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.
Tuesday, 2 January 2024
Solvent dyeing
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