Factors affecting the absorption of direct dye:
The rate of absorption of direct dye depends on the following factors.
1) Effect of pH
2) Effect of temperature
3) Effect of time
4) Effect of electrolytes
5) Effect of concentration
6) Effect of material liquor ratio
Table of Contents
1) Effect of pH:
In most cases, direct dye is applied in a neutral solution (pH = 7). In this case, there is no benefit in adding acid, but there is a possibility of changing the shade. However, alkali has some role in dye absorption, but mild alkali helps to increase the absorption capacity of the dye. 3% soda ash is used to remove water hardness or in some cases to improve solubility. For example, Benz purpurine 4B and chlorazol orange PO, etc. add 3% soda ash to increase the solubility during dyeing. https://bdfabric.com/methods-of-application-of-various-direct-dyes/
2) The absorption of direct dye-Effect of temperature:
Factors affecting the absorption of the direct dye. Different effects In the case of direct dye, maximum exhaustion occurs at different temperatures. Cotton usually has maximum affinity when it reaches the temperature boiling point, but some dyes make cotton the best dye in cold or slightly hot baths in the presence of salt but wool does not show any affinity to direct dyes in cold or slightly hot baths. It shows a strong affinity at boiling temperature. https://bdfabric.com/classification-of-direct-dyes/
3) The absorption of direct dye-Effect of time:
Dyeing will be better if the fabric stays in the dye liqueur for longer than the time required to stay in the dye bath and less dye will penetrate if it is for less than that. If salt or other electrolyte is used to keep the fabric in the dye bath for a long time, the fabric may absorb more dye.
This is because of the molecular size inside the fiber increases and the washing fastness increases. If the amount of dye is less then it takes more time to be absorbed in the same rate. and if the amount of dye is more than it is absorbed in the same rate in less time. In the case of self-leveling dye, if more time is given, even if it is uneven in the past, it still becomes balanced.
4) Effect of electrolytes:
Adding electrolyte to the dye liqueur increases the absorption capacity of the direct dye and in this case, not all types of direct dye use the same electrolyte. Some are not very sensitive to dye salt and some are very sensitive to dye salt.
When cellulosic fibers are immersed in water, a negative charge is obtained. As a result, it tends to repel the negative charge of direct dye. Now if the electrolyte is added to it, it reduces the negative charge of the fiber by interacting with the fiber. This creates hydrogen bonding or Vander wall’s force between the fiber and the dyestuff and the dye enters the fabric.
The more electronegative charge i.e. sulfonic acid group in the dyestuff, the more fiber will be repelled by it. That is, whether or not to add electrolytes depends on the number of sulfonic acid groups in the dye molecule. For example, Crysophenine G has two sulfonic acid groups, so it can dye fibers well without electrolytes. But because Chlorazol FF has four sulfonic acid groups, it cannot dye fibers well without electrolytes.
5) Effect of Concentration:
The higher the density of the dye solution, the more the dye will be absorbed by the fiber. And if the density is low, the absorption will be less. That is, the density is always proportional to the summation. If the density of the dye solution is low, it is a light shade and if the density is high, it is a deep shade.
6) Effect of material liquor ratio:
The ratio of product to liqueur is not the same for all fibers. There are different types of dye liqueur for different fibers. The lower the amount of dye liqueur, the easier it will be to absorb the fiber dye. Product- Liquor ratio depends on the type of product, quantity, and machine used. For example- M: L = 1: (20 – 30) in Open vat for the same cloth, M: L = 1: (6 – 8) in Jigger machine, M: L = 1: (4-5) in pad dyeing machine.
If the amount of liqueur in the product is less, it is called a Short bath. Fiber short baths can absorb more dye and reduce the waste of dyestuff. It has the potential for unequal dyeing. Products If there is more liqueur in the liqueur, it is called a long bath. This will reduce the amount of dye and increase wastage. Considering the economic aspect, short baths are widely used. Because the dye is less wasted.