Page 368 - Basic Principles of Textile Coloration

REFERENCES 357

the reformation of disulphide links, and reaction with non-keratinous proteins in
the cell membrane complex and endocuticle.

16.6.3 Semi-continuous methods for reactive dyes on wool
Reactive dyes can be applied to both wool cloth and tops by padding followed by
batching for 24–72 h. A thickener is added to the pad liquor to give a high
solution pick-up. High concentrations of urea are used and the solution also
contains sodium metabisulphite. Urea breaks up dye aggregates and sodium
metabisulphite reduces cystine crosslinks in the wool, generating more reactive
thiol groups. This promotes higher and more uniform fixation. The combination of
urea and metabisulphite (Na2S2O5, gives NaHSO3 on hydrolysis) in the padding
solution results in greater fibre swelling and better dye penetration. Dyes with
activated double bonds react with bisulphite by nucleophilic addition and are
converted into non-reactive forms so the pad solutions are not particularly stable.
The pad–batch method can be used with reactive dyes normally applied to cotton,
such as Procion MX and Drimarene K dyes. The dyed goods are then treated with
dilute ammonia, rinsed and neutralised with acetic acid to remove unfixed dye.
This type of process is very economical and reduces fibre damage.

REFERENCES

1. J Shore, in Cellulosics Dyeing, J Shore, Ed (Bradford: SDC, 1995).
2. D M Lewis, in Wool Dyeing, D M Lewis, Ed (Bradford: SDC, 1992).
3. A H M Renfrew, Adv. Colour Sci. Technol., 1 (1998) 12.
4. A H M Renfrew and J A Taylor, Rev. Prog. Coloration, 20 (1990) 1.
5. D A S Phillips, Adv. Colour Sci. Technol., 1 (1998) 1.
6. J A Taylor, Rev. Prog. Coloration, 30 (2000) 93.