Views: 12 Author: Site Editor Publish Time: 2021-12-22 Origin: Site
In the process of dyeing cotton fabrics with reactive dyes, a variety of inorganic salts are used as levelling agents in the dyeing process. Dye the cotton fabrics under different conditions, and determine the best reaction process through comprehensive inspection of the dyeing effect. The results show that sodium citrate has a good dyeing effect under the conditions of 300mmol/L and pH 9 of the dye solution.
Due to its simple molecular structure, bright color, complete chromatogram, simple dyeing process, low cost, and the ability to chemically react with fibers to form strong covalent bonds, reactive dyes have gradually become the main dyes for dyeing cotton fabrics.
Nevertheless, because cotton fiber and dye are both negatively charged in the dye bath, the electrostatic repulsion between the two makes it difficult for the dye to be adsorbed on the fiber, which can easily lead to uneven dyeing; coupled with the hydrolysis of the reactive dye itself and other factors , Resulting in problems such as complex dyeing conditions in the dyeing process, low exhaustion rate and fixation rate, and low dye utilization rate. Among them, the traditional solution is to add inorganic salt in the dyeing process, by adding neutral electrolytes such as inorganic salt to inhibit the ionization of cellulose, thereby reducing the negative electricity of cotton fiber, and reducing the static electricity of anionic dyes during the dyeing process. Repulsion, which makes dyeing easy.
There are many kinds of inorganic salts, and their own properties result in differences in the dye uptake rate and leveling effect during the dyeing process of reactive dyes. Therefore, in this experiment, sodium chloride, sodium sorbate, sodium benzoate, and sodium citrate were used as leveling agents to accelerate the dyeing of cotton fabrics under different inorganic salt concentrations and pH conditions of the dyeing solution. Determine the best dyeing process.
Fabric: Pure cotton knit
Reagents: sodium chloride, sodium sorbate, sodium benzoate, trisodium citrate, soda ash are all AR; reactive blue M-2GE equipment: AL104 electronic balance oscillating dyeing machine, U-3310 ultraviolet-visible spectrophotometer.
A. The influence of different inorganic salts on the dye uptake rate of reactive dyeing
By discussing the influence of different inorganic salts on the dyeing rate of cotton fabrics under the same molar concentration, the optimal inorganic salt that needs to be added in the dyeing process of cotton fabrics is determined, and the dyeing rate of different inorganic salts in the dyeing process is drawn. Curve over time. At the same time, a blank group without inorganic salt was added as a control. Among them, the dyeing process: bath ratio 1:30; dye consumption 2% (owf), inorganic salt concentration 100mmol/L, sodium carbonate concentration 10g/L, dye solution pH neutral, 60℃ for dyeing. By comparing the dyeing effect, the best inorganic salt is screened out.
B. The influence of inorganic salt concentration on the dye uptake rate of reactive dyeing
For further research, we decided to continue to use this inorganic salt after determining an inorganic salt as a leveling agent, and conduct dyeing experiments at different concentrations. By discussing the effect of different molar concentrations of inorganic salt on the dye uptake rate, In order to determine the optimal concentration of inorganic salt.
C. The influence of PH on the dye uptake rate of reactive dyeing
After determining an appropriate concentration of inorganic salt as a leveling agent, adjust the pH value of the dye solution on this basis, and conduct dyeing experiments at different pH to determine the best dye solution pH.
The dye uptake rate of all experimental groups showed a trend of first increasing with the prolongation of the reaction time, and then remained stable after reaching a certain value. Among them, the dye uptake rate increased fastest within 0-10 minutes of dyeing, and then increased slowly; dyeing for 30-40 minutes The post-dyeing rate tends to be balanced. Among them, the experimental group with sodium citrate added had the highest staining rate.
Compared with the control group, the dye uptake rate of the experimental group with the addition of inorganic salt has been greatly improved. This is because the cellulose fiber has more negative charges in the solution, and negatively charged reactive dyes will produce during the dyeing process. Electrostatic repulsion prevents the dye from dyeing the fiber, so the dye uptake and levelness are reduced.
However, after the addition of inorganic salt, on the one hand, the sodium positive ions in the electrolyte can be adsorbed on the surface of the negatively charged fiber. By reducing the negative charge of the fiber, the repulsion between the dye and the fiber is reduced, which is beneficial for the dye to move closer to the fiber. On the other hand, the addition of inorganic salt can increase the ionic strength of the dye liquor and enhance the activity of the dye in the dye liquor, thereby facilitating the diffusion of the dye from the dye liquor into the fiber, reducing the repulsion between the dye and the fiber, and increasing the Dyeing rate. Through comprehensive consideration of dye uptake, sodium citrate should be selected as a leveling agent.
The dye uptake rate of cotton fabric increases with the increase of sodium citrate concentration, but when the sodium citrate concentration reaches 300mmol/L, although the dye uptake rate of cotton fabric increases with the increase of sodium citrate concentration, the overall The change is not too big.
This may be because to a certain extent, as the concentration of sodium citrate increases, the ionic strength of the solution increases, which will accelerate the reaction between dye ions and cellulose ions to a certain extent, but when the electrolyte concentration is too high, But it will cause more dyes to accumulate in the solution and may eventually form precipitates, which in turn further hinders the combination between the dyes and cotton fibers, resulting in the dye uptake rate of cotton fabrics not following the citric acid in the dyeing solution. The increase in sodium concentration increases too much.
Considering that the high concentration of inorganic salt will increase the production cost and it is difficult to degrade, which will cause environmental pollution and other factors. Therefore, under the premise of achieving a better dyeing effect, try to choose a lower concentration of inorganic salt as a leveling agent . Therefore, the concentration of sodium citrate is about 300 mmol/L.
Under different pH values of the dye liquor, the dye uptake rate of the fabric rises rapidly within 0-10min, then slowly increases, and finally reaches a stable value in 30-50min; the dye uptake rate is the value when the dye liquor pH is 9 Highest.
This may be because the pH value has a greater impact on the reaction between dyes and cellulose. Increasing the pH value of the dye liquor increases the concentration of -OH in the dye liquor. Under certain conditions -OH can swell the cotton fiber and make the cotton fabric It can have more space to absorb dye molecules, thereby increasing the dye uptake rate of cotton fabrics; but when the pH exceeds a certain value, the excess -OH in the solution can increase the reaction rate of dyes and cellulose fibers, but At the same time, it will also increase the hydrolysis rate of the dye, which will reduce the dye uptake rate of the cellulose fiber. Therefore, the pH of the dye solution should be set to 9.
1. In the process of dyeing cotton fabrics with reactive dyes, inorganic salts help to improve the dye uptake rate of reactive dyes by reducing the electronegativity of the fiber surface. Under the same conditions, sodium citrate has a better leveling effect.
2. Within a certain range, the dye uptake rate of reactive dyes to cotton fabrics increases with the increase of inorganic salt concentration, but when it reaches a certain concentration, the dye uptake rate does not appear obvious with the increase of inorganic salt concentration. Increase, considering that the high concentration of inorganic salt is not easy to degrade, so under the premise of ensuring the dyeing effect, the concentration of inorganic salt should not be too high.
3. PH value has a great influence on the reaction of dyes and cellulose. Appropriately increasing the pH value of dye liquor can increase the dye uptake rate of cotton fabrics; but when the pH exceeds a certain value, the excess -OH in the solution will increase The rate of hydrolysis of the dye, which leads to a decrease in the dye uptake rate of the cellulose fiber. Therefore, the pH of the dye solution should be weakly alkaline.
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