Aftertreatment of direct dyes with diazotization and coupling
After treatment of direct dyes with diazotization and coupling
Hello viewers, hope that you all are well today. Today I come to discuss After treatment of direct dyes with diazotization and the coupling of viscose rayon dyeing with direct dye.
Condition: In which direct dyestuff has Amino group(-NH2) that all are needed to do after treatment by diazotization process.
Process: After dyeing, we need to wash the dyed fabric with normal cold water then we need to do as per the below recipe.
Sodium Nitrite (NaNO2): 1-3% based on the weight of the fabric.
Hydrochloric acid(HCl): 6-7% based on the weight of the fabric.
Temperature: 0-5°C
Time: 15 minutes.
Water: 15 times than fabric weight.
First of all, need to take a pot there need to mix Sodium Nitrite and Hydrochloric acid, and need to keep the temperature at 5°C and mix them up well to increase the fastness quality of the fabric.
After treatment with the cat Ionic fixing agent: This is a surface active cat ionic agent or compound which add to dye anion and make complex molecule and gives good wet fastness quality. These also reduce light fastness. We can complete though below process:
Fixing agent: 1-3% based on the weight of the fabric.
Temperature: 70°C
Time:15-20 minutes
After dyeing with direct dye we need to react with the fixing agent. The recipe percentage depends on the depths of the shade and the thickness of the fabric. Here also used some formic acid and acetic acid. Formic acid and acetic acid help to participate in cationic fabric reactions.
In direct dyeing, there is some helping chemistry:
1. Wetting agent:
a) Helps to absorb dye molecules in the fiber.
b) Reduce surface tension of water.
c) It helps to wet textile materials.
2. NaCl:
a) Increase fiber absorbency
b) Used for deep shade
3. Sodium Sulphate:
a) To produce medium shade it is necessary.
b) It increases the dye's affinity to a textile fiber.
4. Gluber salt:
a) This is known as an electrolyte and is used for producing light shade.
5. Soda Ash :
a) It removes the hardness of water
b) It increases the solubility of the dyes
c)It removes dye and bathes acidity.
d) Increases the working efficiency of salt.
e) Increases the brightness of color fabric.
Stripping of direct dye: The process by which we can remove dye from a colored fabric is known as stripping.
The major objectives of stripping:
a) If the fabric is dyed unevenly then we need to remove the dye from the fabric.
b) Sometimes fabrics can be dyed in deeper shades than required, there also needs to do stripping to reduce shade.
There are two types of stripping processes in the textile dyeing finishing industry.
1. Partial stripping
2. Full stripping
Here is described below :
1. Partial stripping: If the after-treatment process is completed by copper sulfate then we need to use below chemicals :
EDTA: 1-3 grams/liter
Sodium carbonate: 1lb/liter
Need to bring water and chemical temperature in boiling and can complete partial stripping.
In this treatment, copper can be dissolved. If need full stripping is here need to increase the temperature to 90°C in 1-3% EDTA, and the reaction time is 30 minutes. Then reduce the temperature to 80°C and need to add sodium carbonate 3-5 grams/liter and sodium hydroxide 2-3 grams/liter. For this reaction, copper can be dissolved.
2. Full stripping: We need to follow the below recipe to do full stripping:
a) 1-3 % Sodium hydrosulfite
b)Time: 30 minutes
c) Sodium Chloride: 1-2% Based on the weight of the fabrics.
We can boil it in sodium hydrosulfite or we can treat 30 minutes in sodium hydrosulfite and then can wash it off with cold water.
If we want to do full stripping by Sodium hypochlorite bleaching then we can use 0.5-2 grams/liter.
Otherwise, if we want to fully strip sodium chlorite by boiling then we need to control ph with formic acid or acetic acid.
Topping: If we have not gotten the actual shade and the shade is lighter then we need to topping or redyeing the fabric.
