As a complex composite material, tire rubber has always presented significant environmental and waste management concerns due to its non-biodegradability and accumulation in landfills. The devulcanization of tire rubber has emerged as a historical challenge in the field of sustainable rubber engineering since Goodyear invented cross-linking in 1839. This review provides a comprehensive analysis of waste tire recycling processes, focusing on the sources, legislation, management strategies, and utilization across different regions. It explores the multifaceted challenges of devulcanizing rubber, with a specific focus on transitioning from ground tire rubber to the concept of multi-decrosslinking: sulfur bridge breakage, rubber chain depolymerization and micro-nano sized core-shell carbon black. Ideal devulcanization has restricted the release of reinforcing fillers, resulting in devulcanized rubber mainly containing dozens of micron particles, which hinder the wide usage of devulcanized rubber. This review comprehensively assesses the current state-of-the-art techniques for tire rubber devulcanization, including physical, chemical and biological methods. It explores the intricacies of ground tire rubber as a starting material, structural evolution of ground tire rubber during the devulcanization process and the associated challenges in achieving efficient devulcanization while retaining desirable mechanical properties. Furthermore, through an in-depth analysis of recent advancements, limitations and prospects, this paper offers a complete understanding of the challenges faced in tire rubber devulcanization. Considering the technical and environmental aspects of these processes, this work contributes to multi-decrosslinking, the ongoing discourse on sustainable materials development and circular economy initiatives, which pave the way for future innovations in the field of rubber recycling.

Our work reveals a notable shift in the crystallization temperature (T_c) of poly(butylene terephthalate) (PBT) at which crystallization occurs due to exposure to prolonged thermal degradation at 270°C in an environment of nitrogen gas. The initial T_c of 193°C undergoes a marked decrease, settling at 133°C, which signifies a considerable 60°C shift towards lower temperature ranges. This transition is discernible across three distinct degradation stages: an initial phase of increase, an intermediate phase characterized by a sharp decline, and a subsequent late stage of the degradation phase characterized by a more moderate decrease in T_c. Both crystallinity and crystallization kinetics consistently mirror this pattern, demonstrating an initial rise, a rapid subsequent drop, and a gradual decline in the late-stage period. Evident from the presence of two melting peaks, the research implies differing lamellar thicknesses. As the degradation progresses, the melting points of these peaks, denoted as T_m1 and T_m2, decline at 38 and 41°C, respectively. Validation of the degradation-induced changes is provided by a small angle X-ray scattering (SAXS), which corroborates the observed decrease in the long period (L). A contextualization of the results against prior studies underscores analogous trends in the alteration of crystallization behaviour consequent to degradation.