Catalytic High-Speed Reactive Extrusion for Polyethylene Mechanochemical Upcycling

This study explores a mechanochemical strategy for polyethylene (PE) recycling using ultrahigh-speed twin screw extrusion (TSE), focusing on the synergistic effects of high shear rates and catalyst incorporation to induce structural transformations. By systematically controlling specific mechanical energy (SME), a scalable equipment-independent parameter, the transformation was investigated across two PE structural variations (linear and branched) and linear PE with and without additives. Structural, molecular, and rheological changes were characterized using Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and parallel plate rheology. Catalyst incorporation achieved intimate dispersion and enhanced chain scission, producing low molecular weight liquid and gaseous byproducts collected from the devolatilization zone. Thermogravimetric analysis (TGA) revealed substantial reductions in PE decomposition temperature following catalyst incorporation, attributed to still-active catalyst sites and the formation of labile functional groups such as ethers and esters. These findings establish TSE as a process intensification approach for controlling PE depolymerization with potential as a preconditioning strategy for downstream chemical recycling. By investing mechanical energy upstream to improve polymer catalyst contact and reduce activation barriers, this approach offers a pathway to lower the thermal energy requirements of chemical recycling, contributing to more economically viable and environmentally sustainable polyolefin waste management at industrial scales.