Viscoelastic Behavior of Polytetrafluoroethylene in the Neighborhood of the Crystalline Transition Temperature
1966 Volume 15 Issue 152 Pages 331-334
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1966 Volume 15 Issue 152 Pages 331-334
The dynamic mechanical properties of polytetrafluoroethylene (PTFE) at various frequencies were measured by means of three sorts of vibrations, the torsional free vibration, the bending vibration of rectangular bars freely suspended or fixed on one end, and the longitudinal vibration. The results are compared with those of other authors in the neighborhood of the crystalline transition temperature.1)3)∼9)A broad absorption exists with the low frequencies between the temperatures of the primary absorption (β')1)2) and crystalline transition (about 20∼30°C). The result indicates the necessity of scrutiny of the so called β dispersion region.
In Figs. 1, 2, 3and 4 are shown the results of measurement of low density sperimen (2.163g/cm3 at 19°C) at various frequencies. In Fig.1, the broad absorption is at about 8°C, which is not in the mechanical data of other authors. The comparison of temperature variation of loss modulus at various frequencies shows that the broad absorption at low frequency is shifted to the higher temperatures with increasing frequency. The relaxation map (Fig. 6) is made by plotting the frequency of maximum loss against the reciprocal absolute temperature in the neighborhood of crystalline transition and the primary dispersion temperatures. This figure is different from the mechanical relaxation map of other authors.1)10) The broad absorption of low density specimen in this figure can be connected with the crystalline dispersion at higher temperatures with increasing frequency. The value of apparent energy of activation of the broad dispersion mechanism was obtained as 27kcal/mole, the value being consistent with that of the primary absorption. It appears in this way that the broad absorption in PTFF comes from the same absorption mechanism as that of the grain-boundary dispersion observed in polyethylene, 11)12) since the broad line component of NMR absorption line does not show narrowing at a temperature above crystalline transition.13)
