ON THE AGING CHARACTERIZATION OF POLY(ETHYLENE-TEREPHTHALATE) BY POSITRON SPECTROSCOPY

Positron spectroscopy was used to study the free volume properties of glassy poly(ethylene terephthalate) as a function of temperature and a ging time. The experimental results indicate that the glass transition temperature increases with increasing aging time. This is confirmed b y differential scanning calorimetry measurements. From the aging time dependence of the intensity of the ortho-positronium (o-Ps) component I-3 and the fractional free volume, we observe that the concentration of free volume holes and the fractional free volume show a continuous decrease at a fixed aging temperature, which suggests that structural relaxation and segmental rearrangement occur during physical aging. (C ) 1997 Elsevier Science B.V.