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

Abstract

The degradation of waste vulcanized rubber (WVR) products is highly challenging due to the presence of a three-dimensional (3D) sulfur crosslinked network that hinders the natural degradation process and keeps it intact in the environment for long durations. Traditional disposal approaches such as combustion, stockpiling, and landfilling create several environmental concerns by generating toxic fumes and gases causing serious health worries. To resolve these critical problems the best way is to reuse/recycle these waste materials using sustainable approaches that reduce the negative impact of the current waste handling system on health and the environment. The recycling of WVR products mainly requires the breaking of the 3D crosslinked sulfur network using environmentally benign devulcanization and/or depolymerization strategies. In addition, pyrolysis is another critical process to recycle the WVR products into value-added products. It is crucial to adopt sustainable approaches to recycle the WVR products so that the recycled rubber can be used in new products to replace the virgin rubber. In this review, various sustainable technologies with state-of-the-art development of recycling of WVR products such as waste tire and non-tire rubber products are summarized. Detailed discussion about the important techniques such as physical, chemical, and biological devulcanization methods involving selective C-S and S-S bonds breakage along with the depolymerization and pyrolysis process is included.