Since African descent hair is extremely curly, it is very difficult to comb. The two studies have been reported with respect to the comparison of combing forces required to comb African descent hair and Caucasian hair in both wet and dry states (Epps, et al., 1983[i] and Syed et al[ii]. It is reported that wet African hair is 4 to 5 times more difficult to comb than wet Caucasian hair, as shown in Figure 2.17.
Figure 2.17: The comparison of force required to wet comb Caucasian and African-descent hair
Similarly, dry African hair is almost 53 times more difficult to comb than dry Caucasian hair, as shown in Figure 2.17
Figure 2.18: The comparison of forces required to dry comb Caucasian and African-descent hair
African descent dry hair is 8 times more difficult to comb than wet African descent hair.
Repeated Hair Combing and Brushing – An Indication of Hair Breakage:
When hair fibers are repeatedly combed or brushed, they tend lose their strength and become weaker along with chipping away some of the cuticles. The hair fibers, when combed 200 times repeatedly lose up to 4.0% of the their elasticity. It is an arduous job to comb hair repeatedly, therefore, hair combing or brushing machines are devised for laboratory use. The example of a one simple combing/brushing machine is shown in Figure 2.19.
Figure 2.19: The combing/brushing machine for an automatic combing/brushing for a known number of strokes
When untreated Caucasian hair fibers that are 4 g in weight and 5 inches in length, are brushed using 3600 strokes, close to 716 fibers break during this brushing exercise. When similar weight and length tress is treated with a conventional relaxer and brushed for 3600 times, the number of broken fibers exceed significantly.
Tensile properties of Hair
The break stress of untreated wet African hair is 0.089 ± 0.025 10x9 N/m² as compared to a break stress of 0.165 ± 0.025 10x9 N/m² for wet Caucasian hair. Similarly, the break stress of untreated dry African hair is 0.153 ± 0.015 10x9 N/m²as compare to a break stress of 0.189 ± 0.019 10x9 N/m² for untreated dry Caucasian hair[iii].
[i] J Epps, and LJ Wolfram. (1983). Letter to Editor. J Soc Cosmet Chem, vol. 34, pp. 213-214.
[ii] AN Syed, et al. (1995). African-American Hair: Its physical properties and differences relative to Caucasian hair. Cosmetics & Toiletries Magazine, vol. 110, p. 45.
[iii] Ibid, p. 43.