Optimization of dyeing process variables for eco-friendly dyeing of cotton fabric with babul bark extract as a natural dye and gallnut extract as a bio-mordant

In the present study, cotton fabric has been dyed with aqueous extract of babul bark (Acacia nilotica) using gallnut (Quercus infectoria) as bio-mordant containing hydrolyzable tannins like gallic acid, elagic acid and polyphenolic gallotannins to produce light yellow color. On the other hand when gallnut bio-mordanted cotton is subsequently dyed with babul bark extract as a natural dye containing similar but non-hydrolyzable tannin-rich color component including small amount of catechin and epi-gallo-catechin, it produces a medium to deep brown color through formation of giant insoluble colored complex of cotton-gallotannins (gallnut)-catechin/epigallocatechin and other color components present in babul bark extract. The process variables for extraction, pre-mordanting and dyeing have been optimized to standardize this dyeing technique. Scattered CDI values for dye-bath pH and dye concentration identified them as the most important dyeing parameters that need to be controlled for obtaining uniform dyeing. High UPF value of upto 35 rendered by application of both gallnut and babul bark through preferential absorption of UV light by the gallotannins in both gallnut and babul bark indicates good UV protection properties of dyed cotton fabrics.