26 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I Angle of Rotation (Degrees) About the Fiber Axis Under the Action of a Tensile Load (65% RH, 21øC) Weight (Specimen Lengths 65-95 RR) Added (g) • I 5 10 20 30 40 50 60 70 80 SpeciRen 1 2 3 --16 --30 --30 --21 30 92 120 88 brk. 20 - 7 --18 -18 -45 -41 5 -70 -187 7 -15 -33 -53 -70 -77 103 165 brk. brk. hair (e -- 1 to 1.4). The high ellipticity is a reflection of the flattened collapsed appearance which seems to be a typical characteristic of Negroid hair. The influence of increasing load on torsional untwisting of fiber specimens 65 to 95 mm in length is shown in Table I. The angles of rotation change in sign during the course of a single measurement, suggesting the presence of at least two twists in the specimen in opposite directions. Indeed, the twisted configuration shown in Figure 3 does not appear to be helical or unidirectional over an extended length of the fibers. Table II Angles of Axial Rotation (Degrees) of Negroid Hair Under Tensile Loading (65% RH, 21øC) (Specimen lengths 1-2 RR) Weight (g)• 5 10 20 30 40 50 60 70 80 90 100 110 SpeciRen 1 2 3 4 5 6 7 8 9 lO 11 12 13 14 15 16 17 18 19 0 --11 --16 --20 --29 --33 --40 --46 0 --7 --24 --47 --81 --174 brk. 0 0 -8 -17 -29 -51 -41 brk. 0 3 13 16 26 42 42 42 0 -9 -15 -43 -61 -109 -117 -136 0 -5 -12 -21 -21 -2 11 11 0 -4 -17 -51 -47 brk. 0 --4 --6 --10 8 58 a (brk.) 0 6 23 45 97 69 69 brk. 0 -6 -19 -27 -65 -94 -107 -115 0 4 12 24 25 33 33 36 0 -24 -62 -128 -177 -207 -193 saved 0 -118 -147 -147 -164 -143 saved 0 4 19 9 29 50 57 66 0 0 18 7 -5 brk. 0 --4 --9 --87 --70 --70 saved 0 19 30 42 73 85 90 0 4 10 13 31 17 25 0 4 4 4 14 14 11 20 0 0 8 19 36 60 brk. 21 0 2 4 8 16 40 53 -34 brk. 59 57 brk. -133 -133 brk. brk. brk. 33 33 -43 57 57 brk. 192 216 brk. saved 11 li b (brk.) 42 saved brk. aBroke during weight change. bBroke during the angle measurements.

BEHAVIOR OF NEGROID HAIR 27 Therefore, these measurements were repeated on much shorter fiber specimens (1-2 mm) with a single region of twist. Angles of rotation for these shorter specimens are shown in 'Fable II. The position of the crossbar with a weight of 5 g was considered as the initial position (0ø), and the changes in angle with subsequent loading were measured with reference to this position. Angles of rotation in Table II usually increase in a given direction with load until the breaking point is reached. This indirectly confirms that the results in Table I were due to the presence of multiple twist reversals in the specimen. On some fibers, however, the angle of rotation decreases prior to break (specimens 1, 6, 8, 9, and others). It is suggested that this decrease is due to the initiation of cracks which relieve the torsional stress on the specimen, and that the growth of these cracks subsequently leads to fracture. In order to check this hypothesis, some fibers were saved as soon as the decrease in rotation angle was observed and examined in the scanning electron microscope. In a few of these fibers, cracks were indeed observed (Figure 5). It should Figure 5. Generation of a crack in the region of twist in torsional untwisting under the influence of a tensile load. a) 200x. b) 800x. c) 2400x. be noted, however, that this does not provide definitive evidence that they were formed during the stretching of the fiber, since occasional cracks or flaws have been found before stretching.