Mitigation of zinc leaching from waste ground tire rubbers through polymer encapsulation

The increasing disposal of waste tires is a growing environmental challenge requiring innovative recycling and reuse approaches. Crumb rubber, derived from end-of-life tires, has potential for various applications where resilience and elasticity are required. However, as highlighted by the upcoming ban on using crumb rubber granulate as infill for artificial turf in the EU, one of the most prominent issues, zinc leaching, urgently requires an effective solution. We studied a range of commercial polymer coatings as a zinc leaching barrier through batch and column leaching tests. This study demonstrates that coatings can reduce the leaching down to 1 % of that of uncoated rubber, reducing environmental risks while improving the prospects for continued use of crumb rubber in various applications. The physico-chemical relation between the coating structure and zinc leaching is elucidated for the most promising coatings by comparing the leaching results with FTIR, GPC and ¹H NMR analyses. The use of certain additives shows a cumulative effect to further reduce zinc leaching, while improving UV- and moisture stability. Thermal stability is controlled by the stability of the polymer base. These findings allow us to tailor the mechanical properties to various applications requiring specific elasticity and durability, while retaining the versatility and adaptability of crumb rubber in a range of scenarios. Additionally, the use of additives, typically cheaper than the polymer matrix, enhances the economic viability. By effectively controlling zinc leaching and tailoring mechanical properties through coatings, this study offers a way to extend the life and utility of waste rubbers.