Shigetoshi Ikeda

Chemical structure and physical properties of radiation-induced crosslinking of polytetrafluoroethylene

Abstract The chemical structure and physical properties of polytetrafluoroethylene (PTFE) that has been crosslinked by radiation have been studied by various methods. It has been found that a Y-type crosslinking structure and a Y-type structure incorporating a double bond (modified Y-type) is formed in PTFE by radiation-crosslinking in the molten state. In addition, various types of double bond structures, excluding the crosslinking site, have been identified. The crosslinked PTFE has a good light transparency due to the loss of crystallites, whilst it retains the excellent properties of electrical insulation and heat resistance. The coefficient of abrasion and the permanent creep are also greatly improved by crosslinking.

Study on poly-electrolyte membrane of crosslinked PTFE by radiation-grafting

Abstract Polymer electrolyte fuel cell membrane based on crosslinked polytetrafluoroethylene (PTFE) [RX-PTFE] has been processed by radiation-grafting with reactive styrene monomers by γ-rays under atmospheric circumstances, and the characteristic properties of the obtained membranes have been studied. The grafting yields of styrene monomer onto RX-PTFE, which have various crosslinking densities, were in the range of 5–100%. At the reaction period of 24 h, the grafting yields for RX-PTFE with low crosslinking density, which was reacted at 60 °C, achieved 94%. As a tendency, the lower grafting temperature gives higher grafting ratio of styrene onto RX-PTFE. Moreover, the yields of subsequent sulfonation for all samples were close to 100%. Mechanical properties were decreased with increasing grafting yields; especially the membrane with higher grafting yields was brittle. Ion exchange capacity of sulfonated RX-PTFE reached 1.1 meq/g while maintaining the mechanical properties.

Radiation-induced crosslinking and grafting of polytetrafluoroethylene

Radiation-induced crosslinking and grafting of poly(tetrafluoroethylene) (PTFE) and chemical structures of their products have been investigated. It has been found that the crosslinking of PTFE can be formed not only by irradiation in the molten state, but also by multiple (stepwise) grafting of the monomer onto PTFE.

Electron‐induced crosslinking of polypropylene with the addition of hydrogen‐donating hydrocarbons

Electron-induced crosslinking of polypropylene with the addition of hydrogen-donating hydrocarbons produced from petroleum (HHAP) together with A-TMPT (trimethylpropanetriacrylate) was studied, and the following results were obtained: (1) Effective crosslinking was achieved at lower doses under 10 kGy. (2) HHAP functions as an effective radical scavenger to suppress scissions. (3) Distinguished improvements in properties such as elongation and heat distortion temperature were achieved by the irradiation. (4) Distinct diminution in melt flow rate and evident increase in average molecular weight with the irradiation at lower doses were observed. (5) It was confirmed that the oxidative degradation during mixing and molding was noticeably inhibited by the addition of HHAP. This effect as an antioxidant during these procedures along with the irradiation seems to be a cause to promote crosslinks. These effects are attributable to the high radical scavenging effects of HHAP and its pure hydrocarbon constitution without functional groups containing heteroatoms.

Micromachining of crosslinked PTFE by direct photo-etching using synchrotron radiation

Micromachining of crosslinked PTFE (polytetrafluoroethylene) using synchrotron radiation direct photo-etching method has been demonstrated. High aspect-ratio microfabrication was carried out. The etching rate of crosslinked PTFE was higher than that of non-crosslinked PTFE. Through the etching rate measurements of various samples, it was found that synchrotron radiation etching rate of crosslinked PTFE only depends on the degree of crosslinking, neither molecular weight nor crystallinity. The effect of molecular motion on etching process was discussed from temperature dependence data on etching rate. Furthermore, the surface region of synchrotron radiation irradiated sample was investigated by Fourier transform infrared spectroscopy and the experimental result showed that the modification induced by synchrotron radiation proceeded before desorption.

Fabrication of a poly-electrolyte membrane based on cross-linked PTFE thin film by EB irradiation grafting

Polymer electrolyte fuel cell (PEFC) membranes based on cross-linked polytetrafluoroethylene (RX-PTFE) very thin film have been fabricated by radiation grafting with reactive styrene monomers using electron beam irradiation under nitrogen atmosphere at room temperature. The characteristic properties of obtained materials have been measured by differential scanning calorimetry, thermogravimetric analysis, FT-IR spectroscopy, etc. The glass transition temperatures and thermal decomposition temperatures of grafted materials strongly depend on the yields of styrene grafting onto base materials. The higher yields of grafting give lower thermal stability. The ion-exchange capacity of sulfonated materials is 3.0 mEquiv/g. The other properties of obtained membranes, such as chemical structure and rates of hydrogen gas transmission, are discussed.

Surface modification of polytetrafluoroethylene by synchrotron radiation

Abstract Surface modification of polytetrafluoroethylene (PTFE) films by the irradiation using synchrotron radiation (SR) below the melting temperature was studied. The changes in chemical structures, surface compositions and thermal properties of the SR-irradiated PTFE were examined by solid-state 19F NMR, X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC), respectively. In order to investigate the degree of modification as a function of depth from the irradiated surface, some PTFE thin films were stacked in layers under vacuum and then they were irradiated with SR. It was found that crosslinking reaction was induced by SR-irradiation in the solid-state within 50 μm from the exposed surface and chain scission was dominant at deeper layers.

High-aspect-ratio microfabrication of crosslinked polytetrafluoroethylene using synchrotron radiation direct photo-etching

High-aspect ratio micro-fabrication of crosslinked polytetrafluoroethylene (PTFE) has been carried out using synchrotron radiation (SR) direct photo-etching. The etching rates of crosslinked PTFE samples with various crosslinked densities were studied by changing photon fluence of SR at different sample temperatures. The maximum etching rate of 150 micron/min was achieved at SR beam current of 600 mA. The etching rate of the sample with higher crosslinking density resulted in a higher etching rate. This rate was about two times higher than that of non-crosslinked PTFE. The effects of molecular motion and fragmentation of the molecules on etching process were discussed from temperature dependence on etching rate. Furthermore, we have found that surface modification of non-crosslinked PTFE had been proceeding during irradiation of SR to the surfaces at 140 °C. The modified surfaces were examined on behavior of crystallites by differential scanning calorimetry, and on chemical structure by FTIR spectroscopy and solid-state F NMR spectroscopy. The results showed that properties of modified layers have dependence on depth. Crosslinking reaction would be induced by SR irradiation even in its solid state within about 50 μm from the surface.