Valorization of Sulfonated Kraft Lignin as a Natural Dye for the Sustainable Dyeing of Wool Fabrics: Effect of Peroxide Oxidation

Abstract

Lignin is an abundant and complex biopolymer with inherent color but has only a few applications. It has the potential to replace synthetic acid dyes for the coloration of wool fibers in brown shades, as traditional dyeing with acid dyes produces toxic effluent needing costly treatment. In this work, the valorization of sulfonated lignin was explored by using it as a natural dye for the coloration of wool fabrics alone and with hydrogen peroxide (H 2 O 2 ). The dyed fabrics were characterized by reflectance and diffuse reflectance spectroscopies to assess the color yield and ultraviolet (UV) protection performance, respectively. The dyed fabrics exhibited reasonably good color yield and satisfactory colorfastness to washing (Grade 3/4), which improved to Grade 4 by the oxidation treatment with H 2 O 2 . The scanning electron microscopy (SEM) images show that when fabrics are dyed alone with lignin, deposition of lignin particles is visible on the fiber surface, but with hydrogen peroxide, no deposition of lignin is visible on the fiber surface, and the color strength of the fabric became almost double. The UV light transmission through the fabric decreased from 6.73 and 13.23% at 311 and 365 nm to 2.19 and 5.23%, respectively. The attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra of the dyed fabrics showed increased absorption of lignin sulfonate by the fabric, suggesting depolymerization of lignin by H 2 O 2 to smaller macromolecules easing absorption into the wool fiber. Lignin sulfonate could be a cheap and sustainable alternative to harmful synthetic dyes for producing brown shades on wool fabric.

Valorisation of sulphonated lignin as a dye for the sustainable colouration of wool fabric using sustainable mordanting agents: enhanced colour yield, colourfastness, and functional properties

“…Except for Ca, all other mordanting agents provided very good colourfastness to washing as the fastness grade was 3–4, much better than the colourfastness to washing of wool fabrics dyed with SL without using any mordanting agent. 30 The colourfastness to washing increased by one grade compared to the wool fabric samples dyed with SL alone. The colourfastness to staining for different types of fibres was also quite good except against nylon fabric, which is also a polyamide fibre like wool fibre.…”

“…For 1% (owf) SL, the colour yield achieved with Cu mordant was 1.7, equal to the wool fabric treated with 8% SL without using any mordanting agent, as reported in our previous article. 30 All other mordants produced similar colours except the Cu and Fe mordants, which provided considerably higher colour strength compared to the fabric dyed with other mordants. When the SL dosage was increased to 3% (owf), the colour yield for the Cu mordant increased to 3.13.…”

“…In our previous work, we reported the colour yield and colourfastness to washing of wool fabric dyed with various concentrations of low-molecular-weight sulphonated lignin (SL) without and with hydrogen peroxide. 30 The colourfastness to washing was reasonably good, but the colour strength produced by the dyed fabric was poor and produced only a brown colour shade with tonal changes. These properties of the SL-dyed fabric need further improvement for industrial application.…”

“…The dyeing was carried out at pH 3 as our previous work showed that the maximum absorption of SL was achieved at that pH. 30 Fig. 3 shows the effect of SL concentration on the colour strength of wool fabric using a mordanting agent concentration of 25% (ows).…”