Dye carriers are organic compounds. They dissolve the dye aggregates and bring the dye molecules to the water-fiber interface so that they can be easily absorbed by the fiber.
Dye carriers are used to assist in dyeing with disperse dye for synthetic fibers. Dye carriers allow even dyeing at boil with a reasonable dyeing time. Carriers are mainly used for the hydrophobic fibers that is to be dyed with disperse dye. The most important hydrophobic fiber Polyester can be dyed with disperse dye using carrier method.
Disperse dye can’t penetrate into the hydrophobic fiber like polyester as they have highly crystalline structure. Carriers should be selected carefully for maximum dye uptake and better dyeing performance.
Carrier action on fiber swelling helps to create free volume and molecular chain movement to allow the dyes in the fiber.
Considering factors for Dye carriers selection:
- Higher effectiveness
- Cheap in price
- No adverse effect on light fastness of dyed material
- Free from unpleasant odor
- No degradation of fiber
- Easily removable
- Easy dispersion in the dye bath
- Low volatility in steam
- Highly stable under dyeing condition
- Compatible with dyestuff and other chemicals
- Uniformity of absorption by the fiber
- Non-irritant on skin
- Don’t shrink the dyed materials
- No impact on handle of the dyed materials
Polyester dyeing at boil temperature is possible with carriers! We all know that polyester is highly crystalline fiber. So the dye molecules can’t penetrate inside the fiber. Carriers help to swell the fiber and open up the fibrous structure to allow the dye molecules and mechanically entrapped them inside the fiber.
There are different theories for carriers to increase the rate of dyeing:
- Increased swelling of fibers
- Increased water imbibition by “Vickerstaff”
- Transport theory by “Summer at el”
- Film formation by “Vickerstaff”
- Lubricity theory by “Vickerstaff”
- Loosening of fiber structure by “Peter at el”
Carrier action can be described as below:
- Carriers swell the fiber and ultimately cause relaxation.
- They may operate by opening up of the internal fiber structure and allow the dye molecules to diffuse more rapidly.
- They act as molecular lubricant and reduce inter-molecular forces operating in the fiber.
As a result, they reduces the glass transition temperature allowing the polymer chain movement and creating free volume thereby allowing the dye molecules to force in its way in.
- Carriers alter the dispersing properties of dye and physical properties of the fiber so that more dyes can transfer from the dye bath to the fiber than in the absence of these assistants.
- At normal pressure and temperature below 100℃, carriers increase the dyeing rate and permit dye migration within the fiber.
Level dyeing of disperse dye on polyester depends on the migration power of the dye which is affected by the nature and amount of the carrier, dyeing time, temperature and the shade.
The compound having ionizable and solubilizing group are less effective as carrier. So, there will be no agent which reacts with carrier and make it solubilized or ionized.
- Carriers increase the absorbency power of fibers and the absorbed carrier increases the dye uptake by creating liquid co- fiber.
With increasing weight, carrier efficiency increases but up to a certain limit beyond which the efficiency of the carrier decreases.
Trade names of Dye Carriers:
Emulsifiable biphenyl derivative
Pros of Dye Carriers
>Enables dyeing at atmospheric temperature and pressure.
>Lower dyeing time
>Dark shades are possible
Cons of Dye Carriers
>Can cause skin irritation
>May alter light fastness of the dyed materials
>Some carrier has strong odor
>Condensation of carrier vapor may leads to faults like oily spots
>Some are dye specific
>Can cause shrinkage of the dyed materials
>Greater volatility of some carrier can cause carrier spotting in open equipment.
>Some carriers tend to crystallise out below 80°C
>Risk of staining
Polyester can be dyed with carriers even at boil temperature. But polyester dyeing with dyeing carriers has some merits and demerits too.