A study of the effect of organic acids (gallic acid and ascorbic acid) on the coloration and functionalization of wool yarns with Millettia laurentii sawdust natural dye

Abstract

Wastewater from the textile industry, especially the dyeing sector, is a major contaminant for aquatic ecosystems. Synthetic dye compounds and metal salts from leftover mordant and dyeing baths are washed into rivers, endangering aquatic life and the environment. In regards to the current study’s examination of Millettia laurentii sawdust’s potential as a natural color source, eco-friendly organic acids (gallic acid and ascorbic acid) were studied in conjunction with small amounts of metal salts (aluminum sulfate, stannous chloride, copper sulfate, and ferrous sulfate) for enhancing the color shade palette with simultaneous functionalization (antimicrobial and UV-protection) of wool yarns. The effects of metal salts up to ecologically permissible concentration limits on the dyeing and functional properties were assessed in combination with organic acids. The study focused on optimizing dyeing variables including pH (2–8), temperature (65–95 °C), dye concentration (25–125% o.w.f.), and dyeing time (15–90 min) using a one-factor-at-a-time (OFT) optimization by determining the color depth (K/S) values on the wool yarns. The optimized dyeing conditions were pH of 4, temperature of 95 °C, dye concentration of 75.0% (o.w.f.), and dyeing time of 60 min. The color characteristics (CIEL*a*b*c*ho) and fastness (Wash, rub, and light) properties are evaluated comparatively against control dyed wool yarns using standard methods. The antimicrobial activity of control dyed and mordanted dyed wool yarns was evaluated in terms of the percentage microbial reduction of bacterial colonies. Metal salts especially ferrous sulfate in conjunction with gallic acid (Fe/GA) provided the highest average color strength (13.50) with a maximum percentage microbial reduction of 96.67%. UV protection ability was assessed by an Australian and New Zealand standards (AS/NZS 4399: 1996) method in terms of UPF values. UV protection levels were significantly improved by using binary combinations of organic acids and metal salts with the maximum protection offered by Fe/GA (97.66) and Sn/GA (97.90). Dyeing outcomes were significantly impacted by the chemical structure of organic acids (gallic acid and ascorbic acid) and the type of metal salts; the research proposes a more environmentally friendly natural dyeing process for the textile industry.