フェノール樹脂・ポリビニルブチラール系の力学的緩和と誘電的緩和
1963 年 12 巻 116 号 p. 395-399
詳細
1963 年 12 巻 116 号 p. 395-399
The tensile stress relaxation behavior of the phenol resin-polyvinyl butyral (PVB) system, varying the PVB content in the system, was investigated at various temperatures above the glass transition temperature of PVB in order to compare it with the dielectric relaxation behavior. Mechanical and dielectric relaxation spectra were obtained from the so-called master relaxation curve found by shifting relaxation curves measured at various temperatures over to reference temperature 131°C, on the basis of the hypothesis of time-temperature superposition.
Applicability of the two shift factors, i.e. aT for tensile stress relaxation and bT for dielectric relaxation, to the WLF-equation was checked by means of a straight-line relationship between (T-T0)//logaT and T for all the specimens employed herein.
When checking the results on the tensile stress relaxation process, existence of two segments of straight lines were observed at the temperature ranges from 110 to 130°C and from 135 to 151°C respectively. Moreover, the temperature dependence of the apparent activation energy during the relaxation process evaluted from the shift factor aT showed two peaks at the foregoing temperature ranges. The peak at the lower temperature range, which may be due to the second transition of PVB contained in the system, corresponds to the dielectric dispersion in α range from 90 to 140°C.
The two shift factors are identical for the specimens of the PVB contents ranging from 60 to 80%, but the mechanical and dielectric relaxation spectra are of very different shape. In addition, the maximum in the mechanical relaxation spectrum is, for each specimen, at a much longer time than the maximum in the dielectric one.
From the results of the check mentioned above, the WLF-equation holds fairly well for the specimens of the PVB contents ranging from 20 to 80% in the case of the dielectric relaxation process, but it does not hold for the specimens under 40% PVB content in the case of the mechanical relaxation process.
It is therefore concluded that mechanical and dielectric relaxation behavior of polymers must be related, since they involve configurational changes of flexible molecules, and also that mechanical relaxation behavior may be strongly influenced by a distribution of effective chain length, whereas dielectric one would not be so much.
