Abstract:

Objective The exceptional benefits of wool fibers in terms of warmth retention, air and moisture permeability, and distinctive garment appearance make the wool fibers appealing. The value of finished wool clothing can be increased by using natural dyes to color the wool fibers. Natural dyes' limited color gamut, however, prevents them from being widely used due to issues in printing and dyeing wool fibers.
Method In order to enrich the color gamut of wool fibers dyed with natural dyes, natural red, yellow and blue, the three primary dyes, were chosen to dye wool fabrics and fibers with the one bath dyeing based on the use of fiber color matching method. The color prediction of fabric dyed with mixed dyes and mixed colored fibers was made based on Kubelka-Munk single constant theoretical model and Stearns-Noechel model, respectively.
Results The pH values have an effect on the depth of shade(K/S) for wool fibers colored with natural dyes(as shown in Tab. 1). The K/S value of the sample colored with natural red and blue dyes was increased from 3.89 to 17.82 and from 2.07 to 10.73 respectively as the pH value reduced from 4 to 2, while the sample dyed with natural yellow dye was decreased from 3.62 to 1.51 as the pH value decreased from 4 to 2. When the dye solution comprises natural red dyes, the hue angle h value of the fabric dyed using the one bath dyeing method ranged in 0°-24° and 324°-360°. The brightness value L^* of the mixed color fiber system was higher than that of fabric dyed using the one bath dyeing method, the color saturation value (C^*) decreased, and the hue angle range increased when the ratio of each dye used in the one bath dyeing method was equal to the ratio of the fiber dosage in the mixed colored fiber system. This may be because each fiber is dyed separately before being mixed, reducing dye competition and expanding the color gamut of woolen clothing dyed with natural dyes. The K/S curve of fabrics dyed using the one bath dyeing method matches the fitting curve by the Kubelka-Munk single constant theoretical model (Fig. 3), demonstrating a linear relationship between the K/S value of wool fabric dyed with mixed natural dyes and the K/S value of dyed with the single red, yellow, and blue natural dyes. Additionally, the reflectance curve of the mixed colored fiber was fitted using the Stearns-Noechel model. Reflectance change of the mixed colored fibers in the 400-700 nm wavelength range was almost in line with the reflectance curve determined using the Stearns-Noechel model(as seen in Fig. 4).
Conclusion The CIELAB color gamut space showed non-uniform distribution of the color coordinate of wool fabric dyed using the one bath dyeing method. Natural red dyes have a greater affinity for fibers than yellow, and blue natural dyes. Across comparison to wool fabric colored using the one bath dyeing method, the color coordinate of mixed colored fiber was spread more evenly in the color gamut space. The hue angle value of mixed colored fiber ranged in 0°-50° and 316°-360°. Using the one bath dyeing method and mixed colored fiber treated with natural dyes respectively, the Kubelka-Munk model and the Stearns-Noechel model could be used to predict the color of wool fabrics. This study also suggests novel approaches for further enhancing production efficiency and lowering color matching costs.

Key words: natural dye, wool fiber, color matching, Kubelka-Munk single constant theoretical model, Stearns-Noechel model, color gamut space