Journal of Materials Science, Vol.37, No.22, 4861-4868, 2002
Preparation of ethylene vinyl acetate copolymer latex by flow induced phase inversion emulsification
Ethylene vinyl acetate (EVA) copolymer was emulsified in the melt state using hydrophobically modified water soluble polymers (HMWSPs) as surfactants and the flow induced phase inversion (FIPI) emulsification technique. The history of the emulsification and emulsion structure were monitored using a process rheometer and off-line scanning electron microscopy and particle size measurements. It was shown that low molecular weight surfactants could not be used to emulsify the polymer melt. When HMWSPs were used, the emulsion characteristics were strongly influenced by the molecular structure of the surfactant. Water-in-polymer melt emulsion was phase inverted to polymer melt-in-water emulsion at 20% water phase volume. When this emulsion was allowed to cool after further dilution (30% water) while mixing, a second phase inversion took place to obtain a water-in-polymer dispersion which has the consistency of a powder. When this dispersion was re-heated, while mixing, a third phase inversion occurred and a multiple emulsion system was obtained. Upon the solidification of the polymer, the structure of the dispersion was revealed as (water-in-polymer)-in-water. Water continuous latex from the first phase inversion and the powdery emulsion from the second phase inversion can be used in coating applications while the third phase inversion produces micro-porous polymer.