(164aa) Development of a Rubber Recycling Process Based on a Single Component Interfacial Adhesive

By 2040, the number of cars in service is expected to reach 2 billion globally, highlighting need for sustainable methods to reclaim and recycle the millions of tons of waste tires generated each year. Currently, no adequate technology exists to repurpose waste rubber on a large scale; in 2017, less than 25% of natural rubber (NR) from scrap tires was reused in ground rubber applications. Rubber recycling is challenging because vulcanized rubbers are difficult and costly to process, and common devulcanization and recurring processes produce recycled materials with substantial degradation in properties. One alternative to devulcanization is to improve incorporation of the ground rubber particles (GRP) into the polymer matrix by GRP surface modification, thereby minimizing defects that spur delamination.

Here, a simple and cost-effective adhesive-based rubber recycling process was designed as an alternative to devulcanization. Interfacial bonding between vulcanized and virgin rubber was improved by incorporating novel adhesives and coating processes during rubber re-blending, reducing interfacial defects that cause premature failure. In flat laminates, bond strength between vulcanized and virgin material doubled when a vulcanizing fluid and thin adhesive layer were introduced. These components were combined into single-component adhesives (SCAs), which improved bond strength six-fold over no treatment, using half the raw material as the multi-layer adhesive. When SCAs were coated onto vulcanized rubber particles prior to re-blending, the best rubbers exhibited nearly 50% increases in mechanical strength and toughness versus the untreated control, with no loss in extensibility; all treatments improved mechanical strength. This simple, inexpensive, and scalable process can be implemented with one step beyond standard re-blending and curing, providing a promising alternative to devulcanization for polymer recycling.