Green chemistry method for hair strengthening and setting using visible light-mediated protein crosslinking

A clean and nontoxic one-step protein crosslinking reaction method induced by visible light was developed using eco-friendly chemicals, such as riboflavin phosphate (RFP), citric acid (CA), and polyols. In this study, oxygen radicals generated by blue light (BL)-irradiated RFP replace the conventional free thiol generatio step of the alkali condition. CA and polyol were used as crosslinkers and extenders, respectively, to enhance keratin crosslinking in hair. The new one-step crosslinking method was compared with the existing permanent hair waving treatment using thioglycolic acid (TGA). Compared to TGA treatment, the newly proposed crosslinking method induced minor damage to hair and keratin. In addition, the mechanical property changes were measured after crosslinking treatment on the hair. The tensile stress values and Young's moduli of the treated hair samples were approximately 1.3 and 2.2 times higher than untreated hair. The hair-setting effect was also confirmed by the changes in the radii of the hair fibers and the length of the hair tresses after crosslinking treatment. Therefore, we believe that the clean one-step crosslinking technology can be used to develop eco-friendly products for hair strengthening and setting.