Kuzuhara A - This study pursued a scrutiny of the reduction mechanism of thioglycerol (TG) on hair keratin fibres. The findings disclosed that the waved virgin human hair treated with TG adjusted to pH 9.0 with ammonia solution, appeared to be less damaged than the waved hair treated with thioglycolic acid (TGA), regardless of its good waving efficiency. This was attributed not only to the gauche-gauche-gauche (GGG) and gauche-gauche-trans (GGT) conformations being disconnected, but also to the variation in the TGT conformation through the reduction process with TG.

Methods

• A direct inspection was conducted of the structure of cross-sections at various depths of virgin white human hair resulting from the permanent waving process with TG, at the molecular level with the aid of Raman spectroscopy.
• The optical microscopy examined the penetration of TG for the cross-sectional samples dyed with methylene blue.

Results

• A significant decrease was reported in the gauche-gauche-gauche (GGG) and gauche-gauche-trans (GGT) conformations of disulfide (-SS-) groups.
• In contrast, the trans-gauche-trans (TGT) conformation increased by performing the reduction process with TG.
• The disconnected -SS- content at various depths of the hair sample reduced with TG adjusted to pH 9.0 with ammonia solution, increased than with that of the hair sample reduced with TG adjusted to pH 9.0 with monoethanolamine.
• A strong tensile strength of the waved hair treated with TG was disclosed while adjusting to pH 9.0 with ammonia solution, compared with that of the waved hair treated with thioglycolic acid (TGA).
• However, the waving efficiency of the waved hair treated with TG was found to be higher than that of the waved hair treated with TGA.