Why can’t cotton reactive dyeing reach depth? The problem is here~

After the textile is bleached with hydrogen peroxide, the residual peroxide Hydrogen will harm reactive dye dyeing and easily cause color differences, color blooms and other dyeing defects. Ther...

After the textile is bleached with hydrogen peroxide, the residual peroxide Hydrogen will harm reactive dye dyeing and easily cause color differences, color blooms and other dyeing defects. Therefore, H202 must be removed from the fabric and water bath before dyeing.


Cotton knitting pre-treatment

Pure cotton knitted gray fabric or yarn, usually with There are many cotton fiber companions (such as waxy substances, pectin substances, ash, etc.). These companions greatly affect the wettability and dyeability of cotton fibers, so they must be removed through scouring and bleaching before dyeing. Because the warp yarns of knitted fabrics are not sized and the texture specifications are soft, the gray fabrics are usually bleached in a dyeing machine, and then washed, neutralized, and then dyed with reactive dyes. When pure cotton woven fabrics are dyed with bright and medium-light colors, the whiteness of the semi-finished products is often insufficient due to insufficient whiteness. They are subjected to a reoxygenation and bleaching process before dyeing, and are then dyed with reactive dyes after being washed.

Use the oxidation of hydrogen peroxide to remove impurities, pigments, etc. in textiles After the material oxidizes and fades, the textiles have a certain whiteness and hygroscopic properties, ensuring that subsequent dyeing and finishing processes can proceed smoothly. Hydrogen peroxide (also known as hydrogen peroxide) is an indispensable chemical additive in textile pretreatment. Its oxidizing properties and cost advantages make its dosage always occupy the forefront of textile oxidants; hydrogen peroxide is mainly used in the bleaching process. Before dyeing cotton products after scouring and bleaching, if there is residual hydrogen peroxide on the cloth surface and water bath, it will destroy the reactive dye groups and prevent the formation of effective covalent bonds between the dye and cotton fibers, resulting in light colors, blooming, etc. Dye defects.

In actual production, cotton fabrics are oxygen bleached and washed before dyeing In the process mode of dyeing with reactive dyes, there are often problems such as poor color stability (shade, light), poor reproducibility, inaccurate enlargement of small samples, obvious color differences between tanks, and uneven color (color flowers). ; There is also the problem of slow fading (fading) of materials dyed with reactive dyes during the washing process.


Hydrogen peroxide and the impact of residues on active staining

Reactive dyes have poor stability against H202. Various types of reactive dyes have poor stability against H202 in exhaust dyeing. Once there are H202 bands in the reactive dye bath of cotton fabrics If it enters, the reactive groups of the dye will be destroyed, whether it is a low-temperature or high-temperature reactive dye, a medium-temperature or a thermosetting dye.Type reactive dyes, when dyed in a dye bath containing H202, the color depth and color brightness will be significantly reduced, but the degree of decrease is different.

Moreover, the higher the H202 content, the greater the decline; in severe cases, it will cause color difference, color flowers and colors. Therefore, the residual hydrogen peroxide on the fabric and the H202 in the water bath must be removed before dyeing. Otherwise, the residual hydrogen peroxide will oxidize and fade the dye, resulting in dyeing defects such as low color yield and color bloom on the textiles.

There are two reasons

(1) The chromophores or active groups of some dyes are destroyed by H202, causing the dyes to become decolorized or lose their dyeing ability.

(2)The bond between the dye and cellulose is broken, causing the dyed dye to fall off (generally speaking, the stronger the chemical activity of the active group, the easier it is for the dye-fiber bond to break).

Therefore, only when hydrogen peroxide is brought into the dye liquor (even if the concentration is very low), obvious color lightening will occur. This can be confirmed from the following experiments, see Table 1 below.

Table 1 Effect of hydrogen peroxide on conventional reactive dye dyeing results

In the dye bath containing H202, various types of reactive dyes and cellulose fibers have formed The binding bonds will also produce a certain degree of “bond breaking” phenomenon; this shows that the impact of H202 on the dyeing results of reactive dyes (color reduction, discoloration) is mainly caused by the destruction of the chromogenic group or active group of the dye. .

(1) Reactive dyes have poor stability against H202 and should be dyed before dyeing Oxygen bleaching, washing with water and then dyeing with reactive dyes can easily lead to color instability. This is because after the fabric is rope-shaped oxygen bleached in a jet overflow dyeing machine or an airflow dyeing machine, the H202 contained in the fabric is usually difficult to clean thoroughly. Once it is brought into the subsequent dye bath, it will inevitably cause color (shade, light) changes. fluctuation.

