The Coupling Effect Of Stress/charged Particle Irradiation On Polyimide Fibers

Polyimide fibers have been widely used in the aerospace field due to their excellent properties such as high temperature resistance,low temperature resistance,high strength and high modulus,creep resistance and radiation resistance,etc.However,polyimide fibers will be damaged by electron,proton irradiation,especially under stress conditions during their application in space environment.In order to explore the performance changes of the polyimide fiber and the damage mechanism after irradiation,this paper studies the changes of the mechanical properties and molecular structure of different types of polyimide fibers irradiated with different fluences of protons and electrons,respectively.The results showed that the tensile strength and elongation at break decreased with the increase of fluence,but the damage degree of Polyimide fibers with different structures was different.Under proton irradiation,the decrease rate of mechanical parameters of PI-3 is very small,and it has good resistance to proton irradiation.The decrease rate of tensile strength of PI-2 and Pi-4 is more than 10%,and the damage degree of PI-1is between them.Different from proton irradiation,the decrease rate of mechanical parameters of PI-2 after electron irradiation is very small,less than 2%.Compared with proton irradiation,the damage degree of PI-4 is also smaller,but the decrease rate is still about 10%.Comparing the differences between the effects of 170 ke V proton and 1 Me V electron on polyimide fibers,it is found that there is no obvious change in the surface morphology of the two kinds of irradiated polyimide fibers,but the difference was that the free radical type and content produced after irradiation..The free radical produced by proton irradiation was a pyrolytic carbon free radical,and the free radical produced by electron irradiation was hydrocarbon-based superoxygen free radical due to the participation of oxygen.The XPS analysis of the fiber after irradiation resulted in an increase in the carbon content of the fiber surface after proton irradiation,with a tendency towards graphite and a decrease in nitrogen content.The tensile strength and elongation at break of the polyimide fiber after stress coupled electron irradiation are slightly increased compared with those of single irradiation,but the mechanical damage of the polyimide fiber will be increased by stress coupled proton irradiation at higher fluence.The content of free radicals produced by proton irradiation at 5×10¹⁵cm^-2fluence is less than that produced by single irradiation,and the content of free radicals produced by stress coupled electron irradiation is also less than that produced by single irradiation.At the same time,the polyimide fibers were irradiated by stress coupled electron at a fluence of 5×10¹⁵cm^-2,the peak intensity of infrared spectrum decreases.One is the reaction of free radical produced by electron irradiation with oxygen,which hinders the recombination of free radical and original group.The other is the addition of stress increases the roughness of the fiber surface and enhances the surface scattering,which weakens the absorption peak.