Caracterização de fios de cabelo antes e após tratamentos químicos e físicos por espectroscopias Raman e no infravermelho e microscopia eletrônica

Abstract

Several different chemical and/or physical treatments can promote modifications of the hair fiber, and frequently more than one procedure is done on the same hair, as a part of a sequence of beauty requirements. In the present work we focus on the analysis of white hair from two different ethnic groups, Caucasian and African, before and after the changes promoted by distinct treatments: thermal, discoloration and straightening. Besides observing the damages caused by each the treatments separate, we have investigated all of the three processes in the same hair sample from each ethnic group. The characterization of all samples was performed with Raman and infrared vibrational spectroscopic techniques, and scanning electron microscopy for the morphological analysis. The vibrational spectroscopic results clearly pointed a prominent difference between the natural Caucasian and natural African hair samples, mainly based on the intensity of the amide III mode; this band is more intense in the African hair sample, meaning that this kind of hair presents a more disordered structure when compared to Caucasian hair. After the treatments it was possible to observe that several important chemical bonds, such as S-S, C-S, C-C and S-O in the hair structures, as well secondary protein structures were altered in their conformations. The exaggerated heat action generated changes in intensity for several bands in the Raman and infrared spectra when compared to the other treatments, whereas the action of all the treatments in the same hair sample caused even more pronounced structural alterations. Scanning electron microscopy analysis has also demonstrated that each of the individual treatments caused a different morphological deformation pattern at the hair surface, supporting the results observed by Raman and infrared techniques.