CUTTING OF BEARD HAIR 591 the temperature. Again (see Fig. 6), the f-t-c completely hydrated fibers de- creases as the temperature is raised. Effect of Chemical Treatments The results of the studies reported so far indicate that the rate of hydra- tion of beard hair is relatively fast and that softening-as measured by f-t-c- is not significantly altered by modest changes in pH or the presence of a wetting agent. In view of this, the effect of potassimn stearate solution, aero- sol shaving cream concentrates, and several finished commercial creams on the f-t-c hair was determined. None of these materials showed any reduction of the hydration time or of the f-t-c the fiber beyond that effected by water. Therefore, it was decided to utilize a few more drastic chemical treatments. Since 1-propanol/water mixtures are known to make hair easier to extend (6) a 45:55 (w/w) 1-propanol/water mixture was directed on the fiber during cutting. The data given in the chart below show that the difference betxveen the wet and dry cutting force (47 per cent lowering) is about the same as that of samples treated with distilled water (51 per cent lowering). The hydration time is comparable to that of water-treated fibers. Dry Wet (propanol/water) Average f-t-c (g) ___ std dev. 6.20 ñ 1.40 3.27 ___ 0.82 Hydration times (rain) __+ std dev. -- 2.76 q- 1.44 In a more drastic procedure, beard fibers of known wet f-t-c were soaked in a commercial waving lotion (6.0 per cent thioglycolic acid, pH 9.3) for 5, 7, and 10 min, rinsed in several changes of distilled water, and then cut under a stream of water. The results tabulated in the chart below confirm again that significant chemical attack (7 min in wavir•g lotion) on the fiber causes only a rain.or (13 per cent) reduction in the cutting force (98 per cent confidence level). Fibers exposed to the waving lotion for 10 min could not be cut because of excessive damage to the fiber, which allowed it to bend and to be split axially. Time of Waving Lotion Treatment f-be q- Std Dev. (in g) Control Treated 5 rain 3.95 ___ 1.06 4.20 ___ 0.65 7 min 5.20 ___ 0.57 4.51 ___ 0.54 McLaren (7) has shown that wool is reduced more drastically in thiogly- colic acid in aqueous 1-propanol (45:55 w/w) than aqueous thioglycolate. Therefore, it was decided to measure the cutting force of fibers soaked (for 2 or 5 rain) in 1-propanol/water (45:55) containing either 0.5 per cent or

592 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 6.0 per cent thioglycolic acid adjusted to pH 9.2 with ammonia. In a separate set of experiments fibers were also treated with either 0.5 per cent or 6.0 per cent thioglycolic acid at pH 11.3 (with sodium hydroxide) for 9. or 5 min. Only exposure to 6 per cent thioglycolic acid at pH 11.3 for 5 min effected any lowering of the cutting force over that of water. The majority of the fibers with this treatment disintegrated before they could be cut, and the two fibers which could be cut bent during cutting. The conclusions, •vhich must be drawn from these studies, are that even the most severe chemical (covalent bond) damage, which is knoven to lower the tensile modulus drastically, has almost no effect on the force required to cut beard hair. In addition, rupture of hydrophobic bonds by 1-propanol/ water also appears to have almost no effect on the f-t-c. CONCLUSION A device is described which permits measurement of the force required to cut a beard hair fiber under a variety of conditions. Studies with this device show that the force required to cut wet beard fibers with commercial razor blades is about 65 per cent less than that of dry fibers. Beard hair is almost completely hydrated by exposure to water for about 2 min at room tempera- ture, and this hydration is accelerated by an in,crease in temperature. The force required to cut beard hair is not lowered below that of water by the presence of a wetting agent, shaving cream, or soap solution. The force required to cut wet beard hair with a razor blade is lowered significantly by verv severe chemical attack on the fiber. On the other hand, the force re- quired to cut beard hair increases as the rate of blade travel increases. ( Received December 3, 1975 ) I•EFERENCES (1) L. Hollander and E. 1. Casselman, Factors involved in satisfactory shaving, ]. Amer. Med. Assoc., 109, 95-101 (1937). (2) A. Dupr6, Cinqui6me M6moire sur la Th6orie M•canique de la Chaleur, Travail et Force Moleculaires II, Ann. Chim. Phys., 7, 236-82 (1866). (3) N. I. Muskhelishoili, Some Basic Problems of Mathematical Theory of Elasticity (trans- lated from the Russian by J. R. M. Radok), P. Noordoff Ltd., Gronigen, Holland, 1953. (4) Mary G. Natrella, Experimental Statistics, U.S. Govt. Printing Office, N.B.S. Hand- book 91, 1963, P. 5-24. (5) T. W. Mitchell and M. Feu•helman, The Torsional Properties of Single Wool Fibers, Part I, Text. Res. J., 3,0, 662-7 (1960). (6) J. C. Atkinson et al., Action of Mixed Solvents on Wool, Nature, 184, 444 (1959). (7) J. A. MacLaren, The extent of reduction of wool protein by thiols, Aust. J. Chem., 15, 824-31 (1962).