Mechanical characterization of curly hair: Influence of the use of nonconventional hair straightening treatments.
OBJECTIVE
Hair straighteners are very popular around the world, although they can cause great damage to the hair. Thus, the characterization of the mechanical properties of curly hair using advanced techniques is very important to clarify how hair straighteners act on hair fibers and to contribute to the development of effective products. On this basis, we chose two nonconventional hair straighteners (formaldehyde and glyoxylic acid) to investigate how hair straightening treatments affect the mechanical properties of curly hair.


METHODS
The mechanical properties of curly hair were evaluated using a tensile test, differential scanning calorimetry (DSC) measurements, scanning electronic microscopy (SEM), a torsion modulus, dynamic vapor sorption (DVS), and Fourier transform infrared spectroscopy (FTIR) analysis.


RESULTS
The techniques used effectively helped the understanding of the influence of nonconventional hair straighteners on hair properties. For the break stress and the break extension tests, formaldehyde showed a marked decrease in these parameters, with great hair damage. Glyoxylic acid had a slight effect compared to formaldehyde treatment. Both treatments showed an increase in shear modulus, a decrease in water sorption and damage to the hair surface.


CONCLUSIONS
A combination of the techniques used in this study permitted a better understanding of nonconventional hair straightener treatments and also supported the choice of the better treatment, considering a good relationship between efficacy and safety. Thus, it is very important to determine the properties of hair for the development of cosmetics used to improve the beauty of curly hair.
Faculty of Pharmaceuticals Sciences of Ribeirão Preto, Univeristy of São Paulo, Ribeirão Preto, São Paulo, Brazil.
M G A
MGA
Leite
Faculty of Pharmaceuticals Sciences of Ribeirão Preto, Univeristy of São Paulo, Ribeirão Preto, São Paulo, Brazil.
P M B G
http://orcid.org/0000-0001-6678-1207
PMBG
Maia Campos
D004202:Disinfectants / Q000494:pharmacology; D005557:Formaldehyde / Q000494:pharmacology; D006038:Glyoxylates / Q000494:pharmacology; D006197:Hair / Q000502:physiology* / Q000648:ultrastructure; D006203:Hair Preparations / Q000494:pharmacology*; D006801:Humans; D008855:Microscopy, Electron, Scanning; D013718:Tensile Strength
D004202:Disinfectants; D006038:Glyoxylates; D006203:Hair Preparations; D005557:Formaldehyde; C031150:glyoxylic acid
SEM analysis; dynamic vapor sorption analysis; formaldehyde; glyoxylic acid; hair straightener; tensile test; torsion modulus