ABSTRACT

Vulcanized rubber, due to unique characteristics, has seen main uses in automobiles, mostly as tires. Even with the latest shifts in the industry toward electrical drives, vehicles still ride on tires. Today, tires reported in the public domain consist of about 19% natural rubber and 24% synthetic rubbers, while plastics, metal, fillers, and additives make up the rest. Globally, the rubber industry claims to produce over 1.6 billion tires annually, and waste managers report returning a billion waste tires; the rest remains with the users, breaks down in service, or illegally pills in dumpsters. Tires of extensive designs and complex manufacturing withstand the harshness of service life. Consequently, their disposal creates monumental technical and industrial challenges. Current disposal strategies to retiring tires—consisting of incineration, crumb rubber generation, and landfilling—show clear shortcomings. Waste tire rubber recovery and regeneration are preferred for rubber sustainability and rubber product circular economy. Multiple devulcanization processes introduced selective cleavages of the crosslinks of the vulcanizate while retaining polymeric networks. We review devulcanization methods explored, such as chemical, mechanical, biological, and their combinations. We present additional steps necessary to turn postconsumer goods based on rubbers (like end-of-life tires) into engineering materials and products. We offer a new perspective on sustainable waste rubber recovery and reuse. In a follow-up paper, we will discuss the steps to put postindustrial rubbers and rubber products back into production, toward zero waste rubber and rubber product manufacturing.