Fruit Peel Extracts Replace Toxic Chemicals in Cotton Discharge Printing

Every year, the textile industry throws away mountains of fruit waste while simultaneously pumping hazardous chemicals into the environment through one of its oldest decorative techniques: discharge printing. Now, a team of researchers at Bangladesh University of Textiles in Dhaka has shown that the discarded peels of oranges and pineapples, boiled in plain water, can do the work of some of the most toxic reducing agents in the textile chemist’s toolkit. In a study published in Discover Chemistry, Sk. Mohammad Raafi, Zahidul Islam, and Dwip Kumar demonstrate that aqueous extracts of mandarin orange and pineapple peels can strip color from reactive-dyed cotton fabric with efficiencies that rival, and in one case exceed, conventional synthetic reducers. The finding could point the way toward a bio-based route for a printing style that has long depended on formaldehyde-releasing compounds and sulfur-based salts.

Discharge printing is a subtractive art. Rather than adding pigment to undyed cloth, the printer applies a paste to fabric that has already been dyed a uniform shade, and the paste chemically destroys the dye in selected areas. The result is a crisp white or differently colored pattern emerging from a solid ground. The chemistry hinges on breaking the chromophore, the light-absorbing part of the dye molecule, which in the reactive azo dyes commonly used on cotton is a conjugated system built around an azo linkage of two nitrogen atoms joined by a double bond. Reducing agents donate electrons to this linkage, cleaving it and collapsing the conjugated system, so the molecule no longer absorbs visible light and the fabric appears white where the paste was applied.

The industry’s preferred reducers, however, come with a heavy environmental and toxicological price. Thiourea dioxide, sodium sulfoxylate formaldehyde, and sodium dithionite are the workhorses of reductive discharge, but conventional discharge pastes typically contain 20 to 30 percent hazardous chemicals per printing cycle. Sulfoxylate formaldehyde compounds release formaldehyde, a human carcinogen associated with nasal sinus and nasopharyngeal cancers. Sodium dithionite generates non-regenerable oxidation products such as sulfite and sulfate that complicate the disposal of residual paste and wash water. Stannous chloride formulations can introduce heavy metal ions and decompose to produce corrosive hydrogen chloride, while other by-products including carbon monoxide, sulfur dioxide, and zinc oxide add to the pollution burden. Oxidative alternatives such as potassium permanganate risk damaging the cotton substrate itself, and ozone treatment, though gentler, produces blurry printed outlines.

The Bangladesh team’s insight was to exploit the phytochemical wealth of fruit peels that are normally discarded as waste. Orange peels account for 30 to 50 percent of the fruit’s mass and pineapple peels for 40 to 50 percent, and both are rich in polyphenols, flavonoids, and ascorbic acid. These compounds are natural electron donors, which is precisely the defining property of a reducing agent. In the discharge paste, the polyphenols and flavonoids transfer electrons to the azo bonds of the reactive dye under alkaline conditions, breaking the conjugated system responsible for the color in much the same way synthetic reducers do, but with far lower ecotoxicity. Previous studies had already shown that antioxidant-rich extracts from banana, orange, pineapple, watermelon, and papaya peels could reduce and solubilize vat dyes, but their use in reactive discharge printing on cotton remained largely unexplored.

To prepare the extracts, the researchers separated the peels, dried them at 60 degrees Celsius for 24 hours, ground them into a moderately fine powder, and extracted them with distilled water at a 1:3 weight-to-volume ratio at 95 degrees Celsius for 30 minutes in a laboratory dyeing machine. After filtration, the orange peel extract and pineapple peel extract were formulated into white discharge print pastes alongside a synthetic thickener, urea as a hygroscopic agent, and soda ash to maintain the alkaline conditions needed both to activate the reducers and to promote hydrolysis of the covalent bond between the reactive dye and the cellulose fiber. The pastes were screen-printed onto cotton knit fabric dyed with two commercial vinyl sulfone reactive dyes, Remazol Ultra Carmine and Remazol Navy, then steamed at 105 degrees Celsius for 10 minutes and washed through a multi-step cycle.

