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Water effect on the morphology of EVOH copolymers
Author(s) -
Aucejo Susana,
Marco Carlos,
Gavara Rafael
Publication year - 1999
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/(sici)1097-4628(19991031)74:5<1201::aid-app17>3.0.co;2-8
Subject(s) - differential scanning calorimetry , crystallinity , copolymer , glass transition , polymer , materials science , polymer chemistry , ethylene , plasticizer , chemical engineering , enthalpy , morphology (biology) , chemistry , composite material , organic chemistry , thermodynamics , catalysis , physics , genetics , biology , engineering
Abstract 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, Δ 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 Δ H m . Hence, crystallinity seems to be unaffected by water presence. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1201–1206, 1999