Solvent dyeing

 Solvent dyeing is a dyeing process which is carried out from a continuous non aqueous phase. Here solvent is used as dyeing media but water may be added to assist the dyeing process. Where ionic reactions are not involved as in dyeing hydrophobic fibres with disperse dyes, it has been established that within limits dyeing in solvent is a practical proposition. The dyes are soluble in the solvents and the solvent carries the dye molecules to the interior of the fibre and then recovered. Solvent dyeing is not effective for natural fibre dyeing. It is only suitable for dyeing man made fibres mainly polyester, nylon and acetate.

In Bangladesh solvent dyeing process has not been introduced. But, in India there are some solvent dyeing plants. Now a day’s solvent dyeing is used only to dye polyester fibres. In 1928, alcohol and water mixtures were suggested to dye the secondary acetate. Many solvents (e.g. ethylene glycol) have been examined, but attention had tended to concentrate on chlorinated solvents due to their extensive use in dry cleaning and scouring. The chlorinated solvents differ from water and they are able to wet almost all fibres rapidly and efficiently and can readily be
removed from the fibre by hot air or steam. Specially 3 chlorinated solvents are extensively used in
solvent dyeing namely

1) Trichloroethylene- Popular in U.K ,because it is produced by British company I.C.I
2) Perchloroethylene- More interesting than TRI due to its higher boiling point. Most widely used
as it is popular in dry cleaning used in European countries except U.K
3) 1, 1, 1- Trichloro ethylene (Methyl chloro form) – Used in U.S.A

Besides the above three solvents, Methyl chloride, Carbon tetra chloride and Ethylene alcohol are
also used in lesser extent in solvent dyeing.

Necessity of solvent dyeing:
Solvent dyeing is on focus due to
1) Fresh water unavailability.
2) Waste water disposal problem.
3) Considerable energy saving because solvents usually have much lower heat of evaporation than water.
4) Solvents can be more or less completely recycled by means of standard recovery operations.
5) It can eliminate costly dyeing process and potential water pollution problem.