Recyclable sulfur cured natural rubber with controlled disulfide metathesis

Abstract

Traditionally, sulfur-cured natural rubber compounds exhibit limited recyclability due to a significant drop in mechanical performance after reprocessing. Maintaining physical and chemical properties after recycling of a cross-linked polymer is an essential requirement for the global rubber industry to become more sustainable. Here, we demonstrate that tuning the curing process to favour a reversible cross-linked network based on disulfide and polysulfide bonds enables recyclability. We use a sulfur-based vulcanization system optimized with copper (II) methacrylate at concentrations of 2.47, 4.94, and 9.89 phr to control disulfide metathesis at low temperatures and enhance recyclability. Mechanical characterization identifies 2.47 phr as optimal for maintaining mechanical properties after initial moulding and full recovery after recycling. Additionally, we demonstrate that copper (II) methacrylate can be incorporated into existing rubber waste streams to promote recyclability. Cross-linked polymers must maintain physical and chemical properties after recycling to improve sustainability. Here, tuning the curing process to favour a reversible cross-linked network using disulfides and polysulfides bonds retains mechanical performance.