.I. Soc. Cosmetic Chemists, 18, 591-598 (Sept. 1(5, 1967) Effect of Process Variables on the Stability of Some Specific Emulsions H. E. JASS, Ph.D.* Presented before the New York Chapter, January, 1966, New York City Synopsis--Three case histories of cosmctic emulsion problems involving rheological and emulsion deterioration with time are described. Despite considerable variation in emulsion type, the three demonstrated similar changes which are traced to changes in the physical state of the crystalline viscosity builders, primarily glyceryl monostearate. It is shown how changes in processing and formulation were able to arrest these changes and stabilize the product. The role of photomicrography in helping to analyze the problem and in predicting the results of experiments is demonstrated. INTRODUCTION The literature on emulsion theory, technology, and stability pre- diction is probably the most extensive portion of the cosmetic chemist's library. Yet, no other problem facing the chemist today poses as much mystery or demands an empirical approach as does emulsion formula- tion. Admittedly, the contributions of the many researchers in this area have been extremely valuable. They have advanced knowledge in this area to a considerable degree, affording the formulator a greatly superior springboard for his leap into the unknown. However, despite their noteworthy efforts, a cosmetic chemist, even after careful scientific preparation, still must adopt an optimistic attitude and must devote considerable time to testing to confirm his product's stability. Despite the large background of intuitive knowledge possessed by experienced and skilled chemists, publication has been scanty, to * Carter Products Div., Carter-Wallace, Inc., Cranbury, N.J. 08512. 591

592 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the disadvantage of all. Despite the reluctance of scientists to publish data of unplanned and unorganized observations, this is a field in which such pragmatic information on usually complex systems can be valu- able, especially in supplementing basic research on simple emulsions such as exemplified by the recent paper by Sherman (1). As an ex- ample of such information, this paper presents a trio of case histories out of the daily effort under the pressure caused by the usual urgency of the cosmetic marketing situation. CASE HISTORIES Many varieties of emulsions have two types of emulsifier systems working in conjunction: the primary system, either anionic, cationic, or nonionic, which serves to emulsify by interfacial action, and a second- ary system, consisting of agents which act as stabilizers due to viscosity building or gelling action on one or more components of the emulsion system. Among the latter are such crystalline materials as glyceryl monostearate, cetyl alcohol, and beeswax, this last one being a combina- tion of both an anionic primary emulsifier and a gelling agent. It is with the use of these materials, whose value has made them generally used but whose crystalline properties pose special stability problems, that this discussion is concerned. All photomicrographs included in this paper are Polaroid photo- graphs taken from 35 mm Agfachrome color slides. The latter were made on a Zeiss Universal Microscope using polarized light at a 165X magnification. Where a scale is shown on the picture, each division corresponds to 6.5 •. Water-in-Oil Cream The first case concerns a water-in-oil cream emulsion, utilizing a beeswax-borax emulsifier system. Despite a good gross stability record in the laboratory, the pilot-plant-processed product demonstrated an alarming tendency to develop a grainy texture after a few months of storage, which was quite variable in its extent from batch to batch. The product was processed in the plant in the usual manner, the final emul- sion being milled in an Eppenbach Colloid Mill* at a narrow setting after cooling to slightly above room temperature and then further cooled to room temperature. Figure 1 is a photomicrograph of the finished cream when just a few days old. The occasional large agglomerates and a wide range of ir- * Gifford-Wood Co., Hudson, N.Y. 12534.