Synthesis and emulsification properties of polyglyceryl estolides prepared from fatty acids

Polyglyceryl polyricinoleate (PGPR) is an emulsifier produced by esterification of polyricinoleic acid and polyglycerol. Polyricinoleic acid is derived from ricinoleic acid, which is expensive compared to other fatty acids. Therefore, analogues of polyricinoleic acid should be made from less expensive fatty acids, such as oleic acid. Therefore, oleic acid was converted to polyhydroxy estolide (PE) by a reaction with hydrogen peroxide and acetic acid. The PE was used as a substitute for polyricinoleic acid to produce PGPR analogues by direct esterification with polyglycerol and various fatty acids. The direct reaction between polyglycerol and PE produced a polyglyceryl estolide (PGE) with high viscosity and hydroxyl value, which limited its suitability as an emulsifier for the isopropyl myristate (IPM) and water system. Conversely, PGE prepared from lauric acid, polyglycerol and PE showed lower viscosity and hydroxyl value, resulting in a broad region of emulsion stability on a phase diagram when evaluated as a water-in-oil emulsifier for the IPM/water system. Similarly, other PGE made with oleic acid also displayed good emulsion stability for systems with higher IPM concentrations. In contrast, PGE prepared with stearic acid was a semi-solid at room temperature. Most of the prepared PGEs showed promising potential as emulsifiers for water-in-oil emulsions.