Internal friction behavior near the crystalline phase transition temperatures for as-polymerized polytetrafluoroethylene

Viscoelastic properties of polytetrafluoroethylene (PTFE) have been investigated over a wide temperature range at different frequencies. The results of mechanical dispersion studies for PTFE indicated that there are three relaxation regions, denoted alpha , beta , and gamma in order of decreasing temperature, and two crystalline phase transitions at 293 and 303K. In addition, the degree of crystallinity of as-polymerized PTFE has been estimated by use of different methods. The experimental results of density, infrared, X-ray, and nuclear magnetic resonance (NMR) measurements gave a high degree of crystallinity, above 90%. The morphology of an as-polymerized PTFE sample suggested that the particle structures, as seen in electron micrographs, are formed by the overall folding of the extended chain lamellae to the longitudinal direction of which chains are arranged parallel to each other. Torsional pendulum measurements were carried out at temperatures between 95 and 400K at a low measuring frequency, nominally 0.5 Hz. Braids of glass filaments were used as supports of PTFE emulsion particles, which originally had been dispersed in water. The composite specimen was annealed at about 430K for more than two days to remove water and surfactants. The measurement of the torsional pendulum was run at slow rates of 1-2K/min at an atmosphere of flowing dry nitrogen.--AA