Molecular Structural Basis of Hair Property Manipulation

Abstract

Human hair is an α-keratinous protein, with a complex hierarchical structure, with a two-phase system describing the intermediate filaments (IFs) and matrix. Disulphide bonds between cysteine residues are of particular importance to the cosmetics industry. These bonds are partially responsible for human hairs high tensile strength and ability to withstand high temperatures. High temperatures and brushing/pulling on the hair form different common treatments to hair, all of which can be damaging to the visual and textural properties of hair, subsequently, disulphide bonds are of great cosmetic importance. In this study, brown, untreated, straight, European (virgin) human hair undergoes a treatment in order to reduce and alkylate disulphide bonds, using different alkylating agents, (iodomethane, iodoethane, iodoacetic acid, iodoacetamide), over a variety of time periods (1, 3, 10 or 24 hours). Extent of alkylation was measured using high performance liquid chromatography (HPLC). It was shown that alkyl concentration increases with period of alkylation, with modified cysteine making up a maximum of 12% of the entire fibre in mol%. The trend was true for all alkylating agents used, regardless of size of charge. Thermal changes were seen to the hair using differential scanning calorimetry, with denaturation temperature increasing with modified cystine mol%. Denaturation enthalpy shows a disruptive and stabilising effect as alkyl concentration increases, varying with alkylating agent used. This disruptive and stabilising effect is also seen in measurements made for Young’s modulus and break strain with a disruptive effect seen at lower alkyl concentrations, followed by a stabilising effect with Young’s modulus and break strain being restored to a value near to the virgin hair reference value as modified cystine content increases. In addition to this, a variety of tensile parameters were plotted against one another, showing a high degree of correlation between these parameters. This was found to be true for all modified samples as well as virgin hair samples. As a result, only Young’s modulus and break strain were analysed in this study as no new information could be found by analysing correlated parameters.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Franz Wortmann (Supervisor) & Gabriele Wortmann (Supervisor)