J. Soc. Cosmet. Chem., 23, 617-636 (September 14, 1972) Scanning Electron Microscopy and Other New Approaches to Hair Spray Evaluation RANDALL P. AYER, Ph.D., and JAMES A. THOMPSON, Ph.D. s Presented April 5, 1972, be[ore the New York Chapter Synopsis--The SCANNING ELECTRON MICRO•'COPE and its utility for studying HAIR SPRAY k-ILMS are described. The scanning electron microscope is an invaluable tool for studying the COATABILITY of hair spray films on individual or small groups of hair libors. Coatability can be improved by addition of certain SURFACTANTS to hair spray formulations and can be correlated qualitatively to hair spray properties such as luster, ap- I•earance, and flaking. Coatability does not correlate well with curl retention, another important property of hair sprays, which is much more dependent on the physical properties of the resin. Previ- ous methods for evaluating curl retention were inadequate therefore, a STATISTICAL APPROACH was developed. The method described is reliable, conclusions can be validated with a high degree of confidence and with these benefits, formulations can be optimized. INTRODUCTION Hair sprays have exhibited a remarkable growth over the 22 years they have been marketed. During 1971, the 500 million units sold represented about 20•o of the entire aerosol market. Part of the reason for the continued acceptance of hair sprays has been overall product improvement made possible through development of new resins. Another important factor has been selection of plasticizers and other additives to complement the resin's performance and appearance on women's, and more recently on men's, hair. "Freon" Products Laboratory, E. I. du Pont de Nemours 8c Co., '•Vilmington, Del. 19898. 617

618 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Root (1) and Shansky (2) both have described the historical develop- ment of resins used in hair sprays. A number of people have described various methods for evaluating the many different properties which affect a hair spray's performance and appearance (3-8). Of all the prop- erties (curl retention, luster, flaking, moisture permeability, tackiness, drying time, film hardness, coatability, combability, shampooability, dry- hess, build-up, feel), holding power or curl retention, along with those factors affecting it, has been the most extensively studied. The results of a series of Freon©* Products Division's consumer surveys on hair sprays also indicated the importance to the consumer of curl retention at high humidity without sacrificing natural appearance, feel, or manage- ability. The development of hair sprays having superior curl retention at high humidity, while maintaining other desirable qualities, was first ap- proached by studying the coatability and leveling of various hair spray films on individual or small groups ot5 hair fibers with a scanning electron microscope. The use of this instrument is described. The improve- ment of coatability and other properties by addition of certain surfac- tatits to hair spray formulations is discussed. Several techniques for measuring and evaluating curl retention have been described (4, 7, 9). These and methods previously used by us were inadequate for meaningful quantitative comparisons. A reliable, sta- tistical approach was developed to permit formulation optimization. The method is described and discussed. EXPERIMENTAL Apparatus and Methods The Scanning Electron Microscope The scanning electron microscope (SEM) has been commercially available since 1965. A number of articles have been written describ- ing the instruments on the market and their many applications including those in toiletries research (10-13). A brief description of the scanning electron microscope and its relationship to optical and transmission elec- tron microscopes (TEM) will be helpful for understanding the use and the advantages of the instrument for studying coatability of hair spray films. * Registered trademark of E. I. du Pont de Nemours & Co., Wilmington, Del. 19898.