Investigations of vegetable tannins as hair dyes and their interactions with pre-bleached hair fibres

Abstract

Objective: The aim of this work was to investigate an alternative hair-dyeing method with vegetable colourants as the tannins, as well as the impact of pre-treatment as the bleaching process. Methods: Untreated, 1, 2 and 3 times bleached hair tresses that were dyed with tannins in combination with metal salts were characterized. The wash fastness and the colour strength of the vegetable-dyed hair tresses were spectrophotometrically investigated. Results: To determine the colour strength KS and the wash fastness of vegetable-dyed and pre-bleached hair tresses, a three-dimensional colour coordinate system – CIELab – which describes the visual spectra is used. The distance between two colours in the CIELab colour space is expressed by ∆E-values, which are used to identify the wash fastness of the vegetable dye. The hair tresses that had been 3 times pre-bleached showed the highest colour strength and the best wash fastness. The fixation of the tannin–mordant complexes on the hair fibre proceeded effectively just when the hair tresses were bleached before the dying process. It is suggested that the sulphonic acid groups, which increase after bleaching hair, interact with the tannin–mordant hair dye and lead to stronger cross-links between keratinous fibres and tannin–mordant complexes. It was observed that the colour strength of the vegetable-dyed tresses correlates with the bleaching process. Conclusion: The presented results demonstrate that the fixation of the vegetable tannin–mordant dying solution on the hair fibres succeed effectively on pre-bleached hair tresses.