Advances in recycling of waste vulcanized rubber products via different sustainable approaches

Abstract

The recycling of waste vulcanized rubber (WVR) products is highly challenging due to the presence of a three-dimensional (3D) sulfur crosslinked network hindering the natural degradation process. Traditional disposal approaches such as combustion, stockpiling, and landfilling create several environmental concerns by generating toxic fumes and gases causing serious health issues. The best approach to resolve these problems is to reuse/recycle waste materials using sustainable methods for minimizing the negative impact of the current waste handling systems. The recycling of WVR products requires the breaking of the 3D crosslinked sulfur network using environmentally benign devulcanization and/or depolymerization strategies. Pyrolysis is another important process to recycle the WVR products into value-added chemicals. It is important to adopt sustainable approaches to recycle the WVR products into new products. The present review covers various sustainable technologies with the state-of-the-art development of recycling of waste tire and non-tire rubber products. Important processes such as physical, chemical, and biological devulcanization methods involving selective carbon–sulfur (C–S) and sulfur–sulfur (S–S) bond breakage along with depolymerization and pyrolysis are also discussed.