Rubber Recycling: Mending the Interface between Ground Rubber Particles and Virgin Rubber

The interface between ground rubber particles (GRPs) and virgin rubber is the focus of this investigation that aims to mitigate the detriments caused by recycled GRPs blended in virgin rubber. By studying laminates of cured and uncured rubber strips as models for the interface, modulus contrast across the interface has been identified as another cause for the poor mechanical properties of vulcanizates containing GRPs, in additional to poor interfacial bonding. A surface-devulcanization method was established to improve molecular contact between the GRPs and virgin rubber and consequently raised the adhesion energy to the level of cohesion energy. The interfacial modulus contrast that causes stress concentration at the interface was likely a result of diffusion of curatives from the virgin rubber to the GRPs. The modulus contrast was erased by diffusion of piperidine from the GRPs into the virgin rubber. Piperidine acted as a vulcanization accelerator, making sulfur cross-linking within the virgin rubber outcompete sulfur diffusion into the GRPs. Mending the interface improved the tensile strength of vulcanizates containing GRPs to a level close to that of the virgin rubber vulcanizate but did not improve the extensibility.