Analyzing the lightfastness of Indigo and woad-dyed cotton using different reducing agents, lemon treatment and variation in dye concentration

Abstract

The synthetic indigo used to dye denim fades rapidly under sunlight, so improving lightfastness is important. Previously approaches were taken separately on different natural-dyed cotton by increasing the dye’s concentration and applying synthetic antioxidants to improve the lightfastness of dyed samples. Little study was done to enhance lightfastness on cotton dyed using natural indigo and woad dye with different reducing agents, applying natural antioxidant and increasing the dye concentration. So, this study focuses on improving the lightfastness of indigo and woad dyed cotton instead of using synthetic indigo dye for sustainable textile coloration along with fructose as a natural and thiourea as synthetic reducing agent, varying dye concentration from 3 to 7 g/l and applying natural antioxidants lemon’s raw juice after dyeing. FTIR analysis was done to confirm the presence of lemon’s raw juice after treatment. Delta E was used as a lightfastness parameter instead of using a grey scale rating for quantitative analysis. From the lightfastness results, lemon-treated and using 3 g/l dye concentration dyed samples most of the cases showed better lightfastness results along with a low color fading rate than untreated dyed samples. Besides, samples using thiourea dioxide have better lightfastness properties than samples using fructose. Further statistical analysis (i.e., bootstrapping for resampling) was also done to validate these results and those statistical models confirmed those decisions.