This is an editorial article. It has no abstract.

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.

Dynamic cross-linked networks (DCNs) endow thermoset rubber with self-healability and recyclability to extend its lifetime and alleviate environmental pollution. However, the contradiction between high self-healing and mechanical properties in DCNs rubber is always difficult to be resolved. Herein, we used boronic ester (BO) and Diels-Alder dynamic covalent bonds (DA) to synthesize polybutadiene-based dual networks rubber (PB-BO-DA) via thiol-ene reaction. This approach achieved a tensile strength of 16.46 MPa and 99% self-healing efficiency, facilitated by extensive intermolecular interactions (π-π packing and N-B coordination) and fully dynamic cross-linking. In addition, multiple dynamic cross-linked networks (MDCNs) polybutadiene-based rubber also show excellent shape memory ability and recyclability. This strategy might open a helpful pathway to fabricate intelligent multifunctional polymers with high strength and high self-healing efficiency.

This is an editorial article. It has no abstract.

Thermoplastic vulcanizates (TPVs) were prepared by blending natural rubber (NR) and polypropylene (PP) using dynamic sulfur curing systems with varying accelerator/sulfur ratios: 0.5/2.5, 1.5/1.5, and 2.5/0.5 phr, categorized as conventional (CV), semi-efficient (semi-EV), and efficient (EV). The onset of dynamic vulcanization closely corresponded with scorch time in statically cured NR compounds. Mixing torque decreased over time, reflecting reversion patterns in static curing. The CV system exhibited the highest reversion tendency due to polysulfide linkage breakdown, forming stronger but shorter crosslinks. Dynamic vulcanization induced higher reversion than static curing, influenced by shear and extensional forces. Curing systems caused crosslinking rates, reversion, and crosslink density and distribution variations. Unlike statically cured NR, PP-extracted TPVs exhibited an inverse trend in total crosslink densities and distributions; TPVs primarily comprised shorter crosslinks with opposed total crosslink densities ranked EV > semi-EV > CV. This trend is strongly correlated with superior mechanical strength, toughness, storage modulus, viscosity, and rubber elasticity in the EV-cured TPV. EV system also had the smallest vulcanized NR domains in the PP matrix.