Revitalisation of natural dyes: Red shades of textiles dyed with Rubia tinctorum under different process parameters

Abstract

The demands of modern life and industry tend toward environmentally sound and sustainable processes in all areas of human activity, including the textile industry. In response to this demand, natural dyes, which had fallen into oblivion at the end of the 19th century, gained popularity as an acceptable alternative to synthetic dyes. The natural dye obtained from the plant Rubia tinctorum belongs to the group of acid-mordant dyes. The chemical structure of the main pigment, alizarin, and the method of binding it to fiber are described in the paper. Basic botanical and agronomic data are presented, as well as the history of Rubia tinsctorum dyeing and the possibilities of its modern application. Dyeing of wool and silk fabrics was carried out at different pH values and with different mordants (without mordant and with aluminum, copper, and iron). After dyeing, spectrophotometric analysis of the aqueous solutions of Rubia tinctorum was performed, and the color parameters of the dyed samples were determined spectrophotometrically. A test of washing and sunlight fastness was performed and the color difference determined spectrophotometrically was revealed. Considering the obtained results, an optimal dyeing procedure with the Rubia tinctorum plant is recommended. By dyeing wool and silk material with different process parameters, a wide range of red tones with h values from 30° (red part of the spectrum) to 70° (yellow part of the spectrum) was obtained. In combination with different brightness and chromaticity, wool and silk textiles with orange, pink, red and burgundy tones of satisfactory fastness were obtained, ready for the challenges of the market.