A Brief Discussion on Function of Dispersing Agent!

Dispersant or dispersing agent makes the dispersion process more stable and easier of solid material dispersed in liquid.

Dispersing agent has an effect on the rate of dyeing. It increases the solubility of disperse dye as well as increases the dyeing rate up to a certain time. But after that certain value, the rate of dyeing decreases with the addition of disperse dye.

Dispersing agents are stable under dyeing conditions. They are significantly resistant to hard water, high temperature even at the other dyeing auxiliaries.

They help to maintain the dye molecule dispersion in dye bath. Disperse dyes remain at aggregated form which is not suitable for the application on hydrophobic fibers.

If they remain at aggregated form, they will produce uneven and specky shades. So dispersing agent is required to produce stable formulation and to ensure storage stability (No viscosity instability, no separation).

It helps to distribute the solid dye particles in the liquid solution.

Function of dispersing agent:

• It helps to reduce the particle size of dye
• Enables the formation of dye powder form
• For carrying out dyeing, it helps in the re-conversion process of dye powder into a dispersion
• Maintains the dispersion of dye in fine form during the whole dyeing process
• Having no wetting, foaming or detergent properties
• Increases the solubility of Disperse dye
• It has an impact on the rate of dyeing
• Shows compatibility with anionic and non-ionic products

Effect of dispersing agent on rate of dyeing

• Ii is seen from the above figure that the dyeing rate increases with increasing solubility up to a certain value and with further increase in solubility, the dyeing rate actually decreases. Where the solubility is very high as in case of direct dyes, practically no dyeing takes place.
• If the dye has fairly low solubility, say OA, the addition of a dispersing agent raises the solubility to OB so that the dyeing rate increases from AP to BQ.
• If the dye has fairly high solubility (OB), the addition of the dispersing agent may increase it further, say to OD. In this case, the dyeing rate is actually decreased from BQ to DS.

Trade names of dispersing agent

Examples of dispersing agents:

• Soap powder
• Lignin sulphonates
• Turkey red oil
• Formaldehyde
• Alkyl acryl sulphonates

Dispersing agent plays an important role in dyeing of polyester with disperse dye. It helps in dyeing by increasing the solubility of disperse dye along with an increase in the dyeing rate up to a certain time.