44 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II Angle of Torsional Rotation (deg) of Negroid Hair Under Tensile Loading (65% RH, 21øC) Weight (g) 5 10 20 30 40 50 60 70 80 Specimen 2 0 -7 --24 -47 -81 - 174 Brk 6 0 -5 -- 12 -21 -21 -2 11 11 9 0 6 23 45 97 69 69 Brk Brk Note: Sign of the angle refers to right or left handed rotation. already having a crack which grows catastrophically, leading to fracture. The second type of behavior is probably characteristic of fibers which do not have a crack. The reduction in the torsional angle suggests that a crack is generated in the fiber at that load level, leading to some degree of stress relaxation prior to fracture. ROLE OF TENSILE-TORSIONAL FATIGUE IN THE GROOMING OF NEGROID HAIR Combing or stretching of Negroid hair can be considered as involving tensile and torsional fatiguing of fibers in the regions of twist. To study the possible long-range effects of combing and stretching, an accelerated tensile fatigue test was developed the details of the apparatus and experimental procedure were given earlier (2). Fibers were subjected to various load levels for a maximum of 11,000 cycles. A failure distribution was obtained by noting the cycles to failure for each specimen. Specimens surviving 11,000 cycles were subjected to tensile fracture on an Instron machine to determine whether the mechanical properties reflect the effect of fatiguing on the structure of the Table III Lifetime Distributions of Untreated, Superrelaxed (SR), and Thioglycolate-Treated Negroid Hair Fibers Percent of these failures occurring in different frequency ranges Load Failures (g) Treatment (%) Imm. (0 kc) 0-0.5 kc* 2-11 kc Untreated 14 12 18 42 10 SR 20 16 58 14 TGA 11 18 46 18 Untreated 15 25 37 38 20 SR 12 18 54 34 TGA 17 9 31 62 Untreated 31 17 50 30 30 SR 39 29 60 32 TGA 42 32 56 29 Untreated 54 29 53 20 40 SR 79 48 67 16 TGA 82 60 82 7 Includes immediate failures.

EFFECTS OF TREATMENTS ON NEGROID HAIR 45 Table IV Fracture Pattern Distribution of Negroid Hair Fibers Fatigued to 11 kc Under Various Loads (Survivors) (Fracture at 65% RH) Fracture type (%) Load Number of Brk. Fibers Below (g) Specimens Ext. (%) 22% Ext. (%) Smooth Step Angle Split Fibrillated Untreated 0 36 27 ñ 5 22 6 56 6 l0 32 10 74 32 ñ 3 •4 3 76 8 7 7 20 66 32 ñ 3 13 6 73 11 3 8 30 43 33 ñ 3 10 7 81 9 0 2 40 29 30 ñ 4 17 7 79 7 7 0 SR 0 50 39 ñ 5 16 40 32 4 8 16 10 62 46 ñ 4 10 48 34 3 6 8 20 69 41 ñ 3 8 62 30 1 4 1 30 42 40 ñ 4 7 38 55 2 2 2 40 11 34 ñ 8 9 9 91 0 0 0 TGA 0 50 41 ñ 6 24 40 34 6 10 10 10 67 43 ñ 5 19 64 25 1 6 3 20 57 44 ñ 4 12 67 26 4 4 0 30 33 39 ñ 5 12 73 21 6 0 0 40 12 40 ñ 8 8 42 58 0 0 0 fiber. The nature of the fracture ends was examined either by optical or scanning electron microscopy. Negroid hair fibers after different treatments were subjected to this fatiguing process to understand the factors that lead to fracture and the particular fracture patterns. Lifetime distributions of Negroid hair with different treatments are shown in Table III. Most specimens seem to fall in the 0-0.5 kc and 2-11 kc range a few fibers falling between these ranges were neglected. The data in Table III show that super- relaxed (SR) and thioglycolate (TGA)-treated fibers break in larger numbers in the 0- 0.5 kc range with increase in load. Even the number of immediate failures increases with an increase in load as compared to the untreated fibers, suggesting that these chemical treatments have a deleterious effect. Immediate failure may be due to preex- isting damage accentuated by chemical treatments. As would be expected, the number of specimens breaking in the 0-0.5 kc range increases and the number in the 2-11 kc range decreases with increase in load levels. FRACTURE PATTERN DISTRIBUTIONS The five types of fracture pattern observed as a result of tensile deformation of Negroid hair have been discussed elsewhere (2). Fracture pattern distributions of fibers surviving the fatigue test (11 kc) and broken on the Instron machine in the tensile mode are shown in Table IV. Untreated fibers show high percentages of step fractures. A con- siderable increase in smooth fractures is observed with superrelaxed and thioglycolate- treated fibers, with a consequent decrease in the percentage of step fractures. The