Page 137 - Basic Principles of Textile Coloration

126 PROTEIN FIBRES

NH CO(CH2)4 CONH (CH2)2 NH (CH2)2 NH CO (CH2)4 Polyamide

n

+ CH2 CH CH2Cl

O

(CH2)2 N (CH2)2 (CH2)2 N (CH2)2
CH2 CH2
CH OH CH O
CH2
CH2Cl

(CH2)2 N (CH2)2 H
(CH2)2 N (CH2)2
H2C CH2
CH2
CH CH OH
CH2OH Hydrolysis product
OH Hercosett polymer

N CH2 CH CH2 S CH2 Wool N CH2 CH CH2 NH Wool
OH OH

Polymer fixed to a wool thiol group Polymer fixed to a wool amino group

Figure 7.6 Chemistry of the Hercosett process for shrink-proof wool

effect, and by welding fibres together at their contact points. The polymer can be a
polyamide produced by interfacial polymerisation, or a silicone or polyurethane
coated onto the fibres using an organic solvent. A curing step is usually needed to
fix the film of polymer onto the surface scales.

Several different testing procedures are used to evaluate the shrinkage of wool
fabrics or articles. These involve evaluation of the relaxation and felting shrinkage
in standardised washing and felting procedures. As with other chemical
treatments of wool, shrink-resist processes cause some damage to the fibres. This
can be assessed by dyeing and wool solubility tests. Damaged wool invariably gives
a higher rate of dye absorption and is more readily soluble in dilute NaOH
solution, or in solutions of urea and sodium bisulphite. The evaluation of fibre
damage is important because damaged wool is less resistant to repeated washing
and to abrasion [5].