(2) Oxidative “bond break” existing in the bond between reactive dyes and cellulose fibers This phenomenon is the reason why the dyed materials with reactive dyes will gradually fade during the washing process. This is because commonly used household detergents generally contain oxides such as sodium perborate and sodium percarbonate, which can catalyze the breakage of the bonds between reactive dyes and cellulose fibers to varying degrees.

No residual hydrogen peroxide in the dye bath 5 mg/L H202 content in the bath 30 mg/L H202 content in the bath

The residual amount of hydrogen peroxide in the dye bath is generally detected by test paper.


Introduction to oxygen removal and cleaning process

The oxygen removal and cleaning processes to eliminate the negative impact of H202 on the dyeing results of reactive dyes include: water washing and oxygen removal, reducing agent treatment and enzyme treatment.

1. Washing and deoxidation method

A. By-rinsing washing

Washing to remove oxygen, that is, use a large amount of water to remove the remaining residue on the cloth Rinse with hydrogen peroxide, dilute and remove.

Process flow: Bleaching→Rinsing (washing) → Rinsing (washing) → Rinsing (washing) → Rinsing (washing) → Dyeing (dying).

After bleaching or oxygen bleaching before dyeing, use hot water washing → hot water washing → overflow cold water washing. Only after confirming that the H202 has been fully washed out can you start dyeing with reactive dyes. This method consumes a lot of energy, emits a lot of pollutants, is costly and difficult to remove, and is obviously not in line with today’s dyeing and finishing concepts of “energy saving, emission reduction, and efficiency improvement”.

B. With reducing agent reducing agent cleaning

Reducing agents generally use sodium hyposulfite (sodium thiosulfate), insurance Powder (sodium dithionite), etc. is used as a reducing agent, reacts with hydrogen peroxide, and is subsequently washed with water to remove the remaining reducing agent.

Process flow: Bleaching→Rinsing (washing) → Reducing agent (reducing agent) → Rinsing (washing) → Dyeing (dying).

Water washing and deoxygenation may cause the risk of incomplete deoxygenation.�; Reducing agent deoxygenation may also cause the problem of incomplete cleaning of reducing agent substances, which affects the dyeing performance; and compared with enzyme treatment, the water washing deoxidation and reducing agent deoxygenation processes are long and consume a lot of water.

C. With Catalase deoxygenase deoxygenation

Enzyme treatment refers to the use of catalase to catalyze the decomposition of hydrogen peroxide to achieve the purpose of oxygen removal , enzyme treatment has the advantages of rapidity and thoroughness.

Process flow: Bleaching→Rinsing (washing) → Catalase (catalase) → Dyeing (dying).

Different oxygen removal methods correspond to reactive dyeing effects:

A. Deoxygenase removes oxygen B. Reducing agent to remove oxygen C. Water washing to remove oxygen

Wash to remove oxygen, that is, wash repeatedly with cold water, so that Not only does it consume too much water, electricity, and steam, the process time is too long, and there is a risk of incomplete oxygen removal; the oxygen removal of the reducing agent may also cause the problem of incomplete cleaning of the reducing agent. Moreover, compared with enzymatic treatment, the process of water washing and oxygen removal and reducing agent deoxidation is long and consumes a lot of water. Therefore, the biological enzyme deoxidation method is the fastest and most effective, and has outstanding advantages in energy saving, emission reduction, and efficiency improvement. The emergence of environmentally friendly catalase, a specific biocatalyst, provides an oxygen bleaching biological purification process.

Enzyme treatment to remove oxygen is the best choice to meet the requirements of energy saving and emission reduction and to ensure the quality of textile processing; due to Only one cold water wash is required, and neutralization, deoxygenation and dyeing can be carried out in the same bath; the biological enzyme deoxidation method is the fastest and most effective, and has outstanding advantages in energy saving, emission reduction and efficiency increase; this new green process has outstanding “energy saving, emission reduction, efficiency” advantage.

2. Biological deoxygenation enzyme deoxygenation method

Mainly used for biological purification after oxygen bleaching, to remove hydrogen peroxide remaining in textiles and their process environment after oxygen bleaching before dyeing; a specific biocatalyst environmentally friendly process The emergence of catalase provides an oxygen bleaching biological purification process; this new green and efficient process can greatly shorten the process time, save water, reduce energy consumption, efficiently and thoroughly decompose hydrogen peroxide, making dyeing completely environmentally friendly.

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