A study of enthalpic relaxation of poly(ethylene terephthalate) by conventional and modulated temperature DSC

A standard power-compensation Perkin-Elmer DSC-2 was modified for temperatu re modulation experiments. Samples of amorphous poly(ethylene terephthalate ) were aged in the DSC at temperature, T-a, for time, t(a) below the amorph ous T-g. The progress of enthalpic relaxation was measured using convention al and modulated temperature DSC (MTDSC). By conventional DSC the extent of enthalpic relaxation was found to increase with ageing time accompanied by an apparent shift in the glass transition to a higher temperature. Using M TDSC the non-reversing enthalpic transition could be separated from the rev ersing glass transition. By MTDSC the extent of enthalpic relaxation was al so found to increase with ageing time. However, by studying the reversing c omponent it was found that there is no increase in the glass transition tem perature with increased ageing time. It was found that the kinetics of enth alpic relaxation were more accurately determined by conventional DSC than M TDSC. (C) 2001 Elsevier Science B.V. All rights reserved.