Water absorption in EVOH films and its influence on glass transition temperature

Moisture sorption kinetics of nonoriented ethylene vinyl alcohol copolymer (EVOH) film (EF-E15) were studied at 25, 35, and 45 degrees C. Anomalous di ffusion was observed for the polymeric film at high relative humidities (RH ) and higher temperatures. Diffusion and solubility coefficients of water w ere found to be concentration dependent. The moisture sorption isotherms of three types of EVOH films (EF-E15, EF-F15, and EF-XL15) determined at 25, 35, and 45 degrees C, were well described using the GAB equation. Glass tra nsition temperatures (T-g) of the EVOH films, as influenced by RH, were mea sured using differential scanning calorimetry. T-g values decreased with in creasing RH due to the plasticization effect of water, and were found to be dependent on ethylene content and orientation of the EVOH films. (C) 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 691-699, 1999.