Observations on the Cutting of Beard Hair

Donald E. Deem; Martin M. Rieger

CUTTING OF BEARD HAIR 589 (•) -- Fiber 1 (•) - Fiber 2 10 0 20 25 30 35 40 45 50 55 60 65 70 Temperature o C Figure 7. Temperature (oC) vs. force to cut (g) on same fiber (wet) Si•nilar studies of wet beard hair were conducted by measuring the cut- ting force of thoroughly hydrated fibers which ,vere maintained at the de- sired temperature by playing a stream of warm water on the fiber positioned in the jig. Two fibers were each cut about 10 times at each of 4 or 5 tem- peratures, and the results are shown in Fig. 7. The computed least square slope indicates that the f-t-c is lowered by 0.051 g/øC. These data demon- strate that shaving should be easier at elevated temperatures.

590 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS • 7 x ß x-x j-j 40øC o - o 55•C x ß ! ß x o o 1 2 3 4 5 Time (Minutes) Figure 8. Force to cut as a function of time of hydration of beard hair in dilute (0.5 per cent) sodium ]auryl sulfate at different temperattires In a third study the influence of temperature on beard hair hydration time was determined in the presence of a wetting agent (0.5 per cent sodium lauryl sulfate). In view of the number of cuts required, it was necessary to use dif- ferent hairs at different temperatures the fibers were selected to exhibit the same dry cutting force at room temperature. Nevertheless, one anomaly oc- curred in the data at 30øC. All the data are summarized in Fig. 8. It is ap- parent that the time required for full hydration is shortened by increasing

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CUTTING OF BEARD HAIR 589 (•) -- Fiber 1 (•) - Fiber 2 10 0 20 25 30 35 40 45 50 55 60 65 70 Temperature o C Figure 7. Temperature (oC) vs. force to cut (g) on same fiber (wet) Si•nilar studies of wet beard hair were conducted by measuring the cut- ting force of thoroughly hydrated fibers which ,vere maintained at the de- sired temperature by playing a stream of warm water on the fiber positioned in the jig. Two fibers were each cut about 10 times at each of 4 or 5 tem- peratures, and the results are shown in Fig. 7. The computed least square slope indicates that the f-t-c is lowered by 0.051 g/øC. These data demon- strate that shaving should be easier at elevated temperatures.

590 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS • 7 x ß x-x j-j 40øC o - o 55•C x ß ! ß x o o 1 2 3 4 5 Time (Minutes) Figure 8. Force to cut as a function of time of hydration of beard hair in dilute (0.5 per cent) sodium ]auryl sulfate at different temperattires In a third study the influence of temperature on beard hair hydration time was determined in the presence of a wetting agent (0.5 per cent sodium lauryl sulfate). In view of the number of cuts required, it was necessary to use dif- ferent hairs at different temperatures the fibers were selected to exhibit the same dry cutting force at room temperature. Nevertheless, one anomaly oc- curred in the data at 30øC. All the data are summarized in Fig. 8. It is ap- parent that the time required for full hydration is shortened by increasing

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CUTTING OF BEARD HAIR o- o Before x - x After 587 12 11 10 ø x x x o x o x o o 0 1 2 3 4 5 10 Time (Minutes! Figure 6. Hydration time before and after washing with sodium ]aury] sulfate (0.5 per cent) at 23 ø C value * (2) a stream of water or of a test solution was directed at the fiber, and cutting forces were determined as rapidly as possible during the first 9. rain after this, cuts were made at 1 min intervals (3) after 10 mina series of 10 cuts were made as a measure of the equilibrium cutting force in the wet state. *Fig. 5 shows that the "dry" f-t-c is relatively insensitive to variations in the range of 10 to 60 per cent relative humidity.

