An investigation into physical and chemical properties of semi-solid self-emulsifying systems for hard gelatin capsules

Semi-solid systems for hard gelatin capsules, based on polyethyleneglycol 400/non-ionic surfactants/corn oil mixtures, have been examined as an eventual alternative to the classical liquid self-emulsifying systems. A combination of 15% of polyoxyethylene (20) cetyl ether and 15% of polyoxyl (60) hydrogenated castor oil was used as surfactant. The PEG 400/corn oil ratio has been modified and the ability of both surfactants to promote the emulsification of corn oil, at 37 degrees C and under conditions of gentle agitation, has been investigated by a conductimetric method. The water was added at constant flow rate and during emulsification the conductance of the dispersion was monitored continuously which enabled the processes of emulsification to be compared. Fine emulsions were obtained from quaternary systems containing 10-45% of corn oil added to the detriment of PEG 400. When a greater quantity of PEG 400 was substituted by corn oil the efficiency of the surfactants decreased considerably, and very coarse emulsions were obtained. The behaviour of the encapsulated formulations when placed in contact with water at 37 degrees C was in agreement with these observations. The self-emulsifying deficiency observed for these most lipophilic systems has been attributed firstly to the unfavourable PEG 400/corn oil ratio and secondly to an initial restriction in the performance of the surfactants.