Comparing dielectric measurements on poly(ethylene terephthalate) at constant heating rates with isothermal measurements

In this study, dielectric relaxation spectroscopy experiments were carried out during heating in the alpha relaxation region of PET. The results for l ow heating rates were consistent with isothermal measurements. Moreover, th e results expressed as a function of temperature were much clearer than tho se expressed as a function of frequency. However, the loss peaks obtained i n these non-isothermal experiments showed a systematic shift on the tempera ture axis when the heating rate increased. A significant but nearly constan t thermal lag was observed in experiments with heating at 1 K min(-1) when using different equipment. It appears that isothermal data obtained in a we ll calibrated apparatus can be used to adjust the temperature axis of diele ctric results obtained in ramp temperature experiments. (C) 1999 Elsevier S cience Ltd. All rights reserved.