Endowing rubber with intrinsic self-healing properties using thiourea-based polymer

Abstract

Self-healing polymers are extensively researched for the sustainability of materials. The introduction of dynamic networks instead of traditional cross-linkers for an autonomous healing mechanism in elastomers is a promising strategy for improving rubber properties. However, exchangeable covalent bonds in a dynamic network generally rely on external stimulants and fillers, which can compromise the material's performance. Herein, we introduce a mechanically strong yet resilient and independent self-healing polymeric network by dual cross-linking of bonds based on covalent and non-covalent dual interaction. The thiourea-based polymer polyether thiourea ethylene glycol (PTUEG) was blended with natural rubber (NR) and epoxidized natural rubber (ENR) to strengthen the mechanical characteristics of the material NR-ENR-PTUEG₃. In the material, the thermoplastic polymer PTUEG₃ applied the thiourea linkage as a hydrogen bonding and dynamic covalent motif together to enhance mechanical adaptability in a self-healing polymer network exhibiting stiffness, toughness, and resilience, thereby extending its longevity. The resulting mechanical characteristics of the NR-ENR-PTUEG₃ with 25 phr PTUEG₃ exhibited tensile stress 4.8 ± 0.3 MPa and high elongation at break 833 ± 0.1%, demonstrating far better performance than that of pristine NR, and 85% recovery of its original strength at ambient temperature. The healing behaviour is strongly influenced by thiourea-based polymer contents, enabling autonomous self-healing at ambient temperature, exhibiting in situ load-bearing efficiency in the repaired material, and maintaining their mechanical characteristics.