During the dyeing and finishing production process, dyed varieties often need to be stripped due to various reasons, such as serious color blooms, incorrect shades, etc.
Cotton-span elastic knitted fabrics are mostly dyed with reactive dyes. For light-colored series, stripping is easier and more thorough. However, it is relatively difficult for dark-colored products. The peeling is not complete, there is a lot of residual pigment, the resulting fabric is not white enough, and sometimes the strength loss is too large. In addition, the spandex component contained in cotton and spandex elastic knitted fabrics is relatively sensitive to alkaline conditions, so it is technically difficult to strip dark-colored cotton and spandex elastic fabrics.
This article combines the chemical processing characteristics of spandex fibers in fabrics and uses the insurance powder stripping and hydrogen peroxide bleaching method to study the stripping process of dark spandex knitted fabrics dyed with reactive dyes.
The process flow is: stripping the color of insurance powder, bleaching with hydrogen peroxide, boiling soda, pickling and washing with water.
Strip color
1. Stripping process formula
For dyeing and stripping of dyed fabrics, for cotton-span elastic knitted fabrics, because it contains 3% to 5% spandex fiber, spandex is not resistant to strong The effect of alkali, especially under high temperature conditions, is that strong alkali decomposes spandex. Therefore, the alkali concentration must be reduced as much as possible during the finishing and processing of cotton-span elastic knitted fabrics, and the temperature should not be too high. Using soda ash, the effect on spandex is relatively mild.
Striping process formula
Scouring agent 2%
Soda ash 8%
Insurance powder 8%
2. Stripping process curve
Hydrogen peroxide bleaching
After stripping, the fabric is often not white enough and cannot meet the dyeing requirements. If the light color is re-dyed after stripping, the whiteness of the fabric is required to be higher. Therefore, the dark cotton elastic knitted fabric will have better whiteness after stripping and bleaching it once. Because the fabric contains spandex. Spandex fiber will form nitrogen-chlorine combination in hypochlorite solution, causing fiber damage and yellowing. Polyether type structural damage is more serious (polyester type is 3 to 4 times more chlorine resistant than polyether type). Therefore, chlorine-containing bleach cannot be used for bleaching fabrics containing spandex. Spandex has good stability to oxygen-containing bleach, but the peroxide concentration in the solution should not be too high. In order to reduce damage to spandex fibers, soda ash should be used when bleaching.
Oxygen bleaching process formula
H2O23%
Scouring agent 1%
Na2CO34%
The hydrogen peroxide bleaching process curve is shown in Figure 2
Boiled with soda, pickled, washed
In order to completely remove the residue on the fabric After bleaching with hydrogen peroxide and soda ash, the cotton-span elastic knitted fabric needs to be treated with 2% soda solution at 95°C for 10 minutes, and with 0.5% acetic acid solution at 60°C for 10 minutes, and then washed.
Experiments show that after the dark cotton-span elastic knitted fabric has been treated by the above-mentioned stripping process, because the fabric itself has greater elasticity, and soda ash is used during stripping and bleaching, the effect is relatively Relaxed, the fabric elasticity is not significantly affected. The average values of the 5 measurements of fabric bursting strength and whiteness before and after stripping treatment are shown in the table.
Comparison of whiteness and bursting strength of fabrics before and after stripping treatment
It can be seen from the table that the whiteness of the fabric after stripping treatment is 81%, the strength loss is less than 3%, and the strength loss is small. In addition, the insurance powder stripping and hydrogen peroxide bleaching method has Due to the effect of hydrogen peroxide, the cotton-span elastic knitted fabric will not appear yellowing after decolorization, and the effect is better.
Afterword
The stripping of dyeing in dyeing and finishing factories Re-staining is frequently encountered. Practice has proved that based on the characteristics of spandex fiber, the stripping process of dark-colored cotton-span elastic knitted fabrics dyed with reactive dyes has a good effect. However, after stripping with insurance powder, the moisture and heat resistance of the fabric becomes worse, and the fiber will also suffer a certain degree of brittleness. Therefore, dyeing and finishing technicians need to develop better, efficient and excellent stripping agents and processes. </p
