Page 198 - Advances in Textile Biotechnology

Enzymatic treatment of wool and silk fi bres 179

of the covalently bound lipids from the wool surface even after prolonged
treatment time. It was believed to be associated with the accessibility of
cutinase active sites toward the outmost hydrophobic bound lipids in the

wool fibre surface. Treatment of wool fabrics with cutinase has the potential

to improve the wettability and facilitate the shrink-resist finishing of wool
fabric by the subsequent treatment with proteases.
Other chemical methods of lipid removal have been studied to make the

wool fibre more hydrophilic, which may make the subsequent enzyme

shrinkproofing treatment more efficient. These chemical methods are: treat-

ment with a cationic surfactant, preferably an alkylammonium halide such
as cetyltrimethylammonium bromide (CTAB) or cetyltrimethylammonium
chloride (CTAC), in alkaline conditions (Julie et al., 1985; Smith et al., 2010);
treatment with hydroxylamine and a non-ionic surfactant at pH 7–8 (Meade
et al., 2005, 2008); treatment with potassium tert–butoxide under anhydrous
conditions (Leeder and Rippon, 1985; Meade et al., 2008).
Pretreatment with cetyltrimethylammonium bromide (CTAB) in alka-
line conditions can make the fi bre become very hydrophilic because of the
removal of surface lipid. It was found, however, that residual CTAB on the
fi bre significantly decreased activity of proteases. After CTAB treatment,

thorough washing with anionic surfactant in acidic conditions was required
to maintain the enzyme activity. It was found that the activity of a protease

enlarged by chemical modification was improved on wool that had been
treated with CTAB and washed with anionic surfactant, because chemical
modification made the enzyme more resistant and stable (Smith et al., 2010).

A two-step treatment consisting of a low-temperature plasma treatment
(LPT) and subsequent enzymatic treatment by proteases has also been
investigated to modify the cuticle cells to achieve wool shrink resistance
(Dybdal et al., 2001; Jovancic et al., 2003). X-ray photoelectron spectroscopy
(XPS) analysis revealed that the LPT/enzymatic treatment completely
removed the outermost lipid layer (the F-layer) of the epicuticle. However,

in order to avoid excessive damage to wool fibres, the subsequent enzymatic
treatment was mostly used to remove fibre ends protruding from the surface

of the fabric and thus increase its softness.
In order to achieve machine-washable wool, severe treatments with pro-
teases are required to degrade the cuticlar cells of wool fibres. It is diffi cult

to avoid signifi cant fibre damage caused by proteases. Scientists have made
great efforts using different wool pre-treatments before enzyme treatment
in order to limit enzymatic degradation to the cuticle scales. Various com-
binations of enzymes, oxidants/reductants and polymers have been pro-
posed to improve resistance to felting and shrinking of wool (Cardamone
et al., 2006; Jovancic et al., 1998; Levene and Shakkour, 1995; Levene et al.,
1996). In some of the early enzyme-finishing processes, wool was pre-treated

by chlorine or hydrogen peroxide before incubating the fi bres with

© Woodhead Publishing Limited, 2010