Degradation Behaviors And Damage Mechanism Of Shape Memory Epoxy Resin Under Electron/Proton Irradiations

As a novel type of smart material,shape memory polymers(SMPs)can fix the initial shape under specific conditions and return to the initial shape through external stimuli such as heat,light,and electricity and so on.With the advantages of low density,low processing cost,self-controllable expansion,and large shape transition temperature range,SMPs have great application potential in the fields of aerospace,biomedicine and smart molds.Based on the application of shape memory polymers in the space environment,this paper takes shape memory epoxy resin(SMEP)as the research object.With the dynamic thermomechanical analyzer,the shape memory performance of shape memory epoxy resin before and after irradiation was evaluated automatically in term of shape fixity ratio and shape recovery ratio,resulting from a four-step thermomechanical loading-unloading cycle(loading at high temperature,cooling while load retention,unloading at low temperature,heating recovering).And the degradation behaviors and damage mechanism of shape memory epoxy resin under electron irradiation,proton irradiation,proton and electron combined irradiation have been systematically studied in this paper from the viewpoint of dynamic thermomechanical analysis,Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy and electronic paramagnetic resonance analysis,etc..After electron irradiation,the shape fixity ratio of SMEP remained almost unchanged while the shape recovery ratio decreased.And the degradation of shape recovery ratio after 1 Me V electron irradiation was more serious than that after 170 ke V electron irradiation.After 170 ke V and 1 Me V electron irradiation,the rubbery storage modulus decreased,and the glass transition temperature decreased as the electron irradiation fluence increased.Electron irradiation mainly destroyed weak aliphatic bonds such as C-N bonds and C-O bonds of shape memory epoxy resins,forming active nitrogenous free radicals and phenoxy-type free radicals.These chain scissions mainly occurred near the netpoints or at the branches and chain segments.After the C-N bonds were destroyed by 1 Me V electron irradiation,nitrogenous free radicals were formed first,eventually evolving into nitrogen oxides and nitr ogen hydrides.After the C-N bonds were destroyed by 170 ke V electron irradiation,only nitrogenous free radicals were detected.The oxygen in the atmosphere can oxidize these primary free radicals and form peroxy free radicals,which can aggravate the propagation of chain scission and generate new chain ends and new free radicals.After proton irradiation,the shape fixity ratio of shape memory epoxy resin remained almost unchanged while the shape recovery ratio decreased seriously.Under the same energy and fluence,the degradation of shape recovery ratio of shape memory epoxy resin after proton irradiation was more severely than that after electron irradiation.In addition,the glassy storage modulus decreased after 170 ke V and 1Me V proton irradiation,and the rubbery storage modulus increased,which was significantly different from that after electron irradiation.After 170 ke V proton irradiation,the glass transition temperature decreased with the increase of the irradiation fluence,while there was "multi-peaks" newly appeared in the loss modulus spectra and the loss factor spectra of shape memory epoxy resin after 1 Me V proton irradiation.Proton irradiation not only destroyed the C-N bonds and C-O bonds of shape memory epoxy resin,but also destroyed the C-C bonds.These scissions not only occurred near the netpoints,but also occurred mainly at the macromolecular chains,generating new segments.After 170 ke V and 1 Me V proton irradiation,only pyrolytic carbon radicals were detected while nitrogenous free radicals and phenoxytype radicals were not detected.The concentration of pyrolytic carbon radicals increased and then stabilized with the increase of the irradiation fluence.After 170 ke V proton and electron combined irradiation,the shape fixity ratio of shape memory epoxy resin remained almost unchanged,and the shape recovery ratio decreased.The degradation of the shape recovery ratio after 170 ke V proton and electron combined irradiation was lower than that after 170 ke V proton irradiation,but was higher than that after 170 ke V electron irradiation.The glassy storage modulus decreased after 170 ke V proton and electron combined irradiation,and the rubbery storage modulus increased,which was similar to the results after 170 ke V proton irradiation,but different from the results after 170 ke V electron irradiation.170 ke V proton and electron integrated irradiation not only destroyed the C-N bonds near the crosslinking point of shape memory epoxy resin,but also destroyed the C-O bonds and C-C bonds in the macromolecular chains,producing many new segments.After 170 ke V proton and electron combined irradiation,nitrogenous free radicals,phenoxy-type radicals and pyrolytic carbon free radicals were detected,which were similar to the results after 170 ke V electron irradiation.The difference was that nitrogenous free radicals and phenoxy-type free radicals disappeared quickly with the increase of the irradiation fluence.The coupling effects of 170 ke V proton and electron combined irradiation was weakened,because there was a certain degree of cross-linking between the oxirane group and the hydroxyl group.