Internal structural changes in keratin fibres resulting from combined hair waving and stress relaxation treatments: a Raman spectroscopic investigation

ObjectiveThe objective of our research was to investigate the influence of chemical treatments (reduction, stress relaxation and oxidation) on hair keratin fibres. MethodsThe structure of cross-sections at various depths of virgin white human hair resulting from permanent waving treatments with stress relaxation process was directly analysed at a molecular level using Raman spectroscopy. In particular, the three disulphide (-SS-) conformations in human hair were compared by S-S band analysis. ResultsThe gauche-gauche-gauche (GGG) and gauche-gauche-trans (GGT) contents of -SS- groups remarkably decreased, while the trans-gauche-trans (TGT) content was not changed by performing the reduction process with thioglycolic acid. In addition, the high-temperature stress relaxation process after reduction accelerated the disconnection of -SS- (GGG and GGT) groups in the human hair, while the low-temperature stress relaxation process after reduction accelerated the reconnection of -SS- (GGG and GGT) groups. Moreover, the S-O band intensity at 1042 cm(-1), assigned to cysteic acid, existing in the cuticle region and the surface of the cortex region increased, while the GGG content significantly decreased by performing the oxidation process after the reduction and the high-temperature stress relaxation processes. ConclusionThe author concluded that the high-temperature relaxation process after reduction accelerated the disconnection of -SS- (GGG and GGT) groups, thereby leading to the remarkable local molecular disorganization (an increase in the cysteic acid content and a decrease in the GGG content) on the cuticle and cortex cells during the oxidation process. Resume ObjectifL'objectif de notre recherche etait d'etudier l'influence des traitements chimiques (reduction, la relaxation des contraintes, et l'oxydation) sur les fibres de keratine des cheveux. MethodesLa structure des sections a differentes profondeurs de cheveux blancs vierges resultant des traitements pour permanentes avec processus de relaxation des contraintes a ete analysee directement au niveau moleculaire en utilisant la spectroscopie Raman. En particulier, les trois conformations disulfure (-SS-) dans les cheveux humains ont ete comparees par une analyse de la bande S-S. ResultatsLa teneur en gauche-gauche-gauche (GGG) et gauche-gauche-trans (GGT) des groupes -SS- a remarquablement diminue, tandis que la teneur en (TGT) trans-gauche-trans n'a pas ete modifie par l'execution du processus de reduction avec l'acide thioglycolique. En outre, le processus de relaxation des contraintes a haute temperature apres un traitement reducteur accelere la deconnexion des groupe -SS- (GGG et GGT) dans le cheveu humain, tandis que le processus de relaxation des contraintes a basse temperature apres la reduction accelere la reconnexion des groupes -SS- (GGG et GGT). En outre, l'intensite de la bande S-O a 1042 cm-1, attribue a l'acide cysteique, existant dans la region de la cuticule et la surface de la region du cortex augmente, tandis que la teneur GGG diminue significativement quand on effectue le processus d'oxydation apres la reduction et le processus de relaxation de contrainte a haut temperature. ConclusionL'auteur conclut que le processus de relaxation a haute temperature apres la reduction accelere la deconnexion des groupes de -SS- (GGG et GGT), ce qui conduit a la desorganisation moleculaire locale remarquable (une augmentation de la teneur en acide cysteique et une diminution du taux de GGG) dans les cellules des cuticules et le cortex au cours du processus d'oxydation.