Dynamic mechanical properties of polyethylene terephthalate

Abstract

Abstract Dynamic mechanical properties of polyethylene terephthalate have been measured as function of temperature at −70 to +310°C. at 100–200 cycles/sec. by a cantilever vibration method. Two mechanical loss maxima have been distinguished, and effects associated with variations in the degree of crystallinity and orientation and in the water content of the material have been investigated. The main softening region is shown to be influenced by the variations in the degree of crystallinity. Another process, which occurs at low temperature, is affected by changes in the water content of the material. The height of the loss maximum is increased when water is absorbed, although the temperature at which maximum loss occurs remains unchanged. Finally, the low temperature process is compared for members of a series of polyesters. Increasing the distance between the cyclic groups brings about a slight reduction in the temperature of this loss maximum. Interchange of the positions of the magnified image and O groups depresses the loss maximum temperature.