Page 199 - Advances in Textile Biotechnology

180 Advances in textile biotechnology

proteases. Oxidative treatments of wool can disrupt disulfide bonds and

open up the wool fibre surface assisting enzymatic attack on the cuticle. In
addition, oxidative pre-treatment probably causes a partial removal of the
fatty acid barrier from the epicuticle, which confers hydrophilicity to wool
(Cardamone et al., 2005). Consequently, the enzymatic attack on the cuticle
can be selectively activated. It has been claimed that a combination of
chlorination with chlorine gas or dichloroisocyanuric acid and subsequent
enzyme treatments with a protease such as papain showed that pre-
oxidation will limit enzymatic attack to the cuticular layer, resulting in the

enzymatic descaling of wool fibres to enhance not only lustre but also
shrink-resistance (Levene and Shakkour, 1995; Moncrieff, 1953). However,
the process may cause fabric yellowing.
Recently a two-step process which combines bleaching, shrinkage pre-
vention and biopolishing was suggested as a way to make wool feel silky
smooth. This involved a pretreatment using hydrogen peroxide enhanced
by dicyandiamide and stabilised by gluconic acid allowing powerful oxida-
tion. This was followed by treatment with proteases in the presence of

sodium sulfite in triethanolamine buffer solution. Benefits claimed were a

high level of whiteness, the removal of protruding fibre ends for fabric

smoothness and shrink-resistance (Cardamone et al., 2004 and 2005).
Other oxidising agents used as a pre-treatment for wool are peroxymono-
sulfuric acid, peracetic acid and potassium permanganate. Alkali and reduc-

ing agents such as bisulfite can alternatively be used to open disulfi de bonds
in the cuticle scales to make the fibre more susceptible to enzyme attack.

These pre-treatments have been reported to enhance the activities of pro-
teases and improve the efficiency of proteases in conferring anti-felting and

shrink-resistance of wool (El-Sayed et al., 2001; Levene and Shakkour, 1995;
Levene et al., 1996). However, these processes caused severe fi bre damage
when shrink resistance was reaching adequate levels for machine-washable
wool. Recently, Lenting et al. (2005 and 2007) used the addition of a high
concentration of sodium salt in a peroxide pre-treatment to restrict the

oxidative reaction to the surface scale of wool fibres. This resulted in an
improvement in the susceptibility of the protein layer in the outer surface
to subsequent proteolytic hydrolysis. This agreed with an earlier study
which suggested that the presence of high concentrations of salt lowered
the swelling of the fibre and lowered the rate of diffusion of the oxidant

through the cuticle to the cortex. This led to preferential attack on the
cuticle (Maclaren and Milligan, 1981) and wool shrink resistance was
claimed without substantial loss of fibre tensile properties.

Although there is currently considerable interest in the use of enzymes
to achieve shrink-resist finishing on wool, it is apparent that the results of

enzyme treatments, especially with proteases, can be unpredictable and may
sometimes lead to unacceptable degradation of the fi bre.

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