Extraction And Stripping Processes of Commonly Used Dyes

principle：

Pulling color, also known as stripping color, is generally achieved by using chemical reactions to break the binding of dyes on fibers and the structure of dyes on fibers, resulting in the detachment of dyes from fibers and the inability to produce color.

There are mainly two types of commonly used colorants: reducing colorants and oxidizing colorants.

Restoration and color removal agents: Commonly used ones include insurance powder and carving white powder. They achieve the purpose of fading and fading by disrupting the chromophore system in the dye molecule structure. Dyes with azo structures can have their azo groups reduced to amino groups and cannot produce color. However, the damage caused by reducing agents to certain structural dye coloring systems is reversible, such as the anthraquinone structure coloring system, so its fading is recoverable.

Oxidation color remover: Commonly used are hydrogen peroxide and sodium hypochlorite. Under certain conditions, oxidants can destroy certain functional groups that make up the chromophore system of dye molecules, such as decomposing azo groups, oxidizing amino groups, hydroxymethylation, and dissociating complex metal ions. These irreversible structural changes can cause dyes to fade and fade, so theoretically, oxidative color removers can achieve complete color removers. The use of such color removers for anthraquinone structured dyes is particularly effective.

The color extraction process of different dyes

1. Color extraction of reactive dyes

Light color: Under alkaline conditions, the color of the insurance powder is extracted, such as 2g/L caustic soda and 4g/L insurance powder at 95 ℃ for 30 minutes, followed by hot washing and then water washing

Dark color: restored color extraction+oxygen bleaching, such as: caustic soda 4g/L+sodium hydrosulfite 8g/L 95 ℃ 40min → hot washing → oxygen bleaching → hot washing → water washing

2. Color extraction of sulfide dyes

The correction of fabrics dyed with sulfur dyes usually involves first placing them in a reducing agent blank solution (6g/L full strength sodium sulfide) and treating them at the highest possible temperature to partially remove the color from the dyed fabric before re dyeing. In severe cases, sodium hypochlorite or sodium hydrosulfite should be used.

Light colored fabric color extraction process:

Color defect cloth → multiple immersion and rolling (sodium hypochlorite 5-6g/L, 50 ℃) → 703 steamer (2 minutes) → thorough water washing → drying

Dark fabric color extraction process:

Color defect cloth → Rolling oxalic acid (15g/L, 40 ℃) → Drying → Rolling sodium hypochlorite (6g/L, 30 ℃ × 15s) → Thoroughly washing with water → Drying

Intermittent color extraction process:

55% crystalline sodium sulfide 5-10g/L; Soda ash 2-5g/L (or 36 ° Be NaOH 2-5ml/L); Temperature range of 80-100 ℃; Time 15-30 minutes; Bath ratio 1:30-40.

3. Color extraction of acidic dyes

Boil with ammonia water (20-30 g/L) and anionic wetting agent (1-2 g/L) for 30-45 minutes. Before processing, use insurance powder (10-20g/L) to treat at 70 ℃, which is beneficial for complete color extraction. Oxidation color extraction method can also be used.

Under acidic conditions, the addition of special surfactants can have a good color extraction effect, and alkaline conditions can also be used for color extraction.

True silk coloring process:

Reduction stripping bleaching (1g/L pure alkali, 2g/L flat added O, 2-3g/L sodium hydrosulfite, 60 ℃, 30-45min, bath ratio 1:30) → Pre media treatment (FeSO4, 7H2O 10g/L, 50% hypophosphite 2g/L, formic acid adjusted pH=3-3, 5, 80 ℃ × 60min) → Rinse (80 ℃ × 20min) → Oxidation stripping bleaching (10mL/L 35% hydrogen peroxide, 3-5g/L NaSiO3.5H2O, 70-80 ℃, 45-90min, pH=8-10) → Cleaning

Wool coloring process;

Nifedipine AN4%; Oxalic acid 2%; Heat up to boiling point within 30 minutes, maintain for 20-30 minutes, and then clean.

