Chapter 6 217 IV were the strongest, and the weaker types were found in types VI through VIII (Figure 12). As with ethnicity, the geometric parameters are also influenced by the curl in hair. Curl type V was the thickest and when the degree of curl deviated away from that type by becoming looser or curlier, the cross-sectional values decreased (Figure 13). On the other hand, ellipticity showed a direct correlation with curl where the fibers were more elliptical as the degree in curl increased (Figure 14). These studies, and more, show that hair characteristics change according to degree of curl and ethnicity. However, since some ethnic groups have curlier hair compared to others, it is difficult to assess whether the results are related to ethnicity, curl or both. Table 4 shows the sampling distribution for hair types V, VI and VII where there were larger numbers of hair samples that represented each ethnic group. After analysis using two-way ANOVA, results reveal that both ethnicity and curl degree are drivers for all three assessed variables of break stress, cross-sectional area and ellipticity, as shown in Table 5. Table 5 Two-way ANOVA p-values. Data results are from 293 subjects and 14,650 tested fibers. *Values are significant when p 0.05. Property Ethnicity Curl Classification Cross-sectional Area ([mu]m2) 0.001** 0.003* Ellipticity 0.025* 0.005* Break Stress (MPa) 0.001* 0.001** The influence of geometry can easily explain why the mechanical properties in hair differ. It is thought the geometrical twists and kinks that are more prevalent in curlier hair can be local points of weakness that act as stress concentrators and result in higher fragility. However, when hair from different global regions that have the same curl are compared, the impact of geometry is significantly reduced and other possible factors for the observed differences must be considered. Thus, more work is needed to understand the
Previous Page Next Page