Application of direct dyes -
In machines that may operate at atmospheric pressure, direct dyes are often added with electrolytes at or near the boil. |
| Direct dyed fabric |
Different cellulosic materials are dyed using direct dyes. they'll be dyed within the varieties of fibre, yarn, textiles, and clothing. they'll be utilized in the subsequent procedures:
(a) Exhaust process
(b) Semi-continuous process
(c) Continuous process
With acid-sensitive direct dyes and H2O, the addition of alkali, often salt, could also be made to boost the dye solubilization.
When cellulose is submerged during a dyestuff solution, the dye is absorbed until equilibrium is reached, at which point the bulk of the dye is absorbed by the fibre.
Each dye encompasses a different rate of equilibrium depletion and absorption. the quantity of dye absorbed by the fibre about the quantity still within the dyebath is understood because of the substantivity of the dye for cellulose.
The dyeing process involves two steps:
(ii) Dyeing
Explanation-
Preparation of the dye bath -
By pasting the dye with a small amount of water and sodium carbonate, the dye is countermined.
The paste should then be continuously stirred while boiling water is added.
If pasting isn't done before adding boiling water, the dye may bulk up, which can cause dyeing to be speckled.
Typically, stock solutions (also referred to as concentrated solutions) are made, and therefore the necessary amount of those solutions is then used for dyeing.
Typical Dye Bath formulation -
Recipe | Quantity |
Dyestuff (direct dyes) | X% |
Soda ash | Up to an equal weight of the dye |
Common salt | Light shade 5% |
Medium shade 10% | |
Dark shade 20%(owf) | |
Temperature | Boil |
Time | 45 to 60 minutes |
.jpeg "Direct dyed fabric") |
| Dye bath machine |
Process-
(2) the water should be adjusted to the MLR of various fabrics;
(3) well-prepared fabric, or (RFD) ready for dyeing fabric, should be taken and immersed in the dye bath;
(4) temperature rises slowly to boiling;
(6) add salt in two instalments.
(7) dyeing at a boil for 45 to 60 minutes; and
(8) after dyeing, the fabric should be dried.
Process sequence -
Dyeing > Washing > After-treatment
Dye bath variables must be considered for level dyeing. -
(2) Electrolyte concentration and addition
(3) Time
(4) Dye solubility
(5) Use of levelling agent
 |
| Drying of dyed fabric |
Questions -
- Which applications of direct dyes are useful?
- Describe the preparation of the dye bath.
- What is the process for dye bath preparation?
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,
Part 2 Mechanism and effects of Dyeing
Part 3 Application of direct dyes
Part 4 Direct dyes for certain fibres
Part 5 After treatment of Direct Dyed Goods
Part 6 Other treatment of direct dyed goods and stripping
Writer - Rushikesh Patil (Textile Engineer)
