CATIONIC CONDITIONING COMPOUNDS 71 A = unextended B = random scale lifting C -- common scale lifting D = extreme scale lifting E = fiber failure a scale Lifting phenomenon i. I1 A = unextended B = random scale lifting C = common scale lifting D = extreme scale lifting E = fiber failure 70 60 50 40 30 20 scale Lifting Phenomenon lO i. I1 Figure 7. Distribution of random, common, and extreme scale lifting observed as a mechanism of stress release of the cuticula during extension of hair fibers exposed to (a) single and (b) multiple applications of PQ-10.

72 JOURNAL OF COSMETIC SCIENCE transient cross-linking by formation of salt linkages, thus improving both cuticular adhesion/cohesion and preventing, or reducing, failure at the scale edges and with it high levels of scale lifting. Hair fibers treated with a HPG derivative. In contrast to unaltered hair fibers treated with the PQ-10, hair fibers treated with one as well as ten applications of the HPG derivative display a rather similar scale-lifting behavior during extension (Figure 8a, b). After both single and multiple applications of this polymeric quat, there are some hair fibers that do not display any scale-lifting phenomenon at all and fail at rather high extension levels. However, after both single and multiple treatments, most hair fibers still show random scale lifting at varying levels of extension, while common scale lifting follows less frequently, and extreme scale lifting is observed in only 50% of the fibers that showed random scale lifting. The high extension level at which failure occurs in the polymer-treated hair fibers suggests a beneficial role of the polymers to the hair fiber. The mechanism of inhibition of scale lifting by this cationic polymer is similar to that suggested for PQ-10. However, the differences may be related to specific polymer characteristics, e.g., the degree of substitution of cationic sites, which can affect the amount of residues left in the fiber after rinsing. Hair fibers treated with CETAB. The extension behavior of hair fibers exposed to one and multiple applications of CETAB shows similar trends (Figure 9a, b). As a result of the treatment, the overall scale lifting has decreased, especially at the extreme levels of scale lifting. This becomes even more pronounced after multiple CETAB applications. After single and multiple CETAB applications, some hair fibers may not display the scale- lifting phenomena at all, but most of them fail at rather high levels of extension. Most hair fibers do show random scale lifting at greatly varying levels of extension, while common scale lifting follows less frequently, and extreme levels of scale lifting is sparse. Less than 30% of the fibers showed extreme scale lifting for the once-treated fibers, and the percentage decreases further for the ten-times-treated fibers. The various levels of scale lifting occur at high levels of extension and with considerable scatter, the latter especially for the ten-times-treated hair fibers. Hair fiber failure occurs at somewhat lower levels of extension, especially for hair fibers treated ten times. Once again, the mechanism of improving scale-lifting resistance by this low-molecular- weight cationic surfactant is similar to that suggested for the polymeric type (formation of salt links and hydrophobic bonds), except that in this case, the amount of cationic absorbed into the cuticular sheath as well as the cortex (because of low molecular weight) can be large. Introduction of large amounts of lipid moieties into the cortex may hypothetically reduce the moisture level, leading to lower extension at break, especially for ten-times-treated hair fibers. STATISTICAL EVALUATION The statistical significance of the treatment effects was evaluated by comparing the proportion of fibers showing different degrees of scale lifting (4). A statistic z was calculated according to the equation given below: