Emulsification, drying and film formation of alkyd emulsions

摘要

A method was developed and optimised for the emulsification of a conventional short oil alkyd resin which was solid at room temperature. The method was based on the emulsion inversion point (EIP) method whereby hot water (90 degreesC) was added to molten alkyd resin (90 degreesC) containing the emulsifier. Under slow mixing and addition of water, a point was reached where the emulsion instantaneously phase inverted from a water in oil emulsion (W/O) to an oil in water emulsion (O/W). Using optimum conditions, emulsions with droplet of diameters less than 0.8 mum were obtained. The drying and film formation of long oil alkyd emulsions were investigated with emphasis on loss of dry upon storage. The main reason for loss of dry was adsorption of the cobalt (drier) on pigment surfaces as a precipitated hydroxide. Titanium dioxides with alumina surface treatment and organic pigments were most detrimental to drying. Acrylate- and phosphate-based dispersants also deactivated cobalt presumably due to complexation and precipitation of cobalt. Emulsions prepared with an emulsifiable cobalt drier containing 2,2'-bipyridyl (complexing agent far cobalt) showed the best resistance to loss of dry. Films formed from the emulsions showed that surfactant migrated to the film surface which when washed with water leaves holes or pits in film. The pits were arranged in a hexagonal pattern, characteristic of Benard cells which form due to interfacial tension gradients generated in the film during evaporation of water. (C) 2000 Elsevier Science S.A. All rights reserved. [References: 15]