200 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 3. Scanning electron micrograph of fine-particle aluminum chlorohydrate (ACH). mechanochemically to produce HPZ. HPA was produced by treating fine-particle alu- minum chlorohydrate and spherical polyethylene powder in the same manner. TEXTURE EVALUATION OF HYBRID POWDERS The texture of fine-particle zinc oxide, HPZ, fine-particle aluminum chlorohydrate, and HPA was evaluated by directly applying the powders to human skin (direct evalua- tion method) and by measuring their coefficients of kinetic friction by instrumental means (instrumental evaluation method). Direct evaluation method. Double-blind trials for evaluating fine-particle zinc oxide and HPZ directly on human skin were performed. A panel of 20 subjects (8 men and 12 women) from our Research Center, who had not been specially trained for evaluating the compounds of interest, was chosen. Each subject was given two figured bottles, one containing fine-particle zinc oxide, and the other, HPZ. The identity of each bottle was only distinguishable by the supervisor who collected the final results. The subjects applied each powder ad libitum on the back of their hands, and by rubbing them were asked to compare the texture of the two powders as cited below: A B: A is by far preferred to B A B: A is preferred to B A = B: A is more or less equal to B A B: B is preferred to A A 4 B: B is by far preferred to A The same experiment was carried out on fine-particle aluminum chlorohydrate and HPA as well. Instrumental evaluation method. To measure the coefficients of kinetic friction, a friction analyzer (7) that we have developed to evaluate the texture of various powders was

HYBRID POWDERS FOR BODY MALODORS 201 utilized. This analyzer consists of a horizontally placed iron plate on top of which is affixed a double-sided plastic tape to mount the sample. After mounting the sample, an aluminum attachment is placed on top of the sample. After pressing the aluminum attachment at a load of 5-150 g/cm 2, the attachment was moved left and right at a speed of 10 mm/sec. The resulting grinding stress was measured using a strain gauge. A graph was plotted, taking the x axis and y axis as load and grinding stress. The slope of this graph corresponds to the coefficient of kinetic friction. EVALUATION OF HYBRID POWDERS AS QUENCHING ACTIVES Equilibrium headspace gas chromatography (HSGC) was chosen to evaluate various compounds' ability to quench short-chain fatty acid malodors. This methodology en- ables us to measure only volatile constituents without the interference of involatile matters that we are neither interested in nor would like to introduce into the gas chromatographic system. It is also in good resemblance with human olfactory detec- tion. Isovaleric acid (C5HloO2) and caproic acid (C6H1202) were chosen as the target compounds to be quenched, since, as mentioned before, the former is the key odor component of foot odor, and the latter has been identified in axillary odor. The compounds under study are zinc oxide, aluminum chlorohydrate, spherical poly- ethylene powder, talc (Talc 15, Asada Seifun Co., Ltd.), benzalkonium chloride (C22H4oCIN, 50% aqueous solution, Toho Kagaku Co., Ltd.), HPZ, and HPA. Ten milligrams of each sample was weighed accurately in a glass vial especially designed for the headspace gas chromatograph, to which 2 ml of standard aqueous solution con- taining 0.3% of both isovaleric acid (Wako Pure Chemical Industries, Ltd., )98%) and caproic acid (Sigma Chemical Company, )99%) was accurately added. The hybrid powders Were also sampled to contain 10 mg as zinc oxide or aluminum chlorohydrate. The vial was tightly closed and placed inside an ultrasonic generator for 10 minutes for sample dispersion. It was then placed inside a 70øC oven for 60 minutes to equilibrate the vial headspace with acid vapor. The vial was introduced into a Hewlett Packard Headspace Sampler HP-19395A, which was attached to the injection port of a Hewlett Packard HP-5890 gas chromatograph equipped with a flame ionization detector and an HP-20 M (10 m X 0.53 mm i.d., film thickness 1.33 Ixm) column. The gas chro- matograph was programmed from 100 to 160øC at a rate of 10øC/min, with helium (10 psi) as carrier gas. The headspace of the vial was automatically pressurized, and a por- tion of it was forced into the carrier gas flow. The GC profile was recorded, and the peak areas were calculated in arbitrary units by an HP-5895A GC workstation, which also controlled the whole headspace GC system. For each sample, three consecutive GC runs were acquired, and the mean peak area was employed for the calculation described afterward. The standard acid solution was measured once in every five sample runs to ensure the stability of the headspace GC system. Each powder was evaluated by a value expressed as the odor suppression rate (OSR). OSR is calculated by the formula shown below. A-B OSR (%) - x 100 A A refers to the peak area of acid in standard acid solution B refers to the peak area of