CALCULATION OF HIGH-PRESSURE PHASE-EQUILIBRIA OF MIXTURES OF ETHYLENE, VINYLACETATE AND AN (ETHYLENE-VINYLACETATE) COPOLYMER

Some new measurements of the high pressure demixing behaviour have been done in the system ethylene, vinyl acetate and an (ethylene-vinylacetate) copolymer. Calculations of phase equilibria using the chain-of-rotators equation of state are compared with these new experimental data. The miscibility gap of the ternary mixture can be predicted on the basis of a group contribution approach using interaction parameters from low molecular weight binary mixtures only. The model describe the phase separation (besides of polydispersity effects) sufficiently accurate up to high pressures. The derivation of the spinodal equation for ternary mixtures facilitates the calculation procedures applied. The model calculations detect a closed miscibility gap at higher pressures than in the binary subsystem composed of ethylene and the (ethylene-vinylacetate) copolymer. Experimental evidence for this behaviour is open, however.