The environmental stakes are considerable. Conventional textile coloration consumes an estimated 100 to 200 liters of water per kilogram of fabric, and the resulting effluent, loaded with synthetic dyes and chemical auxiliaries, is frequently discharged into rivers, threatening aquatic ecosystems. Regulatory frameworks such as Zero Liquid Discharge and Zero Hazardous Chemicals initiatives have pushed the industry toward cleaner processes, but most alternatives still rely on synthetic colorants that carry their own hazards. When dyed synthetic fibers degrade at the end of their life, they can release toxic dye fragments into soil and water. The Wyoming team, led by Solaiman Bin Ali, set out to eliminate both problems at once: no water, and no synthetic dye.

Dope dyeing itself is not new. The approach involves dissolving a textile polymer in a suitable solvent, dispersing the dye into that solution, and then forming solid fibers from the mixture, either by melt spinning or solution spinning. Previous studies have doped yellow and green pigments into polylactic acid, and phthalocyanine dyes into recycled polyester, with encouraging fastness results. But melt spinning carries drawbacks, including the energy cost of high temperatures, the difficulty of maintaining solution viscosity, and challenges in changing shades during production. Electrospinning, which solidifies polymer chains using electrostatic forces, offers a gentler route: colorants become trapped in the amorphous regions of the polymer, process parameters are flexible, and no water or extra chemicals are needed. Until now, however, nearly all dope dyeing studies relied on synthetic dyes.

The choice of weld dye is what makes the study distinctive. Weld has been used since antiquity to produce brilliant yellows on wool and silk, and its active colorant is luteolin, a small flavonoid molecule studded with hydroxyl functional groups. Those hydroxyls matter, because they can potentially form hydrogen bonds with the residual hydroxyl groups on cellulose acetate, a widely used textile polymer in which most hydroxyl sites are acetylated. The researchers ground the weld dye into a dry powder and added it at 6 percent by weight to a solution of 17 percent cellulose acetate dissolved in a 2:1 mixture of acetone and dimethylformamide. The mixture was stirred, sonicated for two hours, and conditioned for twelve hours before electrospinning.

The spinning process itself was carefully controlled. The polymer solution was loaded into a syringe with a 21-gauge needle and subjected to a voltage of 12.5 kilovolts, with a flow rate of 1.5 milliliters per hour, a collector rotating at 300 revolutions per minute, and a needle-to-collector distance of 15 centimeters. Relative humidity was held at 30 percent and temperature at 22 degrees Celsius. Once the nanofiber web reached a thickness of 1.5 millimeters, it was dried at 80 degrees Celsius for 48 hours. As a control, the team also conventionally dyed woven cellulose acetate fabric using tannic acid as a mordant, following a standard dye bath protocol with a 6 percent dye application.

One of the study’s most revealing observations came from simply watching the dope solution sit in a flask. Immediately after sonication, the solution appeared uniformly yellow, suggesting the dye was well dispersed. But over the course of an hour, the picture changed dramatically. The upper portion of the solution faded to a light tint while the lower portion darkened, indicating that most of the weld dye was precipitating out rather than remaining dissolved. By the end of the observation period, roughly nine milliliters of the ten-milliliter sample had settled. The researchers attribute the partial solubility to hydrogen bonding between the dye’s hydroxyl groups and the limited free hydroxyl groups on cellulose acetate, most of which are blocked by acetyl groups. Only a small fraction of the dye stayed in solution long enough to travel through the needle during electrospinning.

That limited solubility explains the study’s central trade-off. Spectrophotometric analysis using the CIE Lab* color space showed that the dope-dyed nanofibers did develop a yellow shade, with the b* value, which quantifies yellowness, rising from -0.32 for undoped nanofibers to 2.37 for doped ones. But the conventionally dyed woven fabric reached a b* value of 12.59, a far more intense yellow, and a color strength, or K/S value, of 2.1 compared with the lower value of the doped nanofibers. The result is somewhat counterintuitive, because nanofibers have enormous specific surface area and would theoretically be expected to hold more dye than conventional fibers. In dope dyeing, however, coloration depends entirely on how much dye is actually dissolved in the spinning solution and carried into the fiber, not on how much can be deposited on the surface afterward.

Scanning electron microscopy and infrared spectroscopy told the deeper story. SEM images of the conventionally dyed fabric revealed large dye particles sitting on the fiber surface, evidence that the weld dye had deposited without forming strong bonds. The dope-dyed nanofibers, by contrast, showed no visible particles at all, suggesting the dye was dispersed at the molecular level within the polymer rather than resting on top of it. Fourier transform infrared spectroscopy backed this up: the doped nanofibers showed broadened hydroxyl stretching bands in the 3200 to 3600 per centimeter region, consistent with hydrogen bonding between the dye and the polymer, along with an intensified carbonyl peak near 1756 per centimeter and a deeper C-O peak near 1214 per centimeter. Those changes hint at something even stronger than hydrogen bonding: possible transesterification, in which the dye’s hydroxyl groups react with the polymer’s acetyl groups to form new covalent ester linkages, chemically locking the dye into the fiber structure.

The wash fastness results were the study’s most striking finding. Following the AATCC 61-2013 1A standard laundering test, the conventionally dyed fabric scored an average grey scale rating of 2, indicating poor durability, a consequence of weld dye’s inherently low affinity for cellulose acetate and the absence of strong bonding without an effective mordant. The dope-dyed nanofibers scored an average of 4, indicating good color retention, despite using no mordant at all. The explanation lies in the molecular integration revealed by the spectroscopy: dye that is entrapped within and chemically bonded to the polymer chains simply cannot wash out the way surface-deposited dye can. For a natural dye class long criticized for poor fastness, that is a meaningful advance.

The authors are careful to frame the work as a feasibility study rather than a finished industrial process. The color intensity of the dope-dyed nanofibers remains well below that of conventional dyeing, and improving it will likely require enhancing the dye’s solubility in the spinning solvent or increasing the fraction of dye that survives the journey from solution to fiber. Still, the implications are considerable. The process combines fiber formation and coloration in a single waterless, chemical-free step, aligns with Zero Liquid Discharge and Zero Hazardous Chemicals principles, and replaces a synthetic colorant with a plant-derived one whose degradation products are far less concerning. If follow-up research can close the color intensity gap, the humble weld plant, a dye source known to ancient dyers, could find itself at the center of a very modern sustainability story.

Subject of Research: Waterless dope dyeing of electrospun cellulose acetate nanofibers with natural weld dye

Article Title: Feasibility study of dope dyeing nano cellulose acetate with weld dye

Article References: Ali, S. B., Harmon, J., & Brant, J. (2026). Feasibility study of dope dyeing nano cellulose acetate with weld dye. Discover Chemistry, 3(1), Article 532. https://doi.org/10.1007/s44371-026-00997-8

Image Credits: AI Generated

DOI: 10.1007/s44371-026-00997-8

Keywords: dope dyeing, cellulose acetate, weld dye, electrospinning, nanofibers, natural dyes, textile coloration, waterless dyeing, wash fastness, FTIR spectroscopy, sustainability, green chemistry