Wetting Agent:
Reduces surface tension
Increases wettability of the fabric
Increases dye penetration
Sequestering Agent
Reduces water hardness
Deactivates Metal ion
Example: EDTA ( Ethylene diamine tetra acetic acid )
Levelling Agent
Slows down dye uptake of fiber
Helps to produce more uniform color
Levelling agents for dyeing are often surfactants that are said to be either fibre substantive or dye substantive.
These are often used to control the rate of dyeing of wool and nylon in weakly acidic solution.
Their small molecular size allows rapid penetration into these fibres and interaction with the ammonium ion groups therein. This slows down dye absorption.
When acting in this manner, these auxiliary chemicals are often called blocking agents.
Cationic dyes often have a very high initial rate of adsorption on the fibre surface above a critical temperature, which can lead to unlevel dyeing.
Cationic surfactants of low substantivity initially block a considerable number of the anionic sites in the fibre and allow a more gradual uptake of dye, leading to a uniform dyeing.
Dye-substantive levelling agents prevent dye absorption by the fibre by complex formation with the dye in the dye bath. This complex is of such a molecular size that it cannot penetrate into the fibre. As the dyeing temperature gradually increases, the complex becomes less and less stable and the dye is gradually liberated and free to enter the fibres.
Binder
Works as an adhesive to attach pigment with fiber
Carrier
Swells the fiber
Used in hydrophobic fiber
The usual effect of the carrier is to increase both the rate of dyeing and the dye-bath exhaustion
A carrier is an organic compound, dissolved or emulsified in the dyebath, which increases the rate of dyeing.
Carriers allow dyeing of even deep shades at the boil within a reasonable dyeing time.
The polyester fibres absorb the carrier and swell.
This speeds up the diffusion of the dye into the fibres.
Alternatively, the carrier may form a liquid film around the surface of the fibre in which the dye is very soluble, thus increasing the rate of transfer into the fibre.
Carriers are also useful for dyeing wool/polyester blends when there is a risk of damaging the wool at dyeing temperatures above 100 °C. In this case, the carrier also helps to prevent cross-staining of the wool by the disperse dye.
Example: polyester dyeing carriers > butyl benzoate, methyl naphthalene, di-chloro-benzene, diphenyl and o-phenyl-phenol.
Dispersing Agent
Disperse dyes are available as powders, grains, pastes or aqueous dispersions. These all contain micro-fine dye particles, many with diameters below 1 um. Liquid disperse dyes are useful for continuous dyeing. Settling and aggregation of dye particles in pastes and liquids can lead to coloured specks on the dyed fabric.
Dispersing agents coat the surface of dye particles with a layer of adsorbed dispersant.
Dispersing agents are anionic polymers. So they are adsorbed into the hydrophobic dye particle chain with exposing an anoininc group to the surrounding water. So the overall negative charge on the surface of each particle prevents their coalescence and aggregation.
The presence of a dispersing agent in the dye bath increases the apparent water solubility of the dye
Decreases the dyeing exhaustion.
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