due to the crosslinked nature of the polymer. The mechanical integrity of the polyurethane was maintained through several reprocessing cycles due to the melt processability enabled by the presence of a urethane exchange catalyst. This functionalization and upcycling route thus offers a promising alternative for repurposing polyolefin waste, in which the creation of melt-processable thermoset polymers opens new applications for the materials.