588 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II Hydration Time and Cutting Force as a Function of pH pH 9.1 6.84 4.01 Buffer 0.01 M borax 0.05 M phosphate 0.05 M phthalate Hydration time (rain) ñ std dev. 2.60 ___ 0.47 2.13 ñ 0.26 2.16 ñ_ 1.21 Force to cut wet (g) 4- std dev. 4.01 ñ 0.40 3.91 ñ 0.39 4.31 4- 0.31 Ionic Strength of buffer 0.060 0.091 0.053 The results of a typical experiment are shown in Fig. 6. Fo.llowing the determination of the initial hydration curve at 23øC (Fig. 6, before), the fiber was washed in 0.5 per cent aqueous sodium lauryl sulfate solution, rinsed with distilled water, and dried for 48 h in a desiccator over P205 a sccond hvdration curve was then detcrmincd (Fig. 6, aftcr). The absence of any significant difference suggests that the rate of hydration is not altered bv the removal of surface lipids. Based on the f-t-c, beard hair fibers appear to have been completely hydrated by exposure to water at room temperature within about 2 to 3 min. The rate of hydrarich of beard hair and the f-t-c could be expected to be dependent on the pH of the aqueous medium. Accordingly, cutting measure- ments were made in various buffer solutions, and the results are summarized in Table II. Any differences between the hydration times or between the f-t-c are sta- tistically insignificant. The ionic strengths and chemical composition of the buffers are different, but the variations are not likely to affect the results. These rather unexpected data indicate that the pH has little or no effect on the f-t-c or on the rate of hydration of beard hair. Effect of Temperature on Cutting Force It is part of shaving folklore that the use of cold water during shaving leads to an uncomfortable shave. It seemed important, therefore, to measure the effect of water temperature on the cutting force. Three types of experi- ments were performed on wet fibers and on dry fibers. For measurements on dry fibers, the fixture used for cutting beard fibers was fitted with a heating tape and a surface thermocouple. A single hair was cut (dry) 10 times at each of 4 temperatures. The average cutting forces and the standard deviations are tabulated in the chart below and indicate that the f-t-c of dry fibers is lowered by raising the temperature. Temperature (o C) 23 56 65 75 f-t-c (g) ñ std dev. 17.6 ñ 1.5 14.5 4- 1.3 12.3 ñ 0.80 13.1 ñ 0.84 Significance (Values connected by underlining are significantly different) _

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CUTTING OF BEARD HAIR o- o Before x - x After 587 12 11 10 ø x x x o x o x o o 0 1 2 3 4 5 10 Time (Minutes! Figure 6. Hydration time before and after washing with sodium ]aury] sulfate (0.5 per cent) at 23 ø C value * (2) a stream of water or of a test solution was directed at the fiber, and cutting forces were determined as rapidly as possible during the first 9. rain after this, cuts were made at 1 min intervals (3) after 10 mina series of 10 cuts were made as a measure of the equilibrium cutting force in the wet state. *Fig. 5 shows that the "dry" f-t-c is relatively insensitive to variations in the range of 10 to 60 per cent relative humidity.

588 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II Hydration Time and Cutting Force as a Function of pH pH 9.1 6.84 4.01 Buffer 0.01 M borax 0.05 M phosphate 0.05 M phthalate Hydration time (rain) ñ std dev. 2.60 ___ 0.47 2.13 ñ 0.26 2.16 ñ_ 1.21 Force to cut wet (g) 4- std dev. 4.01 ñ 0.40 3.91 ñ 0.39 4.31 4- 0.31 Ionic Strength of buffer 0.060 0.091 0.053 The results of a typical experiment are shown in Fig. 6. Fo.llowing the determination of the initial hydration curve at 23øC (Fig. 6, before), the fiber was washed in 0.5 per cent aqueous sodium lauryl sulfate solution, rinsed with distilled water, and dried for 48 h in a desiccator over P205 a sccond hvdration curve was then detcrmincd (Fig. 6, aftcr). The absence of any significant difference suggests that the rate of hydration is not altered bv the removal of surface lipids. Based on the f-t-c, beard hair fibers appear to have been completely hydrated by exposure to water at room temperature within about 2 to 3 min. The rate of hydrarich of beard hair and the f-t-c could be expected to be dependent on the pH of the aqueous medium. Accordingly, cutting measure- ments were made in various buffer solutions, and the results are summarized in Table II. Any differences between the hydration times or between the f-t-c are sta- tistically insignificant. The ionic strengths and chemical composition of the buffers are different, but the variations are not likely to affect the results. These rather unexpected data indicate that the pH has little or no effect on the f-t-c or on the rate of hydration of beard hair. Effect of Temperature on Cutting Force It is part of shaving folklore that the use of cold water during shaving leads to an uncomfortable shave. It seemed important, therefore, to measure the effect of water temperature on the cutting force. Three types of experi- ments were performed on wet fibers and on dry fibers. For measurements on dry fibers, the fixture used for cutting beard fibers was fitted with a heating tape and a surface thermocouple. A single hair was cut (dry) 10 times at each of 4 temperatures. The average cutting forces and the standard deviations are tabulated in the chart below and indicate that the f-t-c of dry fibers is lowered by raising the temperature. Temperature (o C) 23 56 65 75 f-t-c (g) ñ std dev. 17.6 ñ 1.5 14.5 4- 1.3 12.3 ñ 0.80 13.1 ñ 0.84 Significance (Values connected by underlining are significantly different) _

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).

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