Equation-of-state properties and surface tension of ethylene–vinyl alcohol random copolymers

Pressure–volume–temperature (PVT) data were studied for ethylene–vinyl alcohol random copolymers (EVOH) and served to determine bulk reduction parameters for the equation-of-state by Flory–Orwoll–Vrij. The compressibility factor as a function of copolymer composition displays positive deviation from additivity. Sessile drop method yielded surface tensions of EVOH melts at different temperatures. To a good approximation linear variation of surface tension with respect to copolymer composition was observed. It indicates that conformational restrictions prevent surface excess of the low-energy units. Results on surface tensions are discussed in terms of different theoretical approaches. It turns out that the parachor approach is in excellent agreement with experimental data. The corresponding state approximation revealed decreasing surface energy with ascending ethylene content whereas the surface entropy remains approximately constant as long as vinyl alcohol units are in excess.