Effect of Gamma Irradiation on Structure and Tribological Properties of PTFE Composites

In this paper, the tribological behavior of PTFE and its composites after gamma ray irradiation was studied. The effects of irradiation on the chemical structure, heat resistance and tensile properties of the materials were mainly investigated, so as to establish the correlation between the structure change and tribological properties of PTFE under irradiation, and provide guidance for the design of PTFE sealing materials for nuclear power plants. Poly (phenylene terephthalate) modified polytetrafluoroethylene (PTFE/POB) composites were irradiated by gamma-ray with dose of 1000 Gy, 1500 Gy, 2200 Gy, and 3000 Gy. The chemical composition and crystal structure of the materials before and after irradiation were characterized by infrared spectroscopy, X-ray diffraction and differential scanning calorimetry. The thermal stability, tensile properties and tribological properties of the materials were compared with those of irradiated pure PTFE. The results show that the chemical composition and thermal stability of PTFE/POB materials are not significantly changed under irradiation, but the molecular weight of PTFE decreases sharply, and the small molecular chains spontaneously form crystalline phase, leading to the increase of crystallinity. Compared with pure PTFE, the addition of POB improves the radiation resistance of PTFE to a certain extent, and delays the decrease of molecular weight and recrystallization ability of PTFE. The results showed that the tensile strength of PTFE and PTFE/POB decreased significantly after irradiation, but for PTFE/POB, with the increase of irradiation dose, the decreasing trend of the tensile strength of PTFE/POB was not significant, but gradually stabilized. The effect of irradiation on the elongation at break of PTFE and PTFE/POB is complex. The elongation at break of pure PTFE increases first and then decreases with the increase of irradiation dose, while the elongation at break of PTFE/POB decreases with the increase of irradiation dose. The effect of irradiation on the wear resistance of PTFE/POB is not significant, but the friction coefficient decreases to some extent. With the increase of irradiation dose, the friction coefficient first increases and then decreases. This is mainly because with the continuous increase of irradiation dose, the molecular chain length of PTFE becomes shorter and the size of crystal band becomes smaller, leading to the obvious increase of the grain boundaries. It results in the increase of shear strength gradually, leading to the increase of friction coefficient.