Acid-reducing cleaning after disperse dyeing
After dyeing polyester fabric with disperse dyes, an acidic cleaning agent is used for reduction cleaning. The application process of the acidic cleaning agent has been optimized. The results show that the color fastness of the fabric after acidic reduction cleaning can reach or even exceed the effect of traditional sodium hydrosulfite reduction cleaning, with less water consumption and a shorter process flow.
When dyeing polyester fabric with disperse dyes, especially for medium and dark shades, a reduction cleaning process is typically required after dyeing to fully remove the loose color and oligomers remaining on the fabric surface and enhance the color fastness. Among various agents, sodium hydrosulfite is widely used for its low cost, effective cleaning, and simple operation. However, sodium hydrosulfite is not entirely safe during application. It is in powder form, flammable, explosive, and prone to decomposition, which can easily release sulfur dioxide gas, polluting the environment and increasing the BOD value of the wastewater, thus making wastewater treatment more challenging. Additionally, polyester fabric is usually dyed under weakly acidic conditions, while sodium hydrosulfite reduction cleaning is conducted under alkaline conditions. Therefore, after dyeing, the liquid needs to be drained, followed by multiple rinses and neutralization with glacial acetic acid after reduction cleaning. This process is cumbersome and water-consuming, necessitating the search for new reduction cleaning agents to replace sodium hydrosulfite.
The acidic reducing cleaning agent is a liquid auxiliary agent specifically developed for acid dyeing of disperse dyes. It can replace sodium hydrosulfite for reducing cleaning of polyester and polyester-cotton fabrics. It features strong reducing ability, good effect in removing floating colors, high safety in application, low dosage, and simple liquid addition. No alkali neutralization is required during use. Light, medium, and dark colors can be directly subjected to reducing cleaning without draining, thus shortening operation time and reducing production costs.
Reduction cleaning process
Conventional alkaline reduction cleaning with sodium hydrosulfite: 2g/L sodium hydrosulfite, 2g/L sodium hydroxide, bath ratio 1:80, 20 minutes. After cleaning, remove the fabric, wash with cold water, and dry.
Acidic reducing cleaner: 2g/L of acidic reducing cleaner, pH=4~5, bath ratio 1:50, temperature 90~95°C, duration 20 minutes. After cleaning, remove the fabric, wash it with cold water, and dry it.
Various fastness tests
Color fastness to rubbing: Tested on a dyeing fastness rubbing tester according to GB/T3920-2008 "Textiles - Tests for Color Fastness - Color Fastness to Rubbing", the O'Moor value is read using a computerized color measurement and matching instrument, and graded according to GB/T251-2008 "Textiles - Tests for Color Fastness - Gray Scale for Assessing Staining".
Color fastness to soaping: Testing is conducted on a washing/dry cleaning color fastness tester according to GB/T3921-2008 "Textiles - Tests for Color Fastness - Color Fastness to Soaping". The Ohm value is read using a computerized color measurement and matching instrument, and the staining grade is evaluated according to GB/T251-2008 "Textiles - Tests for Color Fastness - Gray Scale for Assessing Staining". The fading grade is evaluated according to GB/T250-2008 "Textiles - Tests for Color Fastness - Gray Scale for Assessing Fading".
K/S value: Tested using a computerized color matching instrument
Test conclusion
The acidic reducing cleaning agent exhibits higher reducing property and stability than sodium hydrosulfite. During production and use, it produces no irritating odor, no dust flying, and does not burn when it comes into contact with water. This ensures the health of operating workers and eliminates potential safety hazards in the production workshop, bringing direct economic benefits to users.
Acidic reducing cleaning agent is suitable for reducing cleaning of fibers such as polyester and acetate, as well as their blended textiles (such as wool/polyester, polyester/cotton, polyester/nylon, polyester/cotton/polyurethane, etc.) after disperse dyeing. It can effectively remove unfixed disperse dyes on fibers such as wool, nylon, cotton, and polyester, as well as unadsorbed disperse dyes in the bath, to achieve the desired fastness. The acidic reducing cleaning agent can be effectively applied to blended fabrics of elastic fibers and polyester.
(1) The application process of acidic reducing agent was optimized using orthogonal experimental design. The optimal process is as follows: undrained process, with a cleaning agent dosage of 2g/L, pH=4~4.5, temperature at 90~95 degrees Celsius, and a duration of 20 minutes. The acidic cleaning temperature is slightly higher than that of sodium hydrosulfite cleaning, achieving traditional cleaning results. Additionally, the color fastness to dry rubbing is improved by 0.5 grade, making it a viable alternative to sodium hydrosulfite for reducing cleaning.
(2) The reduction cleaning of polyester fabric after dyeing is safe and environmentally friendly. It can not only fully remove the floating color but also ensure the pH of the fabric surface to be in the neutral or weakly acidic range, thereby reducing the number of water washes. This not only saves energy and water but also shortens the dyeing process.
