Study On Gamma Irradiation Damage Behaviors And Irradiation Resistance Of Polyurethane Elastomers

Polyurethane elastomers have both the high elasticity of rubber and the high strength of plastic,and the product performance can be adjusted in a wide range.Those charecters make it become a promising material in nuclear power plants,aerospace and nuclear power system.Under high-energy irradiation environments,such as y-ray,electron beam,the molecular chains and network structures are cross-linked,broken and rearranged,which further causes significant changes in the macroscopic mechanical properties.Therefore,it is significant to comprehensively understand the irradiation damage behaviors of polyurethane elastomers under high-energy irradiation environment,and develop polyurethane elastomers with irradiation resistance characteristics.The mechanical properties of polyurethane elastomers are closely related to their microphase separation structures.At present,the research on the irradiation damage behaviors of polyurethane elastomers mainly focuses on the radiolysis products,aging mechanism and mechanical properties.However,little attention has been paid to the influence of irradiation on the microphase separation structures.Meanwhile,it is still a challenge to improve the irradiation resistance of polyurethane elastomers,and the analysis of irradiation resistance mechanism should be further strengthened.In this paper,the evolution of molecular dynamics,microphase separation structures of polyurethane elastomers under high-energy irradiation environments were systematically analyzed.At the same time,the irradiation resistant polyurethane elastomers were designed by introducing free radical scavengers such as polydopamine and grapheme,and the mechanism of irradiation resistance was revealed.The main conclusions of this paper were as follows:(1)The evolution of dynamics molecular mobility,microphase separation structures of polyether and polyester polyurethane elastomers under gamma rays were analyzed in detail,and the reasons of mechanical properties deterioration were not only related to the irradiation damage of the soft phase,but also caused by the destruction of the hard microdomains.The coordinated motion of soft segments of polyether polyurethane elastomer was enhanced as a result of chain scission.On the contrary,the coordinated motion of soft segments of polyester polyurethane elastomer decreased due to the occurrence of chain crosslink.At the same time,both polyether and polyester of polyurethane elastomers had obvious irradiation scission destruction in the hard microdomains.The evolution of hard microdomains during the stress process was observed by in situ tensile/small angle scattering technique,which explained the decrease of the mechanical properties.In addition,the polyether polyurethane elastomer has a significant irradiation dose rate effect.At low dose rate,the soft segments and hard microdomains of polyether polyurethane elastomers were mainly chain scission.Under high dose rate,the soft segments changed from chain scission to chain crosslink.(2)Polydopamine/polyurethane(PDA/PU)nanocomposites were obtained by physical blending method,PDA nanospheres could rapidly scavenge free radicals,reduced the number of free radicals in PU matrix,and improved the irradiation resistance of PDA/PU composite material.The results of tensile properties show that PDA nanosphere can effectively improve the irradiation resistance of PDA/PU elastomers under gamma rays,especially when the irradiation dose was below 100kGy.The thermal stability of hard microdomains of PDA/PU was hardly affected by the gamma rays.(3)Polydopamine functionalized graphene nanoplatelet(PDA-GNP)with controllable PDA grafted amount was prepared,and then GNP/PU and PDA-GNP/PU nanocomposites were prepared by physical blending method.The results shown that PDA coat improved the interface compatibility between GNP and PU matrix,rapidly quenched the radiation free radicals,and thus improved the radiation resistance of PU.The influence of PDA interface structure on the high-energy irradiation damage behavior of polyurethane elastomers was studied.The tensile properties of PU,GNP/PU and PDA-GNP/PU composites decreased with irradiation dose.The addition of GNP had little effect on the improvement of the irradiation resistance,but PDA-GNP could improve the irradiation resistance at a low amount(less than 0.25 wt%).The reason was that PDA-GNP had a better free radical quenching efficiency,thus improving the stability of the hard microdomains of PDA-GNP/PU composites under high-energy irradiation environments,and then reinforcing the irradiation resistance.Furthermore,GNP and PDA-GNP were incorporated in PU by in situ polymerization.Because the high concentrations of catechol and amine functional groups of PDA can react with isocyanates to form covalent bonds,the PDA-GNP/PU nanocomposites presented high-strength and high-toughness elastomeric without sacrificing extensibility compared with GNP/PU nanocomposites.With only 0.5 wt%PDA-GNP,the tensile strength of PDA-GNP/PU nanocomposites increased by 4 times and the fracture toughness by nearly 3 times.This individualized phenomenon was attributed that the abundant covalent bonding between PDA-GNP and PU resulted in strong interfacial interactions and good compatibility specifically associated with the changes of PU hard microdomains.The tensile strength of PDA-GNP/PU was still was still superior to that of pure PU under high-energy ionizing irradiation.In this paper,the evolution of the microstructures of polyurethane elastomers in the high-energy irradiation environment was systematically and comprehensively studied,and the deterioration of the mechanical properties was explained from the perspective of microstructures.Furthermore,the mechanism of the polydopamine and graphene free radical scavengers on the improvement of irradiation resistance of polyurethane elastomers was revealed.This method can provide a new idea for the irradiation resistance design of other kinds of polymer materials.