Page 138 - Advances in Textile Biotechnology

Enzymatic modifi cation of polyacrylonitrile and cellulose acetate fi bres 119

in the treatment with nitrilase (Matamá et al., 2007; Wang et al., 2004). The
available data shows the possibility of improving the action of these nitrile-
degrading enzymes on PAN by manipulating the treatment media or, from
another perspective, the possibility of their application in the PAN wet
spinning process, which uses the already mentioned organic solvents
(Capone, 1995).
One important issue involving the application of enzymes to textile mate-
rials is the mass transfer of enzymes in textile wet processes as discussed
by Nierstrasz and Warmoeskerken (2003). Mass transport across a porous
material of large molecules like enzymes is a relatively slow process and
dependent on the properties such as the porosity and density of fabrics.
Unfortunately, it is not always clear in published works if PAN fi bres refer
to loose fi bres or to fabrics, and when fabrics are clearly used their charac-
teristics are not always provided. Different textile structures will have dif-

ferent outcomes in time and homogeneity of the biomodifications and it is
important to know which ones are used to have a more realistic perspective.
The enhancement of mass transfer during the enzymatic treatment is nor-
mally accomplished by mechanical agitation; in a lab scale, the horizontal
agitation is the most frequent though vertical agitation (simulating the
laundry washing machines) was also used in the treatment of PAN (Tauber
et al., 2000; Matamá et al., 2007). The applied mechanical forces that imply
a deformation of the porous matrix of the textile material (as it happens in

general on industrial equipments) will lead to a higher flow rate in the
intra-yarns pores and consequently to a faster and more homogeneous
biocatalysis (Nierstrasz and Warmoeskerken, 2003).
Other important aspects of biocatalysts are their stability under opera-
tional conditions and their ability to be reused in an industrial process.
Nitrile-degrading enzymes, in particular purified nitrilases, have an intrinsi-

cally low stability (Harper, 1977 and 1985; Bandyopadhyay et al., 1986). The
reported enzymes (Table 5.4) were used as cell lysate preparations, either
centrifuged or not, in order to guarantee the highest activity and stability;
it was observed that the nitrile hydratase activity was associated with cell
membranes fraction (Battistel et al., 2001; Fischer-Colbrie et al., 2007).
Matamá et al. (2007) observed that the adsorption of nitrilase on acrylic
fabric led to stabilization of the enzyme (a linear increase in ammonia over
36 h of treatment at 40 °C, Fig. 4.6), similarly to the immobilization pro-
cedures employed to stabilize proteins. Even in the case of enzyme stabili-
zation upon adsorption to PAN substrates, it would be interesting to look
for naturally more stable nitrile-degrading enzymes, such as those found in
extremophile micro-organisms (Cowan et al., 1998; Khandelwal et al., 2007;
Liu et al., 2008 Mueller et al., 2006; Pereira et al., 1998), because the presence
of high temperatures and organic solvents during the wet processing of
acrylic fibres can have deleterious effects on their activities.

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