Micromechanical modeling of devulcanized ground tyre rubber, graphene platelets, and carbon black in recycled natural rubber blends

Waste tyres are a global problem, with 1.5 billion being generated annually. To reduce this problem, a circular economy for tyres should be developed. This requires the incorporation of recycled tyre rubber in tyre products. Yet, most recycled rubber is of insufficient quality. Recycled rubber must react sufficiently well with virgin rubber to be elastically effective in the 3D crosslinked network. Although a broad range of devulcanization techniques have been developed, many recycled-virgin rubber blends show significant reductions in stiffness compared with their virgin counterparts. This paper demonstrates that micromechanical models for filler reinforcement can be used to evaluate whether recycled rubber behaves in an elastically effective manner. Furthermore, mechanical devulcanization of ground tyre rubber (GTR) by solid-state shear milling was shown to produce a recycled rubber powder that is elastically effective when blended with virgin natural rubber (vNR). These blends match the equivalent virgin rubber stiffness, despite high-recyclate content (30/70 vNR/GTR). The addition of nanofillers (carbon black and graphene nanoplatelets) to these blends was evaluated to see how they compared with virgin compounds and filler reinforcement theories. This process may allow for incorporation of devulcanized rubber into existing products, promoting a circular economy for high-value rubber recycling.