Water sorption in amorphous poly(ethylene terephthalate)

✍ Scribed by A. Launay; F. Thominette; J. Verdu

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 160 KB
• Volume: 73
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19990815)73:7<1131::aid-app4>3.0.co;2-u

✦ Synopsis

The water sorption characteristics of poly(ethylene terephthalate) (PET) amorphous samples of 250 m thickness have been studied at various temperatures in a saturated atmosphere. Concerning diffusivity, one can distinguish the following two domains characterized by distinct values of the activation energy: E D Ϸ 36 kJ mol Ϫ1 at T Ͼ 100°C, and E D Ϸ 42 kJ mol Ϫ1 at T Ͻ 60°C, with a relatively wide (60 -100°C) intermediary domain linked to the glass transition of the polymer. The crystallization of this latter occurs in the time scale of diffusion above 80°C but doesn't change the Fickian character of sorption curves. The equilibrium concentration m ϱ is an increasing function of temperature, but the solubility coefficient S decreases sharply with this latter, with the apparent enthalpy of dissolution ⌬H s being of the order of Ϫ28 kJ mol Ϫ1 at T Ͻ 80°C and Ϫ45 kJ mol Ϫ1 at T Ͼ 80°C. Density measurements in the wet and dry states suggest that water is almost entirely dissolved in the amorphous matrix at T Ͻ 80°C but forms partially a separated phase at T Ͼ 80°C. Microvoiding can be attributed to crystallization-induced demixing.