Hair Breakage 280 Nonetheless, in short, the extreme effect of relative humidity is again noted, and is dramatically illustrated in Figure 20 which shows Survival Probability plots for Caucasian hair under 0.010– 0.011 g/μm2 repeating stress at 60% and 90% RH. Results predict almost 100% survival after 3,000 cycles at 60% RH, but almost 0% survival at 90% RH. Summary The above results illustrate how single fiber fatigue experiments provide fundamental information to understand the contributions of different variables on the tendency for hair breakage. The work shown herein illustrates the sizable effects of grooming forces, fiber dimensions, hair type and condition, and also the environmental conditions. Indeed, it is possible to model the effects of these variables and consequently predict the likelihood for failure as conditions change. Nonetheless, data collection is slow and therefore this approach is not appropriate for screening experiments. Also, it is again noted that we do not know the magnitude of forces encountered by individual fibers during real life grooming. The next section describes how this basic knowledge, and the mathematical modeling approaches, lead to a complimentary approach that allows for faster screening of formulas and other experimental conditions. Part 2: Repeated Grooming Experiments Repeated grooming experiments are commonplace in the hair care industry, and are frequently used as a means of communicating the benefits of conditioning products in preventing hair breakage (see Chapter 15) however, until relatively recently,8-12 they received little attention in the scientific literature. As the name suggests, testing simply involves repeated brushing or combing of hair tresses for a given duration, followed by counting the number of broken fibers that result. The work described above illustrates why conditioner products give rise to the substantial benefits during this testing. Namely, a lowering of the grooming stresses produces an exponential increase in the number of cycles-to-fail.
Previous Page Next Page