.T. Soc. Cosmetic Chemists, 19, 109-117 (Feb. 5, 1968) Studies of Glyceryl Monostearate* RAYMOND M. CORNISH, B.S.t Presented May 2, 1967, New York City Synopsis--The properties of commercial glyceryl monostearate have been investigated in order to understand more fully its long term behavior as a raw material and as an emulsion component. Emphasis has been on physical properties as studied by X-ray diffraction, differential thermal analysis, and optical microscopy. Several manifestations of slow changes in the crystalline state which are time- and temperature-dependent have been observed. Applica- tion of these results to a specific emulsion problem is discussed. INTRODUCTION The work described in this paper had its origin in a study which was done to determine the mechanism of breakdown of a dispersion formulation. That earlier work had established that the principal source of instability in this formulation was the glyceryl monostearate (GMS). The studies were extended in an effort to enlarge our under- standing of the properties of this component (GMS) and thus gain better control of formulations in which it is used. The usual quality control procedures were followed for monitoring GMS as it was used in production. These called for certain standards of iodine number, melting range, monoester content, etc. This grade of glyceryl monostearate was known to increase in acid value over a period of time and so a limit to storage time was adopted to keep this parameter at a low value. In spite of these checks, the use of GMS was not always predictable. * We wish to thank Carter Products, Division of Carter-Wallace, for the support and permission to publish this work. • Arthur D. Little, Inc., 15 Acorn Park, Cambridge, Mass. 02140. 109

110 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS This work, therefore, was initiated to investigate the applicability of some of the more modern instrumental techniques for determining dif- ferences among samples of GMS. As the work progressed over a period of several months it was interesting to note the interdependence and significance of a number of these analytical techniques. The work described herein includes the application of the techniques of X-ray diffraction, differential thermal analysis, and microscopy. These three techniques have demonstrated certain behavior patterns which appear to be related. The author's observations also suggest the mechanism by which GMS introduces an instability problem into every formulation in which the compound is used. Finally, it is believed that this work indicates areas of study which might broaden one's under- standing of the properties of these types of material and thus allow the use of GMS in cosmetic products with a great deal more confidence than it now enjoys. Although other analytical techniques such as in- frared spectrophotometry and chromatography (both TLC and GC) have been investigated, the three approaches described below have pro- vided the most useful information. X-RAY DIFFRACTION An initial basis for comparison is the crystal structure. The litera- ture contains several references on polymorphism in GMS, and in fact, the work done by Kuhrt, Broxholm, and Bloom (1) was in part sugges- tive to this approach. The initial diffraction patterns which were ob- tained approximated those reported by Kuhrt et al. although a strict comparison was not in order because they used a high purity, specially prepared, monoester. The studies reported here were concerned with a commercial grade and the practical application of polymorphism as ap- plied to a product. Kuhrt and co-workers reported certain types of diffraction patterns according to the way and manner in which a sample was heated and chilled. These are attributed to two basic polymorphs--an unstable alpha plus a stable beta form. Several sub forms are also described. As our data began to accumulate, it was noted that considerably dif- ferent patterns could be obtained for GMS, which were not necessarily the result of melting and chilling. TP.e diffraction data obtained suggest that GMS undergoes a slow, but continuous, change in its crystalline state. When freshly solidified from the melted or amorphous condition, the initial crystallization is characterized by a single strong diffraction line between 4.06 and 4.17