The effect of water on the morphology of four ethylene vinyl alcohol copoly
mers (EVOH) with different ethylene contents was studied by differential sc
anning calorimetry (DSC). EVOH film samples equilibrated in controlled atmo
spheres at different relative humidities (RK) and 23 degrees C were analyze
d. Under dry conditions, the glass transition temperature (T-g) was unaffec
ted by copolymer ethylene content. As RH increases, T-g decreases. It seems
that the presence of water within the polymer matrix results in plasticiza
tion of the polymer. T-g varies from around 50 degrees C (dry) to below roo
m temperature. EVOH copolymers are glassy polymers when dry and rubbery pol
ymers at high RHs. Fox and Gordon-Taylor's equations well describe T-g depl
etion at low water uptake, although severe water gain results in a consider
able T-g decrease, which is not predicted by these theories. Melting temper
ature, T-m, and enthalpy, Delta H-m, were also analyzed. When dry, T-m, dec
reases as ethylene content increases. No significant water effect was found
on either T-m or Delta H-m. Hence, crystallinity seems to be unaffected by
water presence. (C) 1999 John Wiley & Sons, Inc.