Nylon color extraction process:

36°NaOH 1%～3%； Pingpingjia O 15% to 20%; Synthetic detergent 5% to 8%; Bath ratio 1:25-30; 98～100℃； 20-30 minutes (until complete decolorization). After complete decolorization, gradually cool down, wash thoroughly with water, then treat with 0.5ml/L acetic acid at 30 ℃ for 10 minutes to fully neutralize the alkali remaining on the nylon, and then wash with water.

4. Color extraction of vat dyes

Generally, in a mixed system of sodium hydroxide and sodium hydrosulfite, dyes on fabrics are re reduced at higher temperatures, sometimes requiring the addition of polyvinylpyrrolidone solution, such as BASF's ALigen A

Continuous color extraction process:

Color defect cloth immersion rolling reduction solution (caustic soda 20g/L, insurance powder 30g/L) → 703 reduction steaming box steaming (100 ℃) → water washing → drying

Intermittent color extraction process:

Add O 2-4 g/L at a flat level; 36°NaOH 12～15mL/L； Insurance powder 5-6g/L; 70～80℃； 30～60min； Bath ratio 1:30-40.

5. Color extraction of dispersed dyes

The color extraction methods for dispersing dyes on polyester fibers include:

⑴ Treat with carved white powder and carrier at 100 ℃ and pH 4-5. If treated at 130 ℃, the effect is more significant.

Treat with sodium chlorite and formic acid at 100 ℃ and pH 3.5.

To achieve the best results, the best method is to apply the ⑴ treatment followed by the ⑵ treatment, and then dye black as much as possible after treatment.

6:Color extraction of cationic dyes:

There are usually the following methods for cationic dye extraction on acrylic fiber:

Boil for 1 hour in a treatment bath containing 5ml/L monoethanolamine and 5g/L sodium chloride; After cleaning, bleach for 30 minutes in a treatment bath containing 5ml/L sodium hypochlorite (150g/L effective chlorine), 5g/L sodium nitrate (corrosion inhibitor), pH 4-4, and 5; Finally, treat with sodium sulfite (3g/L) at 60 ℃ for 15 minutes or with 1-1.5g/L sodium hydrosulfite at 85 ℃ for 20-30 minutes, and clean thoroughly.

Using a detergent (0, 5-1g/L) and a boiling solution of acetic acid to treat dyed fabrics at a pH of 4 for 1-2 hours can also achieve partial color removal.

Color extraction of 7 insoluble azo dyes

Treat with 5-10mi/L 38 ° caustic soda, 1-2ml/L thermal stability dispersant, and 3-5g/L sodium hydroxide powder, and add 0-1g/L anthraquinone powder as indicators. If there is enough insurance powder and caustic soda, anthraquinone will turn the stripping solution red; If the stripping solution turns yellow or brown, further caustic soda and sodium hydrosulfite must be added. The fabric after color extraction should be thoroughly cleaned.

8 :Stripping of paint

The coating is difficult to peel off, and generally only potassium permanganate can be used for shallow peeling.

Process: Color defect cloth → Rolling potassium permanganate (18g/L) → Water washing → Rolling oxalic acid (20g/L, 40 ℃) → Water washing and drying

be careful:

1. Before pulling or correcting the color of the fabric, a sample test must be conducted.

2. After fabric color extraction, it must be washed with water (cold, hot water)

3. The color extraction should be short-term, and if necessary, it can be repeated multiple times.

4. When pulling out colors, it is necessary to strictly control the temperature, amount of additives, and other conditions based on the characteristics of the dye itself, such as oxidation resistance, alkali resistance, chlorine bleaching resistance, etc., to prevent excessive additives or improper temperature control from causing excessive pulling or peeling. If necessary, the process can be determined by layout.

If you want to know more about dyeing solutions, please contact: info@tiankunchemical.com