Thermal analysis and synergistic tools for the development of a semi-permanent hair straightening technology

This research was carried out with the objective to develop a thermal analysis protocol into a method of damage assessment and claims support for a new semi-permanent hair straightening technology. The investigation determined the effects of the treatment on hair fibre composition and properties using Modulated Differential Scanning Calorimetry (MDSC) [1], Fourier Transform Infrared Spectroscopy (FTIR) [2], Gel Electrophoresis (SDS-PAGE) [3] and curl retention tests [4]. The effects of the new cysteamine treatment are compared with effects of a standard thioglycolate treatment and the daily use of straightening irons. Virgin, Caucasian hair was treated once with each chemical treatment and washed every day for 84 days. In a parallel study, hair was washed and straightened repeatedly using a standardised protocol at 190oC for 84 days. Samples were taken after 2, 28, 56 and 84 days for analysis by MDSC in water, ATR- and Trans-FTIR. Separate samples were treated once and subjected to curl retention tests and protein analysis. DSC measurements in water yield the keratin denaturation enthalpy (ΔHD), which relates to the thermal stability of the keratin intermediate filaments (KIFs), and the denaturation temperature (TD), which relates to the properties of the keratin associated-proteins (KAPs). The results show that chemical and thermal straightening cause a reduction in α-helix content and matrix viscosity. FTIR measurements give information on the formation of cysteic acid in the cuticle cells and the cortex. ATR-FTIR showed that the cysteamine–based treatment produces less cysteic acid in the cuticle layers than the standard treatment. Curl retention and SDS-PAGE were used to show the variability in the efficacy of the cysteamine treatment related to the heterogeneity of human hair. The results from both tests show that an individual’s hair will react with the product to a different extent, depending on the extractability of the keratin protein groups.In conclusion, we deduce that all straightening techniques, chemical and thermal, have a pronounced effect on the structural and chemical properties of hair fibres. These effects can be used to further develop and optimize this and related products. DSC has been shown to be an integral synergistic technique for the investigation of changes to hair morphology.This research was supported by the UK Technology Strategy Board under the Knowledge Transfer Partnership scheme.Cyril Keattch Award, Thermal Methods Group, Royal Society of Chemistry, 2014.[1] F.J. Wortmann, G. Wortmann, J. Marsh, K. Meinert. J. Struct. Biol., 177 (2012) 553. [2] V. Signori, D. Lewis. Int. J. Cosmet. Sci., 19 (1997) 1-13.[3] A.M. Zalfen, G. Wortmann, F.J. Wortmann. SOEFW Journal, 131 (2005) 40.[4] F.J. Wortmann, M. Stapels, L. Chandra. J Appl.Polym.Sci., 113 (2009) 3336.