Study On Poly (Tetrafluoroethylene) Aqueous Dispersion Irradiated By Gamma Ray And Preparation Of Fluorocarbon Finishes

In this paper, polytetrafluoroethylene aqueous dispersion irradiated by gamma ray and Preparation of fluorocarbon finishes by γ-radiation induced emulsion polymerization were both studied.Polytetrafluoroethylene (PTFE) has attracted wide attention for its excellent properties such as low friction coefficient, non-wetting property, high thermal and chemical resistance. However, PTFE is highly sensitive to radiation and its molecular weight (M_n) decreases rapidly with radiation dose. Upon irradiation by electron beam or y rays, the chemical structure, morphology and molecular weight of PTFE change considerably depending on the factors including dose rate, dose range, temperature, oxygen content, etc. The mechanism of radiation-induced degradation of PTFE has been extensively studied. PTFE predominantly undergoes chain scission when irradiated at room temperature in air and vacuum.The motivation of this work is to investigate in detail the radiation induced degradation of PTFE in dispersion. Radiation effects on molecular weight, crystallinity, medium pH, size and morphology of PTFE particles were studied over a wide dose range.The change in property of PTFE was characterized by photon cross correlation spectroscopy (PCCS), scanning electron microscopy (SEM),X-ray diffraction (XRD), FT-IR spectroscopy and X-ray photoelectron spectroscope (XPS), differential scanning calorimetry (DSC) et al. It was found that the mean particle size of PTFE reduces from 250 run of the control to 170 nm at 100 kGy, as confirmed by dynamic laser scattering and SEM. The crystallinity degree of PTFE increased at 20 kGy but remained unvaried at higher dose level. G-value of scission, G (s), was determined to be 0.46 umol/J.Crystallization of poly (tetrafluoroethylene) was also observed by DSC at constant cooling rates. We used Ozawa equation to describe the nonisothermal crystallization. The result shown the process is complicated maybe caused by different molecular weight of samples and the limits of Ozawa's theory.In the second part of the paper, Fluorocarbon finishing agents were prepared by y-ray initiated emulsion polymerization of fluorine-containing acrylates at different doses. Copolymerization of the fluorocarbon monomer and butyl acrylate was also studied. Morphology and size distribution of the emulsion particles were investigated by transmissionelectron microscopy and dynamic light scattering,__respectively. Influence offluorine-containing monomer on water and oil repellency property of final products was discussed. It was found that conversion of the dodecafluoroheptyl methacrylate was 98 % at...