ポリビニルアルコールの部分および高度フォルマール化物の応力緩和挙動 : 高分子レオロジー

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The stress relaxation behavior of partly to highly formalized polyvinyl alcohol polymers has been investigated over ranges of time scale from 10 to 7000 seconds and of temperature from 80 to 160℃, in order to obtain informations about the effects of succesive changes in the polymer structure from quasi-crystalline to amorphous state upon the temperature dependence of the relaxation processes. The results obtained are summerized as follows : (1) The so-called master relaxation curve can be composed without difficulty from relaxation curves at various temperatures by using the ordinary time-temperature superposition method, but the temperature dependence of the shift factor log a_T above the glass transition temperature is no longer expressed by the simple WLF equation, but by a combination of at least two WLF type equations. (2) The temperature dependence of the apparent activation energy for the relaxation process evaluated from the shift factor shows not only an extreme maximum at the glass transition temperature T_g as observed for many other amorphous polymers, but also another small maximum at the higher temperature than T_g. With the increase of the degree of formalization, the temperature T_g becomes higher while the maximum activation energy (ΔH_a)_<max> at T_g becomes smaller except for an unusually large (ΔH_a)_<max> for PVF-80. The existence of the small maximum, which disappears with increasing degree of formalization, corresponds to that of the second temperature dispersion of the dynamic modulus which is observed at a temperature T_<g2>'' higher than the glass transition temperature T_g'' under a constant frequency of 3×10^<-3> cps. The anomaly of the temperature dependence of the shift factor revolting from the simple WLF equation correlates with the existences of the small maximum on the apparent activation energy and of the second temperature dispersion on the dynamic modulus and may suggest the existence of another type of relaxation process. (3) The relaxation spectrum for each polymer has been obtained from the master curve by using the customary method of Swarzl-Staverman's 2nd approximation. With decreasing degree of formalization the relaxation spectrum at a reference temperature of 110℃ not only shifts to shorter times but also changes the shape systematically in such a way as decreasing the slope of the wedge portion, increasing the height as well as the width of the box portion and revealing a new bump in the middle of the wedge portion. The new bump may correlate with the anomaly of temperature dependence of the shift factor due to the existence of another type of relaxation process mentioned above. It is hoped that the new bump is separated from the apparent relaxation spectrum.
社団法人日本材料学会の論文
1961-05-15

ポリビニルアルコールの部分および高度フォルマール化物の応力緩和挙動 : 高分子レオロジー

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