Mechanical Behavior And Damage Mechanism For Cross-linked Polytetrafluoroethylene Irradiated By Gamma Rays

Polymers in the field of strong radiation fields(such as space environment,communication,and nuclear reactors,etc.)will inevitably be exposed to radiation from charged particles such as electrons,protons,and heavy ions,which will induce a large number of free radicals in polymers and in turn cause changes such as molecular chain breakage and cross-linking of polymeric materials,affecting their stability and lifetime during service.In this paper,the thermal properties of XPTFE were evaluated.Besides,the uniaxial tensile deformation behavior of XPTFE with different crosslinking degrees was evaluated by using synchrotron ultra-small angle X-ray scattering(USAXS)technique combined with in situ uniaxial stretching to study the microstructural evolution of XPTFE with different crosslinking degrees under different strains.The evolution and decay behavior of free radicals generated in irradiated XPTFE were investigated using electron spin resonance(ESR)to reveal the radiation damage mechanism of XPTFE charged particles.The microstructural evolution of XPTFE with different crosslinking degrees at different absorbed doses was analyzed using USAXS,and the tensile deformation behavior of XPTFE after irradiation was investigated.The main conclusions are as follows.(1)For XPTFE cross-linked by irradiation at high temperature,its tensile strength decreased by nearly 22%,the elongation at break decreased by about 77%,and the hardness increased by approximate 40%.the cross-linking degree of XP TFE increased with absorbed doses.During the in situ uniaxial stretching of XPTFE at lower strains,what mainly occur were the tilting of molecular chains and the rotation and slippage of lamellar crystals along the stretching direction.(2)Three kinds of radicals,namely,alkyl radicals,chain end radicals and tertiary alkyl radicals,will be generated in XPTFE irradiated by γ-rays.Under the same irradiation conditions,the concentration of free radicals in XPTFE increases with the increase of cross-linking degree.The chain-end radicals are more sensitive to oxygen than the intermediate chain alkyl radicals and are more easily oxidized to peroxy radicals.(3)The chemical structure changes of XPTFE after irradiation are small.With the increase of absorbed dose,XPTFE firstly undergoes the breakage of crosslinking sites,followed by the breakage of molecular chains.XPTFE with high absorbed doses showed a loss of mechanical properties due to the breakage of cross-linkage points and molecular chains.During uniaxial stretching of irradiated XPTFE at room temperature,some small crystals were oriented along the stretching direction and with the formation of voids.Compared with PTFE,XPTFE has enhanced irradiation resistance and is expected to be widely used in aerospace and nuclear reactor environments where strong radiation fields are present.The study of the structural evolution of the tensile deformation behavior of XPTFE and the evolution of its radicals after irradiation is helpful to evaluate the service behavior and failure mechanism of the material,which is of great significance to the integration of the theory and engineering practice of XPTFE.Figure [47] Table [7] Reference [101]...