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

Biodegradable sulphonated lignin (SL) can be used as a natural dye for the sustainable colouration of wool fabric. for producing brown shades on wool fabric, but the colourfastness to washing is only moderate, and the colour strength is also weak. In this work, wool fabrics were dyed with various concentrations of water-soluble sulphonated lignin using several sustainable mordanting agents to improve the colour yield and also the colourfastness to washing along with introducing new functional properties, such as UV protection capabilities. The colour yield of wool fabric dyed with lignin sulphonate using various mordanting agents was measured by reflectance spectroscopy. The Al and Ca mordants produced brown colour but the Cu and Fe mordants produced olive and grayish-brown colours respectively. The dyed fabrics exhibited high colour yield and enhanced colourfastness to washing. The dyed fabrics exhibited high colour yield, which increased with an increase in the lignin concentration and also showed improvement in colourfastness to washing by a grade. The highest colour strength was produced by wool fabric treated with 5% on the weight of fibre lignin sulphonate using Cu mordant at 35% on the weight of applied SL (ows). The Al and Ca mordants produced brown colour but the Cu and Fe mordants produced dark olive and dark greyish brown colours respectively. The colourfastness increased to Grade 4 for all the mordanting agents studied in this work. The Cu mordant provided the highest colour strength (4.21) for the fabric dyed with 5% (on the weight of fibre) lignin sulphonate at Cu mordant concentration of 25% on the weight of lignin sulphonate (ows) and increased the colourfastness to washing to Grade 4/5 for the fabric dyed with 5% lignin using Cu mordant concentration of 35% (ows). The results suggest that The developed method can be used for the sustainable dyeing of wool fabrics in the textile industry with high colour yield and colourfastness to washing for producing verities of colours.