Eco-friendly dyeing of cotton fabric using used tea bag extracts: A comprehensive study on pH, fabric cationisation, and computational analysis

The present study aims to explore the eco-friendly dyeing of cotton fabric using extracts from used tea bags, without the need for any metal mordant. Additionally, this research delves into the intricate relationship between pH levels and fabric cationisation, exploring their combined impact on the functional properties of naturally dyed cotton samples. Preceding the dyeing process, the cotton fabric underwent cationisation through the application of 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC) at varying percentages. Subsequently, the fabric was dyed with tea liquor at different concentrations and pH levels. The ensuing investigation encompassed an assessment of color fastness and colorimetric attributes (CIELab, CIELch, ΔE, and K/S) of the dyed cotton fabrics. Furthermore, FTIR analysis was employed to augment our understanding of the dyeing process, while UV-Vis spectroscopy facilitated the quantification of exhaustion and fixation percentages. The results indicate that the highest exhaustion percentage of 88.6% was achieved at pH 13 for cationised fabric with a cationiser concentration of 55 g/L. In comparison, the non-cationised fabric exhibited an exhaustion percentage of 0.75%, while the mordanted (KAI(SO₄)₂.12H₂O) fabric showed 3.6%. Furthermore, the cationised fabric displayed excellent colour fastness to washing, rubbing, and perspiration (rated 4–5) compared to the non-cationised fabric. The stronger interaction calculated with density functional theory (DFT) between theaflavins, one of the primary colour components of tea dye, and cationised cellulose monomers explains the enhanced washing and rubbing fastness observed. The findings emphasize the significant influence of pH and fabric cationisation on dyeing and the functional properties of the dyed fabric.