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The Principle of Synthesizing Tannin to Improve the Homochromaticity of Silk/Nylon Fabric

Key words: silk; nylon fabric; American instrument ; UV-1100; UV-1800

Src="http://i.bosscdn.com/blog/nophoto.gif" /></p> <p> Silk/nylon fabric is a type of multi-component textile that combines the natural properties of silk with the durability of nylon. Although both fibers can be dyed using acid dyes and 1:2 metal complex dyes, achieving uniform coloration in one bath is challenging due to differences in their chemical structure, functional groups, and dye affinity. When dyeing light or medium shades, nylon tends to absorb more dye than silk, resulting in a darker appearance. However, for deep colors, the lower amino group content in nylon leads to less dye uptake, making it appear lighter compared to silk. </p> <p> Research has shown that by selecting appropriate dyes and controlling the pH of the dye bath, the homochromaticity of silk/nylon fabrics can be significantly improved. One effective method involves adding a suitable dyeing assistant, such as synthetic tannins, which can reduce the dye absorption on nylon. This helps balance the color between the two fibers. Synthetic tannins have been successfully used in wool/nylon blends to enhance color consistency by reducing the amount of acid dyes absorbed by nylon. Similarly, they improve the color matching of nylon/cellulose blends by reducing direct and reactive dye uptake. </p> <p> It is believed that synthetic tannins can also be beneficial when applied to silk/nylon fabrics. By reducing the dye uptake on nylon, the color difference between silk and nylon can be minimized, leading to better overall color harmony. This study explores the application of synthetic tannins in the dyeing of silk/nylon fabrics using acidic and neutral dyes, with a focus on understanding how these tannins improve the homochromaticity of the fabric. </p> <h2>1. Test</h2> <h3>1.1 Materials and Dyes</h3> <p> The materials used include silk and nylon fabrics. The dyes tested are weak acid dyes such as Everacid A and Everacid N, along with weakly acidic yellow 6G, brilliant blue G, and brilliant blue 6B (commercially available). Neutral dyes like Isolan K (without sulfonic acid groups), Isolans (with one sulfonic acid group), and Isolan 2S (with two sulfonic acid groups) were also used. Other chemicals included Mesitol NBS (a synthetic tannin composed of aromatic sulfonic acid, hydroxy aromatic sulfone, and formaldehyde), acetic acid, and sodium acetate (all of analytical grade). </p> <h3>1.2 Dyeing Method</h3> <p> Equal weights of silk and nylon fabrics were dyed in the same dye bath to simulate the dyeing process of silk/nylon blends. The dyeing conditions included a concentration of 2% (owf) for the dye, 1.5% (owf) for synthetic tannin, a pH adjusted using acetate/sodium acetate, and a liquor ratio of 50:1. The dyeing process involved heating the bath from 40°C to 95°C, maintaining it at 95°C for 60 minutes, followed by washing and drying. </p> <h3>1.3 Synthetic Tannin Adsorption Test</h3> <p> Both silk and nylon fabrics were treated with the synthetic tannin solution at 60°C, pH 5, and a liquor ratio of 40:1 for 40 minutes. Afterward, the samples were rinsed with water and air-dried. </p> <h3>1.4 Dyeing Percentage (E) and Color Measurement</h3> <p> The dyeing percentage was determined using a UV-1800 spectrophotometer (from a Chinese manufacturer) via the residual liquid colorimetric method. The absorbance values before and after dyeing were measured at the maximum absorption wavelength, and the dyeing percentage was calculated based on these values. The adsorption of synthetic tannin on the fibers was also analyzed by measuring the absorbance of the residual liquid and comparing it to a standard curve. </p> <p> The K/S value was measured using an UltraScan PRO colorimeter under D65 illumination and a 10° viewing angle. The homochromatic balance value (K) was calculated using the formula: K = (K/S)n / (K/S)s. When K=1, the colors of silk and nylon are the same; when K>1, nylon appears darker; when K<1, silk appears darker. The closer K is to 1, the better the homochromaticity. </p> <h2>2. Results and Discussion</h2> <h3>2.1 Application of Synthetic Tannin in Dyeing of Silk/Nylon Fabric</h3> <h4>2.1.1 Effect of Synthetic Tannin on Dyeing of Different Dyes</h4> <p> The K/S values of silk/nylon fabrics dyed with and without synthetic tannins were measured. The results showed that most dyes produced higher K/S values for nylon compared to silk, indicating poor homochromaticity. However, after adding synthetic tannin, the K/S values of both fibers became more balanced, improving the color match. For example, the addition of tannin reduced the K/S value of nylon while increasing that of silk, resulting in a more even color. </p> <h4>2.1.2 Effect of Synthetic Tannin Amount on Homochromaticity</h4> <p> The relationship between the amount of synthetic tannin and the K/S values of silk and nylon was studied. As the tannin concentration increased, the K/S value of nylon decreased, while that of silk increased. At optimal concentrations, the K/S values of both fibers became similar, leading to a more uniform color. For instance, 1.2% (owf) of tannin was sufficient to achieve equal coloration for Everacid Red NB, while higher amounts were needed for dyes like Everacid Blue N-RL due to their smaller molecular size and simpler structure. </p> <h3>2.2 Mechanism of Improving Dyeing and Homochromaticity with Synthetic Tannin</h3> <p> Synthetic tannins may interact with dyes in the dye bath, forming complexes or adsorbing onto the fiber surface. This interaction affects the dye uptake and distribution between silk and nylon, ultimately influencing the homochromaticity of the fabric. Further research is needed to fully understand the mechanisms behind this effect and optimize the use of synthetic tannins in dyeing processes. </p> <p> Keywords: silk; nylon fabric; American instrument; UV-1100; UV-1800 </p> </dt> </div> <div class=

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