Mechanochemical strategies for the catalytic upcycling of polyethylene via transfer hydrogenation

The development of innovative catalytic strategies is crucial to advance the sustainable upcycling of plastic waste. In this work, we present a mechanocatalytic approach for the selective depolymerization of low-density polyethylene (LDPE) into liquid hydrocarbons using 2-propanol as both direct hydrogen donor and liquid-assisted grinding (LAG) agent and potential radical-quenching medium. High-energy milling was carried out in the presence of a commercial Ru/Al2O3 catalyst across four distinct mechanochemical platforms: mixer mill, planetary mill, resonant acoustic mixer and a vibratory disc mill. The influence of mechanical energy input on polymer conversion and product distribution was systematically investigated. Remarkably, under optimized conditions over 95% of the GC-detectable volatile products fall within the C5–C20 range, suitable for fuels and chemical feedstocks. Quantitative GC analysis revealed that 0.47 mg of C5–C20 products (0.188 wt% of the initial polymer) belong to the GC-detectable volatile fraction under optimized conditions. These findings highlight the potential of mechanocatalysis to drive selective valorization of polyolefin wastes under mild, H2-free conditions by coupling mechanical activation with in situ hydrogen transfer.