Mechanical Recycling of Silicone Rubber: Influence of Particle Size and Quantity

Silicone rubber is a widely used elastomer, with a broad range of applications across many industries. Injection moldable liquid silicone rubbers (LSR) are one type of silicone with high production quantities, and hence production waste generated. Nevertheless, there are few efforts to recycle silicones and LSRs in particular. Reported approaches mainly focus on chemical recycling, whereas mechanical recycling, which is well established for thermoplastic materials, is completely neglected in LSR production and only scarcely published, even though mechanical recycling, which, for example, encompasses the shredding and reintroduction of sprues and runners in the injection molding production process, is the higher value reutilization compared to chemical recycling, where the materials need to be further broken down even to a molecular level. In our study, we investigated a mechanical recycling approach of LSRs by introducing ground particles as filler to silicone matrix material. We examined the influence of Shore A hardness, degree of shredding, and amount of filler used. LSRs with Shore A hardnesses of 30, 50, and 70 were used. The particle sizes were varied from 1.0 down to 0.2 mm, and the amount of filler added to LSR was between 10 and 30 wt%. Our results reveal good mechanical properties, differing from the original properties only to a small extent, and no consistent trends regarding the influence of the particle size were found. Even if there are still obstacles to overcome in industrial processes, our study could encourage consideration of mechanical recycling of production scraps also for silicones as a way to contribute to waste reduction.