Page 139 - Advances in Textile Biotechnology

120 Advances in textile biotechnology

The ability of enzyme recovery and recycling as well as a general improve-
ment in the long term operational stability is commonly achieved by bio-
catalyst immobilization (Bornscheuer, 2005). When dealing with PAN
substrates, the immobilization of the enzyme is not in theory a good option
because it creates a barrier to mass transfer and diffusion phenomena. The
industrial enzyme recovery or elimination requires other methods such as
size exclusion chromatography and pH/temperature shifts (Lenting, 2003).
The production of known nitrile-degrading enzymes that can be rede-

signed to use more efficiently PAN as a substrate is, beyond doubt, needed.
The incubation times necessary to produce the desired surface modifi ca-
tions are too long for a large-scale industrial application. In order to achieve

a proper control over the acrylic biomodification it is also important to have
a better understanding of how nitrilase acts on such a substrate. Is the

enzyme very sensitive to the crystallinity degree of the fibre? How does
crystallinity affect the release of polyacrylic acid? How is the molecular size
of the polymer related to the released amount of polyacrylic acid? Is there

any difference in treating the fibre before and after orientation? Before any
attempt to design a full-scale industrial process, the enzymes themselves
need to be engineered and further optimized at a laboratory scale.

5.5 Cellulose acetate biomodifi cation

5.5.1 Esterase for the modifi cation of cellulose acetates
Matamá et al. (2010) reported the superficial hydrolysis of acetate surface

groups of cellulose diacetate (CDA) and cellulose triacetate (CTA) fabrics
using cutinase (EC 3.1.1.74) from Fusarium solani pisi. Cutinase is a serine
esterase from the superfamily of α/β-hydrolases (Longhi and Cambillau,
1999) and it also belongs to the family 5 of carbohydrate esterases, sharing
a similar 3D-structure with two other members with known structure: the
acetylxylan esterase (E.C. 3.1.1.72) from Trichoderma reesei and the acetyl-
xylan esterase II from Penicillium purpurogenum (Ghosh et al., 2001;
Hakulinen et al., 2000). However, the active centre F. solani pisi cutinase
reflects a preference for hydrophobic substrates, a suitable and versatile

feature to be chosen for surface modification of highly substituted cellulose
acetates, together with the fl exibility of cutinase in using soluble and insol-
uble substrates (Ghosh et al., 2001).
To evaluate the effect of enzyme concentration, the release of acetic acid
was determined for samples of CDA and CTA fabric incubated over 8 h
with various esterase activity concentrations, at 30 °C and pH 8. The acetic
acid production increased over the range of the tested enzyme concentra-
tions. At the maximum enzyme concentration used, the acetyl esterase
activity was 0.010 and 0.007 U which corresponded to a release of 0.54 and

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