Infrared spectroscopy provided the first line of chemical evidence. Both extracts showed broad absorption bands near 3355 inverse centimeters, consistent with hydroxyl stretching from phenolic and alcoholic groups, and a band around 1651 inverse centimeters attributable to carbonyl stretching, a functional profile consistent with phytochemicals capable of reducing activity. When the researchers compared the spectra of dyed fabrics before and after discharge printing, they found noticeable increases in transmittance at dye-related absorption bands, particularly in the fingerprint region between roughly 1500 and 600 inverse centimeters, where aromatic, sulfonate, and carbon-sulfur vibrations of the dye structure reside. The weakened or eliminated dye-associated signals indicated that both extracts had genuinely altered the chromophores in the printed areas rather than merely masking them.

The quantitative results were striking. On fabric dyed with the carmine shade, pineapple peel extract achieved a color strength reduction of 95.60 percent, slightly outperforming thiourea dioxide at 95.36 percent and sodium dithionite at 95.21 percent, while orange peel extract reached 93.01 percent. On the navy shade, the conventional agents led, with sodium sulfoxylate formaldehyde achieving 94.78 percent reduction, followed by thiourea dioxide and sodium dithionite, while orange peel extract managed 92.87 percent and pineapple peel extract 89.63 percent. Crucially, blank print pastes without any reducing agent produced reductions of only 9.46 and 10.45 percent on the two shades, confirming that the fruit extracts themselves were responsible for the discharge effect. The carmine dye discharged more readily than the navy dye across all treatments, likely because its chromophoric system was less resistant to the reducing environment.

Whiteness told a more nuanced story. Conventional reducers generally produced brighter, whiter discharged areas, with whiteness index values on the navy-dyed fabric exceeding 100 for all three synthetic agents, compared with 57.16 for orange peel extract and 45.38 for pineapple peel extract. The researchers note that the whiteness index depends on the final reflectance balance and chromaticity of the surface rather than simply on the percentage of dye removed, so a fabric can discharge well yet retain a slight tint that lowers its measured whiteness. The superior and more reproducible whiteness of the synthetic agents may reflect their controlled synthesis and purification, whereas natural extracts vary in composition with fruit source, maturity, and extraction efficiency. Mechanical testing showed moderate but acceptable losses of bursting strength, ranging from 14.73 to 21.65 percent relative to the original undyed fabric’s 217.60 kilopascals, with pineapple peel extract actually preserving strength better than several conventional agents on the navy-dyed fabric.

The study’s authors are careful to frame the comparison honestly: the amounts of the conventional reducers were optimized across multiple trials to achieve visually similar discharge effects, so the results reflect practical performance rather than an exact equal-dose chemical comparison. Even so, the message is clear. Water extracts of two abundant fruit wastes, prepared with nothing more elaborate than drying, grinding, and boiling, delivered discharge performance comparable to optimized doses of thiourea dioxide, sodium sulfoxylate formaldehyde, and sodium dithionite, while avoiding formaldehyde release, heavy metals, and problematic sulfur-based effluent. As the textile industry faces mounting pressure to adopt circular and sustainable processing, the prospect of turning kitchen-scale waste into a functional printing chemical is exactly the kind of elegant, low-tech solution that could travel quickly from the laboratory bench to the print floor, transforming both the industry’s waste stream and its chemical one at the same time.

Subject of Research: Use of orange and pineapple peel extracts as natural reducing agents for sustainable discharge printing on reactive-dyed cotton fabric

Article Title: Discharge printing on cotton fabric using fruit peel extracts as natural reducing agents

Article References: Raafi, S. M., Islam, Z., & Kumar, D. (2026). Discharge printing on cotton fabric using fruit peel extracts as natural reducing agents. Discover Chemistry, 3(1), Article 568. https://doi.org/10.1007/s44371-026-01019-3

Image Credits: AI Generated

DOI: 10.1007/s44371-026-01019-3

Keywords: discharge printing, cotton fabric, natural reducing agents, orange peel extract, pineapple peel extract, reactive dyes, sustainable textiles, fruit waste valorization, phytochemicals, azo dye reduction, textile chemistry, green chemistry