Design And Properties Of High Strength Self-healing Elastomer At Room Temperature

The properties of polymers are inevitably damaged during their molding,processing,and use.Introducing the self-healing ability into synthetic material can realize the repair of internal and surface cracks spontaneously,thus largely eliminating the damage after fracture.Otherwise,the safety,stability and service life of the materials are significantly improved,and finally achieving the sustainable development of resources.The achievement of self-healing relies on the mobility of molecular chains and the dynamic balance of the interactions in the system.However,as more and more self-repairing materials have been reported,it still remains a challenge to balance the polymers'mechanical properties and self-healing ability.The contradiction between mechanical properties and self-healing ability has chronically restricted the application of self healable materials.Aiming at those problems above,a novel polyurethane elastomer with high mechanical robustness and ability to self-healing at room temperature,based on multiple reversible interactions,was designed in this paper.Moreover,the relationship between its structure and properties,and the self-healing mechanism were studied as well.By introducing multi-strength hydrogen bonds,aromatic disulfide bonds and coordination interactions into the elastomer,a self-repairing poly?urethane-amide?elastomer with excellent strength and high repair efficiency was prepared.The results of FT-IR showed that there are strong hydrogen bonds in the system,which are beneficial to the self-repairing of the material.ATR analysis under different strains showed that the coordination bonds can recombine rapidly at room temperature due to its combined strong and weak coordinated structure.X-ray results indicated that the introduction of coordination bonds facilitates the migration of hard segments.DMA results showed that the introduction of disulfide bonds makes the activation energy of the main transition become lower,and the chain mobility is stronger after combining with multiple actions,thus attaining better repairing effect.XRD results showed that the increase in crystal orientation helps to improve the mechanical strength of the material,whereas being harmful to the recovery of elongation at break.AFM results showed that properly increasing the degree of microphase separation can improve the strength and self-repair efficiency simultaneously,but it hinders the recovery of elongation at break.The repair test showed that the original strength of the elastomer is as high as 16.1±0.6 MPa,and the elongation at break can reach 771±36%.After repairing at room temperature for 24 h,the spliced samples can recover 94%of the original strength.To further improving the stability of synthetic elastomer and developing its elasticity,we prepared a room temperature self-repairing elastomer with higher strength,and investigated the influence of coordination density,cross-link density and soft segment structure to the polymer's self-healing property.The results of XPS and stress relaxation tests showed that Cu²⁺in the coordination structure can accelerate the exchange of disulfide bonds and the exchange of oxime-urethane.As a result,under the synergistic effect of the quadruple dynamic bond?disulfide bonds,oxime urethane bonds,coordination bonds and hydrogen bonds?,the original strength of the elastomer is as high as 19.5±1.1 MPa,and the self-healing efficiency at room temperature reaches 83%after healing 48h.Furthermore,it still remains good elastic recovery ability under large deformation.