Wei Zhang (Department of Lightweight Engineering, Yancheng Textile Vocational and Technical College, Yancheng, Jiangsu 224005, China)
Abstract: Traditionally reduced indigo dyes are easy to damage silk fibers and are not suitable for dyeing silk fabrics. The dyeing of silk fabrics is studied by using edible indigo pigment to achieve the dyeing effect of reducing indigo. The results showed that under the condition of dye concentration of 0.4 g/L, the optimal dyeing conditions of indigo blue silk fabric were: pH6, electrolyte sodium sulfate concentration 15 g/L, dyeing temperature 80 °C, dyeing time 60 min. After dyeing, the hue blue pigment phase is close to the reduced indigo, and the indigo effect after dyeing the silk fabric is achieved. Under the optimal process conditions and after simple fixing treatment, the dyeing rate, leveling property and color fastness of the silk fabric after the dyeing of the silk fabric reached the processing and taking requirements.
Key words: indigo blue; silk fabric; color fastness; leveling property CLC number: TS195.6 Document code: A Article ID:1001-7003(2012)11-0015-03
Silk is a protein fiber. The molecular structure of silk fiber contains both acidic groups (-COOH) and basic groups (-NH2-OH), which are amphiphilic. Both acid and alkali promote the hydrolysis of silk fiber, and the degree of hydrolysis is closely related to the pH of the solution, the temperature of the treatment and the concentration of the solution. The effect of acid on silk fibroin is weaker than alkali. At present, silk fibers are mainly dyed with acid dyes and reactive dyes.
The molecular structure of the reduced indigo contains a carbonyl group. When dyeing, it is necessary to reduce the dye to a soluble leuco sodium salt under strong reducing agent and alkaline conditions to dye the fiber, and then oxidize the leuco dye and then oxidize it. It is converted to the original insoluble dye and fixed to the fiber. At present, indigo is widely used in the coloration of cellulose fabrics, especially cotton denim. After dye reduction and dissolution, leuco-dyeing, leuco oxidation, and post-treatment, it achieves the purpose of dyeing. The style is popular around the world [1-5]. Literature [6-7] reported on the dyeing process of reduced indigo on silk, and found that the alkaline dyeing conditions of reduced indigo will inevitably cause damage to the fiber and affect the quality and style of the final product.
From the molecular structure (Fig. 1), the indigo blue is similar to the reduced indigo structure, and the indigo blue has two more sulfonic acid groups at the 2-position of the benzene ring than the reduced indigo. From the theory of dye chemistry, it can be analyzed that indigo blue should be an acid dye, which can be dyed with ionic bonds. In addition, the sulfonic acid group is a special chromophore, and its presence only increases the water solubility of the dye, and the chromophore No significant impact. Therefore, it is theoretically possible to dye wool fibers with indigo blue and to dye the effect of reducing indigo. So, can indigo pigment be used for the dyeing of silk fabrics and dyed to reduce the effect of indigo? In this study, silk fabrics were dyed with indigo disulphonate, often called indigo blue in the food industry, to explore the optimum process conditions for dyeing, in order to utilize the special physical and chemical properties of silk and indigo, and to continue the world on silk fabrics. The desire for love and the love of cowboys.
1 ·Test 1.1 Test materials and instruments Test materials: scouring silk fabric, 150 g/m2 cotton bleached cloth, indigo blue (Zhuhai Jintian Natural Pigment Co., Ltd.), reduction indigo (Guangdong Qiyun Biotechnology Co., Ltd.), fixing Agent WS (Yancheng Meifeng Auxiliary Co., Ltd.), sulfuric acid, sodium sulfate, caustic soda, insurance powder (analytical grade, Tianjin Yongda Chemical Reagent Co., Ltd.).
Test equipment: YP102N electronic balance (Shanghai Tianping Instrument Factory), 721 photoelectric spectrophotometer (Shanghai Tianmei Scientific Instrument Co., Ltd.), Datacolor 600 spectrophotometer (Switzerland Datacolor), HH-S constant temperature water bath, SW-12A Type wash fastness tester, Y571B type rubbing fastness tester (Nantong Sansi Company).
1.2 Test method Indigo blue pigment concentration 0.4 g / L, bath ratio 1: 50, adjust the pH value of 2 ~ 7, add 0 ~ 20 g / L of salt, 40 ° C into the dyeing, warming to a certain temperature, dyeing for a certain time to take out, Washed.
1.3 Test methods 1.3.1 Color parameters The color parameters a, b, h, K/S were measured on the dyed fabric using a Datacolor 600 spectrophotometer. Where a is the red and green direction color parameter, b is the yellow and blue direction color parameter, h is the hue angle, and K/S is the dyeing depth. The color measurement conditions are D65 light source, 10° field of view.
1.3.2 Rubbing fastness According to GB/T3920-1997 "Color fastness to rubbing of textiles test".
1.3.3 Wash fastness According to GB/T3921.1-1997 "Textile fastness test color fastness: test 1".
1.3.4 Dyeing rate (E)
The residual liquid colorimetric method was used to determine the absorbance of the dye solution on a 72l photoelectric spectrophotometer, using a l cm cuvette, and E was calculated according to formula (1):
In formula (1): A0 and A1 are the absorbances of the dye liquor before and after dyeing, respectively.
