INTERACTION OF SURFACTANTS AND KERATINS 59 • 70 • 6o ¸ ! • 50 i 40 3o 2o 10 Figure 20. % unbeh o-o NQ- HexadecyLsuLfate, ck o •.o•oJ'dod•ecethepol.vg-alcohol •X HexQdecy[trimethy[- gmmoniumbrorr,)•de (X•x •, x__ x 0 10 10 • 10 10 • Surfactant Concentration i MoLe / [! The urea-bisulfite solubility of wool, exposed to pH 9 solution at 60øC for 2 hr as a function of surfactant concentrations in solution. Abscissa: surfactant concentration coordinate: urea bisu|fite solubility. (Reproduced with permission from reference 18.) processes have been studied extensively during the last few years (16). For instance, Meichelbeck and Knittel (17) determined the urea bisulfite solubility of wool samples after they had been exposed to surfactant solutions of increasing concentrations at various pH values. Under alkaline conditions, where the attacking species were the

60 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 260- 240- 220- 200 - 180- 160- 140- 120- 100 60- 4.O Figure 21. i \ \ / \ / \ / t 0.01 m Hexadecyttr•methy[- i ,• ammoniumbromide •/ without surfactant :•' 001 m cy[sutfc]t½Dode-•Nc]- 3 4. 5 6 ? 8 9 10 • pH Cystein S-Suffonic acid production in ,vool in the presence of surfactants. Treatment conditions: exposure to 0.2M Na2SO• at 50øC for 1 hr. Abcissa: pH coordinate Cystein-S-Sulfonic acid content. (Reproduced with permission from reference 17.) hydroxyl ions, these authors found that the presence of anionic detergents protected the wool against chemical changes. The cationic detergents, under the same conditions, on the other hand, enhanced the damage to the fibers. Nonionic surfactants did not show any additional effect beyond the normal degradation of keratin which occurred when it was exposed to prolonged treatments of alkaline media (Figure 20). These results could be explained by assuming that the absorbed negatively charged surfactant molecules repulse the OH- ions and, similarly, that the presence of the positive detergents attracted these attacking species to the vicinity of the disulfide bonds. Exactly the opposite type of results were obtained when the effect of cationic and anionic surfactants were investigated under acid conditions. In those cases, the attacking species were the hydrogen ions and, consequently, the cationic detergents exerted the protecting effect on the keratin. Finally, let us consider the effect of detergents on the very important reductions which