Sorption and diffusion of water vapor in poly(ethylene terephthalate) film

Abstract

ABSTRACT:The sorption and diffusion of water vapor in poly(ethylene terephthalate) (PET) film were measured by applying a thermogravimetric analyzer (TG-DTA), which customarily has been used to detect the weight loss of a sample with the increase of temperature under a given atmosphere. In this case, we detected the weight gain of PET film by sorption of water vapor under a given humidity at a constant temperature. Sorption-rate curves were successfully obtained in spite of the low solubility of PET film and the presence of Fickian-type curves. The solubility was better described according to the dual-mode sorption model. The diffusion coefficients were determined in their initial slopes by the short-time method. We found that the diffusion coefficient depended on vapor pressure.

Permeation of water vapor through high performance laminates for VIPs and physical characterization of sorption and diffusion phenomena

“…(10)) considering the range of pressure covered. Very good agreements are observed for PET with the results from Shigetomi [20] and Yasuda and Stannett [21]; this concerns the values and the very good reported match with Henry's law [21]. For the first one, this agreement is in fact a little bit trickier because two opposite factors influence the value:…”

“…Another interesting point to note is that Shigetomi [20] finds like us a slight influence of the humidity on the diffusion coefficient of water vapor in crystallized PET.…”

“…-on the one hand the low pressure (2000 Pa) considered by Shigetomi [20] leads to an overestimation of the global solubility coefficient due to the role of the Langmuir adsorption mode neglected in the present work done at higher pressure; -on the other hand, the very high crystallinity of PET studied by Shigetomi leads to a lower solubility coefficient.…”

“…Table 11 compares the main results with the bibliographic data [20,21,24,25]. The values must be compared taking into account the crystallinity, as the diffusion coefficient varies greatly with it, in the following equation [25].…”

“…The temperature dependence is expressed by the activation energy Q D , found equal respectively to 36 and 43 kJ mol −1 by Shigetomi [20] and Yasuda and Stannett [21], which can be compared to the mean value of 54 kJ mol −1 obtained in the present work on metalized PET. Another interesting point to note is that Shigetomi [20] finds like us a slight influence of the humidity on the diffusion coefficient of water vapor in crystallized PET.…”