1.3.5 Levelness
2. Results and discussion 2.1 The dyeing performance of indigo blue pigment 2.1.1 The effect of pH value of dyeing bath on dyeing depth is 0.4 g/L in indigo pigment, bath ratio 1:50, salt 20 g/L, dyeing temperature 80 °C For the dyeing of silk fabrics for 60 min, the effect of dyeing bath pH on the dyeing depth is shown in Fig. 2. It can be seen from Fig. 2 that when the pH of the dyeing bath is less than 6, the dyeing depth is not much different under each acidic condition. When the pH value is greater than 6, the dyeing depth decreases significantly. Because silk fibroin has poorer stability to acid than wool, when dyeing under strong acidic conditions, the luster, feel and strength of silk are affected, so it is more reasonable to set the dyeing pH to 6. In addition, the isoelectric point of silk fibroin has a pH of 3.5 to 5.2. At this time, the form of the dye molecule and the silk is van der Waals force, hydrogen bond, and ionic bond.
2.1.2 Effect of dyeing temperature on dyeing depth Silk fabric was dyed at a mass concentration of 0.4 g/L, a bath ratio of 1:50, a salt of 20 g/L, a pH of 6 and a dyeing time of 60 min. The effect on the depth of dyeing is shown in Figure 3.
As can be seen from Figure 3, the depth of dyeing increases as the dyeing temperature increases. As the temperature increases, the degree of aggregation of the dye in the dye liquor decreases, and at the same time, the degree of expansion of the fiber increases, and the rate at which the dye adsorbs and diffuses into the fiber is accelerated. Because silk fabrics are generally light and thin, the gloss is required to be high, and the surface is easily scratched. If the fabric is boiled for a long time, the fabrics rub against each other, which may cause partial "grey damage". Therefore, it is not easy to select boiling dyeing. Considering that the dyeing depth increases slowly after 80 °C, the effect of temperature on the dyeing depth is not obvious, so the dyeing temperature is chosen to be 80 °C.
2.1.3 Effect of dyeing time on dyeing depth Silk fabric was dyed and dyed at an indigo pigment concentration of 0.4 g/L, a bath ratio of 1:50, a salt of 20 g/L, a pH of 6, and a dyeing temperature of 80 °C. The effect of time on dyeing depth is shown in Figure 4. It can be seen from Fig. 4 that the dyeing depth tends to increase with time, and the time is too long to affect the hand and strength of the silk. Finally, the dyeing time was set to 60 min.
2.1.4 Effect of electrolyte concentration of sodium sulphate on dyeing depth In the concentration of indigo blue pigment concentration 0.4 g / L, bath ratio 1:50, pH 6, dyeing temperature 80 ° C, dyeing time 60 min, the concentration of electrolyte sodium sulfate mass concentration The effect of depth is shown in Figure 5. It can be seen from Fig. 5 that sodium sulfate has a dye-sensing effect on the dyeing process, and the dyeing depth increases with the increase of the mass concentration of sodium sulfate, and the rate is fast and slow first. After reaching 15 g/L, the effect is not obvious. The isoelectric point of silk fibroin has a pH of 3.5 to 5.2 and a dyeing pH of 6. Above the isoelectric point, the silk and the dye molecules have the same charge. The electrolyte can be added to the negative charge on the fiber and the dye in the dyebath. The negative charge brought about by the shielding function greatly reduces the obstacle of dyeing the dye on the dye and promotes the dyeing effect. When the mass concentration of electrolyte sodium sulfate reached 15 g/L, the increase of the dyeing effect was not obvious.
In summary, in the case of a dye concentration of 0.4 g / L, the dyeing conditions of the indigo blue silk fabric are pH 6, the concentration of electrolyte sodium sulfate is 15 g / L, the dyeing temperature is 80 ° C, and the dyeing time is 60 min.
2.2 Dyeing effect The color parameters a, b, and h were tested on the silk fabric dyed with indigo blue and the cotton fabric dyed with reduced indigo. The results are shown in Table 1. It can be seen from the data in Table 1 that, compared with the reduced indigo dyeing, the yellow-blue color parameter b is not much different after the indigo dyeing, the red-green color parameter a is different, and the indigo dyeing effect is more green than the reduced indigo; The indigo blue phase angle h is slightly smaller than the reduced indigo blue, but both are in the blue range, and the indigo blue is close to the reduced indigo blue, slightly greenish.
It can be seen from the data in Table 2 that after dyeing the silk fabric, the indigo pigment has poor fastness, especially the wet processing fastness, and the aldehyde-free fixing agent WS is used for the preliminary fixing test to improve the color fastness. After the modified dyeing, the fabric was treated in a 2% fixing solution at a bath ratio of 1:50 and 40 °C for 10 min, and washed with water to test the color fastness. After fixing treatment, the dyeing fastness can be improved by 0.5 to 1 level, which basically meets the requirements for taking. Indigo pigment has high dyeing rate on silk fabric, high dye utilization rate in dyeing process, and good dyeability after dyeing under the preferred process conditions, S(λ) is 0.07.
3· Conclusions 1) In the case of dye concentration of 0.4 g/L, the dyeing conditions of indigo blue on silk fabric are: pH6, electrolyte sodium sulfate 15 g/L, dyeing temperature 80 °C, dyeing time 60 min.
2) According to the special physical and chemical properties of silk and indigo, the hue after dyeing with indigo blue is similar to the traditional reduced indigo blue, which realizes the indigo effect after dyeing silk fabric.
3) After dyeing under the optimal process conditions and after simple fixing treatment, the dyeing dyeing rate, leveling property and color fastness of the silk fabric are all processed and taken.
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