Ethylcellulose: a new type of emulsion stabilizer.

Cellulose ethers, in particular hypromellose, represent an interesting alternative when emulsions have to be stabilized avoiding conventional low molecular weight surfactants. So far this option has been only described for the formulation of oil-in-water (o/w) emulsions. Since surfactant-free water-in-oil (w/o) emulsions seem to be also attractive as drug carriers, ethyl cellulose, an oil-soluble cellulose derivative, was studied for its ability to stabilize w/o emulsions. Measurements of the interfacial tension confirmed that ethylcellulose was positively adsorbed at the water/oil interface with diverse lipids. Appearance of model emulsions was dependent on the processing temperature. At low temperatures (15 degrees C) cream-like o/w emulsions were obtained. Processing at 30 degrees C yielded fluid w/o-lotions. Investigation of the microstructure showed that the surface of the emulsion droplets was covered with particles which formed a mechanical barrier. These colloidal particles were shown to be a precipitate of ethylcellulose which forms when the polymer which was dissolved in the lipid phase comes into contact with water. Thus, ethylcellulose was demonstrated to represent a new type of particulate polymeric emulsifier.