After treatment of Direct Dyed Goods -
The reasons for the popularity of direct dyes within the dyeing of cellulosic fibres are the low cost of dyeing and also the easy dyeing procedure.
These dyes don't possess adequate washing fastness properties and most of them fade in the light.
The use of direct dyes, therefore, becomes undesirable for material which can subsequently be washed frequently or continuously exposed to light.
(A) Increasing mass of fabric
(B) Decreasing solubility of water after dyeing
Several methods have been devised to spice up the fastness properties of Direct dyes.
This after-treatment are supported by principles like increasing the mass of dye and thus decreasing their solubility in water dyeing.
All the direct dyes, however, are not capable of such after treatment since in many cases, the colour of the last word product changes i.e it tends to become duller and sometimes the hue is altered.
Some after-treatments that are in use are summarised below:
(a) Treatment with copper Salts
(b) Treatment with chromium compounds
(2) Treatment with formaldehyde
(3) Treatment with cationic dye fixing agents
(4) Topping with basic dyes
(5) Diazotization
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| After treatment of Direct Dyed Goods |
Explanation -
(1) Treatment with metallic salts -
(a) Treatment with copper Salts -
Certain dyestuffs are capable of reaching copper and showing remarkable improvement in light-fastness properties. The dyed material is treated in a bath containing:
Recipe | Quantity |
Copper sulphate (owf) | 0.5 to 2% owf |
Acetic acid (30%) (owf) | 0.5 to 2% of |
(Note - of - on the weight of fabric )
The exact chemical concentration depends on the intensity of the colouring. The procedure lasts 30 to 40 minutes at 80°C. After that, the fabric is rinsed and dried. rather than the aforementioned chemicals, commercial products like Cuperantine, Cuprofix, and Cuprophenyl have also been employed.
(b) Treatment with chromium -
Certain direct dyes can have chromium atoms added to their molecular structure, creating a more complex structure than those with copper compounds. This increases the dyes' washing fastness properties. However, this procedure leaves their light-fastness characteristics unaffected.The coloured items were treated in an exceeding bath that contained:
Recipe | Quantity |
Potassium dichromate | 2 to 3% (owf) |
Acetic acid | 2 to 5% (owf) |
(Note - of mean on the weight of fabric)
The treatment lasts at a boil for 30 minutes. After that, the products are dried and rinsed.
Improved washing and light fastness qualities can be obtained by combining the treatment with copper and chromium compounds.
The items are worked with in a bath that contains the following ingredients:
Recipe | Quantity |
Potassium dichromate | 0.5 to 2,%(owf) |
Copper sulphate | 0.5 to 2%(owf) |
Acetic acid | 1 to 5 %(owf) |
The treatment is for 30 minutes at 80°C followed by rinsing and drying.
(2) Treatment with formaldehyde -
Some direct dyes can also be treated with formaldehyde to increase the relative size of the dye molecules, improving the dyes' washing fastness qualities.
The treated items are put in a bath with:
Recipe | Quantity |
Formaldehyde (40%) | 2 to 3% |
Acetic acid | 1% |
The treatment is carried out at 60 to 70°C for 30 minutes followed by rinsing and drying.
(3) Treatment with cationic dye fixing agents -
To enhance the washing fastness features of Direct Dyes products, a range of dye-fixing agents are available; nevertheless, the sunshine fastness is compromised.These substances have the power to ionise into small anions and lengthy cations. Direct dyes, on the opposite hand, ionise into long anions and short cations.
Consequently, larger complexes emerge when the solutions of those two are combined.
The wet fastness of the coloured material is improved since the complex's mobility is significantly reduced.
The dyed items are treated for a half-hour at the recommended temperature (which varies for various products) with 1 to 2 per cent (of) cationic dye fixing agents, so rinsed and dried.
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| After treatment of Direct Dyed Goods |
Questions -
- Which two principles are used after the treatment of Direct Dyed Goods?
- Describe treatment with metallic salts of direct dyes.
- Describe treatment with formaldehyde of direct dyes.
- Describe treatment with cationic dye fixing agents of direct dyes.
References
Chakrabarti, R., & Mehta, N. (2008, November 8). Quick Level Dyeing of Direct Dyes. Fibre2fashion.com; Fibre2Fashion. https://www.fibre2fashion.com/industry-article/3742/quick-and-level-dyeing-of-direct-dyes-dyrite-process
Clark, M. (2011). Handbook of textile and industrial dyeing: Principles, processes and types of dyes (Matthew Clark, Ed.). Woodhead Publishing.
Hasin, S. (2020, July 16). All about direct dyes. Textile Property. https://www.textileproperty.com/direct-dyes/
Sayed, A. (n.d.). Direct dye: An overview [A to Z]. Blogspot.com. from https://textileapex.blogspot.com/2015/01/direct-dye.html
The Editors of Encyclopedia Britannica. (1998). direct dye. In Encyclopedia Britannica.
Trivedi, Y. (2020, November 18). Dyeing of cotton fabric with direct dyes. Textilesphere.com. https://www.textilesphere.com/2020/11/dyeing-of-cotton-with-direct-dyes.html
Further read,
Writer - Rushikesh Patil (Textile Engineer)
