Lychee Peel Colorant as a Sustainable Natural Product for Textile Dyeing: Statistical Optimization, Mordanting, and Colorfastness Evaluation

Abstract

Background There is a growing recognition of natural products from agro-waste as sustainable alternatives to synthetic dyes for textiles. Lychee peel (Litchi chinensis Sonn.), which is rich in polyphenolic substances in the skin, might be an environmentally friendly dye resource for textiles. Objective The purpose of this study was to explore lychee peel as a natural dye for silk, by investigating aqueous, acidic and alkaline extracts, optimizing the parameters for the selected dyeing process and evaluating chemical and bio-based mordanting methods. Methods Lychee-peel colorants were extracted using aqueous, acidic, and alkaline media. The extracts and silk fabric were microwave-treated for 2–10 min before dyeing. Selected dyeing variables were optimized using classical central composite design. Color strength (K/S), CIE L * a * b * coordinates, Fourier-transform infrared spectra, surface morphology, and colorfastness to washing, rubbing, and light were evaluated. Chemical and bio-based mordants were applied through pre- and post-mordanting. Results The alkaline extract provided the highest chromatic intensity. The value of K/S increased from 5.5034 to 6.9647 when the microwave exposure was 6 min, while the maximum value of aqueous and acidic extract was 2.3779 and 2.4057, respectively. The statistical model explained the significance of dyeing variables. The dye bath pH and temperature had a significant effect on K/S and interactions between pH and time and time and temperature were found. Among the bio-mordants tested, Marigold gave highest color intensity with K/S value of around 13.96. FTIR spectra showed no major changes in the principal functional groups of silk after microwave treatment. The reported washing, rubbing, and light fastness ratings were 4/5 under the selected mordanting conditions. Conclusion Lychee peel showed laboratory-scale potential as a natural colorant for silk. Alkaline extraction, controlled microwave treatment, process optimization, and bio-mordanting improved shade development and produced good reported fastness performance. Further work should evaluate colorant composition, treatment reproducibility, wastewater impacts, and industrial-scale feasibility.