Extraction and Characterization of Natural Dyes from Agricultural Waste for Textile Applications

The textile industry generates substantial environmental impacts through synthetic dye production and wastewater discharge, motivating renewed interest in natural colorants derived from renewable agricultural sources. This research investigates the extraction, characterization, and application of natural dyes obtained from four agricultural waste materials: onion skin, grape pomace, green tea processing residues, and turmeric byproducts collected from food processing facilities in the Kanto region of Japan. Three extraction methodologies were systematically compared: conventional aqueous extraction, ethanol-assisted extraction, and ultrasonic-assisted extraction at varying temperatures between 40 and 80 degrees Celsius. The experimental program was conducted at the Natural Products Laboratory of Tokyo Institute of Applied Sciences between April and November 2023. Dye yields ranged from 8.3 to 42.3 milligrams per gram of dry waste material, with turmeric residues providing the highest extraction efficiency and ultrasonic-assisted methods generally outperforming conventional approaches across all source materials. Characterization through ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, and high-performance liquid chromatography identified quercetin derivatives as the primary chromophores in onion skin extracts, anthocyanins in grape pomace, catechins in green tea waste, and curcuminoids in turmeric residues. Application testing on cotton fabric demonstrated color strength values between 2.8 and 8.4 K/S units with wash fastness ratings of 3.2 to 4.1 on the standard five-point scale. Green tea extracts achieved superior fastness properties attributed to the chelating capacity of polyphenolic compounds with aluminum mordant. The findings establish that agricultural processing waste streams represent viable sources for natural textile dyes when appropriate extraction protocols and mordanting procedures are employed, offering circular economy opportunities that simultaneously address waste management challenges and demand for sustainable textile colorants.