Water effect on the morphology of EVOH copolymers

Abstract

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, ⌬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.

Immobilization of β-cyclodextrin in ethylene-vinyl alcohol copolymer for active food packaging applications

“…3 shows, the thermograms of the samples containing ␤CD present several differences with respect to the blank samples. The glass-transition temperature obtained for pure EVOH was 46 • C, in agreement with the T g values reported in the literature on this material [29,30]. The addition of 20% glycerol brought a reduction in the T g value of ca.…”

Influence of processing on the ethylene-vinyl alcohol (EVOH) properties: Application of the successive self-nucleation and annealing (SSA) technique

“…EVOH copolymers are widely employed in food packaging, biomedical and pharmaceutical industries because of their excellent barrier properties to gases, hydrocarbons and organic solvents [3,5]. Such properties are caused by strong hydrogen bond interactions, both inter and intra-molecular, which reduce the free volume of the polymer chains [6]. However, the barrier properties, stiffness or tensile strength, drop dramatically in high relative humidity conditions.…”

Water absorption and oxygen barrier characteristics of ethylene vinyl alcohol films

“…But the hydrophilic nature of EVOH is well known to compromise its barrier properties in humid environments (Zhang et al, 2001;Muramatsu et al, 2003). EVOH is capable of absorbing more than 10% by weight of moisture at equilibrium in saturated relative humidity (RH) environments or when immersed in water at room conditions (Aucejo et al, 1999). The presence of even small amounts of moisture in EVOH affect the oxygen barrier as well as their mechanical (Gaucher-Miri et al, 2002;Cabedo et al, 2006) and thermal properties (Aucejo et al, 1999;Zhang et al, 2001;Lagaron et al, 2001;Cabedo et al, 2006).…”

“…Data from Hernandez and Giacin (1998) also showed an increase in OTR by more than 60 times from 0.3 to 18.8 cc/m 2 day for PET/EVOH/PP film. The effects of moisture on polymer films containing EVOH are mainly attributed to plasticization of the EVOH matrix (Aucejo et al, 1999;Zhang et al, 2001;Muramatsu et al, 2003) and possible changes in polymer crystallinity (Hodge et al, 1996;Lopez-Rubio et al, 2005b). In this study, the effect of water absorbed during simulated retort heating on OTR was evaluated for two multilayer films containing EVOH.…”