198 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS is the key odor component responsible for the foot-like smell. Key odor compounds for axillary odor remain yet to be investigated, although short-chain fatty acids of compara- tively long carbon chain (C6-C10) seemed to comprise a fair portion of its "bouquet." After having clarified the chemical constituents responsible for the malodors, we aimed for a novel concept in eliminating offensive body odors, namely to "quench" body odor, rather than to "prevent" its generation with conventional antiperspirants and de- odorants. The latter conventional deodorizers have little effect in eliminating body odor once formed. The method of choice with which to efficiently "quench" short-chain fatty acids was to convert them into their corresponding metallic salts, and this was best accomplished by zinc oxide (3,4,6). Despite its outstanding ability to quench the odor of pungent short-chain fatty acids, zinc oxide possesses two shortcomings when formu- lated it into various forms of deodorant products: the clogging of aerosols and a rough texture. This is due to the undesirable aggregation of zinc oxide. Here again the con- cept of a hybrid powder was useful. By forming a hybrid powder of zinc oxide and spherical nylon powder, these shortcomings were overcome without sacrificing any of zinc oxide's deodorizing power (3,4,6). In the current study we prepared a hybrid powder of zinc oxide and spherical polyeth- ylene powder, and likewise of aluminum chlorohydrate and polyethylene powder. The texture of each individual powder and its corresponding hybrid powder was compared. The efficacy of hybrid powders in quenching isovaleric acid and caproic acid was also investigated by headspace gas chromatography. EXPERIMENTAL FORMATION OF HYBRID POWDERS In our previous studies (1-4,6), spherical Nylon 12 powder was employed as the core powder because of its excellent texture and our long experience in using it as a cosmetic raw material. In this study we have chosen another excellent organic powder, spherical polyethylene powder, which is not only cheaper but also disperses much better than nylon in LPG propellants. This is especially advantageous, since the use of chlorofluoro- carbons in aerosol products has been banned. Attempts were made to produce two different hybrid powders--both with spherical polyethylene as the core powder, the surface of which is coated with either zinc oxide (HPZ) or aluminum chlorohydrate (HPA). Spherical polyethylene powder (FLOWBEADS CL-2080, Sumitomo Seika Chemicals Co., Ltd.), of molecular weight 19,000- 20,000 and average particle size 15 p•m, was employed as the core powder. A micrograph (scanning electron microscope S-510, Hi- tachi Ltd.) of this powder is shown in Figure 1. The smoothness of the surface is readily observed. Fine-particle zinc oxide (99.7% as ZnO, average particle size 0.2 p•m) for preparing HPZ was obtained from Sakai Chemical Industry Co., Ltd. Figure 2 clearly indicates that despite its claimed average particle size, zinc oxide aggregates to form a massive lump. Fine-particle aluminum chlorohydrate of maximum particle size 5 p•m was obtained by

HYBRID POWDERS FOR BODY MALODORS 199 Figure I. Scanning electron micrograph of spherical polyethylene powder. pulverizing aluminum chlorohydrate (Hoechst, maximum particle size 50 gm) by means of a jet mill (single-track jet mill STJ-200, Seishin Enterprise Co., Ltd). A microscopic profile of fine-particle aluminum chlorohydrate is shown in Figure 3. Fine-particle zinc oxide and spherical polyethylene powder were added and mixed in various weight ratios inside a Henschel mixer (Mitsui Miike Machinery Co., Ltd., Model 10B) for five minutes. The mixture was placed inside a centrifugal ball mill (Retsch, Type S2) charged with alumina balls where it was mixed and compressed ii 0840 !$K !Suu Figure 2. Scanning electron micrograph of fine-particle zinc oxide.