Water effect on the morphology of EVOH copolymers

✍ Scribed by Susana Aucejo; Carlos Marco; Rafael Gavara

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 144 KB
• Volume: 74
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19991031)74:5<1201::aid-app17>3.0.co;2-8

✦ Synopsis

The effect of water on the morphology of four ethylene vinyl alcohol copolymers (EVOH) with different ethylene contents was studied by differential scanning calorimetry (DSC). EVOH film samples equilibrated in controlled atmospheres at different relative humidities (RH) and 23°C were analyzed. Under dry conditions, the glass transition temperature (T g ) was unaffected by copolymer ethylene content. As RH increases, T g decreases. It seems that the presence of water within the polymer matrix results in plasticization of the polymer. T g varies from around 50°C (dry) to below room temperature. EVOH copolymers are glassy polymers when dry and rubbery polymers at high RHs. Fox and Gordon-Taylor's equations well describe T g depletion at low water uptake, although severe water gain results in a considerable T g decrease, which is not predicted by these theories. Melting temperature, T m , and enthalpy, ⌬H m , were also analyzed. When dry, T m decreases as ethylene content increases. No significant water effect was found on either T m or ⌬H m . Hence, crystallinity seems to be unaffected by water presence.