Prediction of bending set, wave efficacy, and hair damage using an extensional permanent waving treatment and the 20%...

To predict "wave efficacy" as evaluated by hairdressers, an extensional permanent waving treatment was performed on human hair fibers using various wave lotions manufactured in Japan. Glass columns devised for the purpose were equipped with a tensile tester in order to increase the measurement accuracy. Notably, the observed set agreed with the theoretical set. In addition, the data for the extensional set exhibited good correlation with the bending set and the wave efficacy assessed in a beauty parlor, and hair damage was estimated by the characteristic change in the 20% index. The following facts were experimentally determined. First, the Young's modulus of the hair fibers after extensional permanent waving treatment continually decreased with an increase in the reduction of the fibers and then abruptly decreased at 80% reduction. Second, the reduction of hair treated with the ammonium salt of thioglycolic acid followed pseudo first-order kinetics only during the initial stage of the reaction, independent of the pH level. Third, the 20% index of the individual virgin hairs remained constant in water at 30°C and also correlated with the Young's modulus of the hair after extensional permanent waving treatment.