PRACTICAL SELECTING METHOD OF WAVE LOTION FOR HAIR DRESSER 53 20% index value is 61.6% and a line L or R hysteresis curve is obtained, medium to hard damage (Ero 50%) can be expected. Summarizing the above, only the 20% index value can be used to estimate hair damage if virgin hair is to be treated, but it is insuffi cient for estimating the damage to hair that has previously been repeatedly permed. The relationship between the values for Ero and the 20% index for repeated permanent treatments must be further investigated. Mechanism of the abrupt decrease in Ero at Pa = 80%. We speculate that the steep decrease in the value of Ero can be interpreted by the two-phase concept (19) hair fi ber consists of continuous linear and elastic fi laments (phase C) embedded in an amorphous matrix (phase M). To substantiate whether the steep decrease in Ero is related to only phase C or both phases C and M, both values for Ero and the 20% index were obtained for various values of Pa using the same hair fi ber, because the large increase in the 20% index value at Pa = 80% might be related with the abrupt variation in the value of Ero. As can be seen in Figure 13, a steep increase in the 20% value coincided with a rapid decrease in the value of Ero at approximately Pa = 80%. These results indicate that the steep decrease in Ero is related not only to phase C but also to phase M, because a steep increase in the 20% index indicates initiation of entanglement of the fi laments in the microstructure of the hair. This entanglement of the fi laments in phase C and M occurs by disorganization of the microstructure of hair, then the fi laments in both phases are liberated from the originally restrictive structure loosened and entangled. Consequently, the locations of SH residues produced in the crystalline fi laments are no longer located near one another where they can be readily reoxidized using an aqueous Figure 11. Estimation of hair damage (Ero) using the 20% index. Plot of Ero vs. the 20% index values listed in Table VI (the number affi xed to each plot indicates the Exp. No. in Table VI). With increasing hair damage, the 20% index decreased up to Ero = 80% along line H and then increased along line L forming a V shape. Line R: results for four repeated permanent treatments. Note: The 20% index value for virgin hair was constant in water at 30 °C (See Table V).

JOURNAL OF COSMETIC SCIENCE 54 Figure 12. Changes in the hysteresis curves with an increase in hair damage. Hysteresis curves obtained for the 20% index values (A),(B),(C), and (D) were determined under the conditions listed in Table VI (Exp. Nos. 0, 3, 9, and 16). (A) Virgin hair, (B) a little damaged hair (on line H), (C) hard damaged hair (on line L), and (D) hard damaged hair by repeated treatments (on line R). Note: The curvatures indicated with arrows de- creased as the hair damage increased. 0.03g/100g H2O2 solution (21). The entanglement of the fi laments therefore prevents the reformation of the original closed paired SH residues between the crystalline fi la- ments and only a few closed SH residues remain that can, upon reoxidation, form S–S bonds between the crystalline fi laments. In initiation of disorganization, it is speculated that cleavage of the crosslinks that join phase C with phase M are reduced at this point, because they seemed to be the most resistant to reduction and correspond to approxi- mately 11.9% of the internal fi laments in phase M, as estimated by Naito and Arai. The overall result would be a steep decline in the value of the Young’s modulus at Pa = 80%. If this proposed mechanism is correct, then avoidance of the disorganization caused by the fi ssion of the crosslinks between phases C and M would be critical. A study of the