# Structural, Thermal and Mechanical Assessment of Green Compounds with Natural Rubber
###### Abstract  
The inadequate disposal of tires poses a significant threat to human health and requires effective recycling solutions. The crosslinked structure of rubber, formed through sulfur bridges during vulcanization, presents a major challenge for recycling because it prevents the rubber scraps from being reshaped thermoplastically. Reclaiming or devulcanization aims to reverse this crosslinking, allowing waste rubber to be transformed into products that can be reprocessed and revulcanized, thereby saving costs and preserving resources. Microwave technology shows promise for devulcanization due to its ability to break sulfur crosslinks. In this study, we investigate the devulcanization of ground tire rubber (GTR) through a combined process applied to samples from both car and truck tires subjected to varying periods of microwave irradiation (0, 3, 5 and 10 min). The devulcanized GTR was then blended with natural rubber (NR) and underwent a new vulcanization process, simulating recycling for novel applications. The GTR was mixed with NR in proportions of 0, 10, 30 and 50 parts per hundred rubber (phr). This study also examines the differences between the GTR from car tires and GTR from truck tires. The results showed that the treatment effectively breaks the crosslinks in the GTR, creating double bonds (C=C) and improving the mechanical properties of the revulcanized samples. The crosslinking density and related properties of the samples increased with treatment time, reaching a maximum at 5 min of microwave treatment, followed by a decrease at 10 min. Additionally, the incorporation of GTR enhanced the thermal stability of the resulting materials. F 2024 20  
While research in the field of genetics, cell biology and other bio areas are making discoveries that increase the quality of life and longevity, the reuse and recovery of hazardous materials such as tires is also an effective way to prevent and avoid situations that undoubtedly have a negative impact on human health. Fortunately, as mentioned earlier, the scientific community is continuously exploring new recycling methods to offer more efficient solutions for managing waste. Elastomers are characterized by their crosslinked structure, which is established during the vulcanization process. This process involves the formation of disulfur bridges (-S-S) that link the macromolecular chains of the polymer. The majority of elastomer properties stem from this crosslinked structure. However, these crosslinks also pose a challenge for recycling, as they prevent the polymer from melting and being reshaped thermoplastically. Reclaiming is a process aimed at breaking the crosslinked structure of the elastomers, which transforms scrap and waste rubber in products that can be processed and vulcanized again, simultaneously saving costs in raw materials and preserving both natural resources and the environment. In this way reclaimed elastomers can be incorporated in blends with fresh rubber, forming compounds able to be used in diverse applications [3]. The incorporation and dispersion of the reclaimed rubber play important roles concerning product quality, the production economy and market competition. Reclaiming is also called devulcanization, and the term refers to the process of reversing the creation of disulfur and/or polysulfur bridges in elastomers. Specifically, devulcanization targets the breaking of these bridges, whereas reclaiming generally involves breaking down the chains that form the elastomeric network in a less specific manner. To achieve the process of devulcanization, the breaking of the intermolecular chains that crosslink the elastomers, several methods based on supercritical CO\({}_{2}\)[4], ultrasounds [5], mechanochemical [6; 7; 8] or microbial methods [9], have been proposed. Some of these techniques require reactions that involve organic compounds, oils and solvents and may imply risks for health and the environment.