Page 131 - Advances in Textile Biotechnology

112 Advances in textile biotechnology

an increase in K/S (Table 5.3). The XPS analysis clearly demonstrated the
conversion of nitrile groups into amides without further hydrolysis, despite
the presence of amidases in the cell-free extracts, as also verifi ed by Tauber
et al. (2000).
Another microorganism, Agrobacterium tumefaciens, was found to grow
on PAN as a carbon source, converting it to polyacrylic acid (PAA) as
shown by solid state nuclear magnetic resonance (NMR) (Fischer-Colbrie
et al., 2006). The crude enzyme preparation isolated from the bacteria cells
showed activities of both nitrile hydratase and amidase. PAN powder and
fabrics were treated over 24 and 48 h, respectively, with crude enzyme
preparations in a special stabilizing buffer, at 30 °C. The nitrile groups were
converted either to amides or to carboxylic groups, depending on the reac-
tion conditions (time of incubation and enzyme activity) and on the type

of substrate. Once more, the amidase was less efficient in using acrylic fabric
as a substrate, as found in other studies for amidases from other species.
The ammonia was only detected after prolonged enzymatic treatment of
PAN fabrics. Fischer-Colbrie et al. (2006) proposed the higher surface area
of PAN powder compared with PAN fabrics as a cause of the higher yield
of conversion to carboxylic groups in the powder. This work confi rms that
the nitrile hydratase is more active on PAN than amidase, resulting primar-
ily in the formation of amides when such enzyme system is used.
More recently, two reports were published referring to the complete

biomodification of nitrile groups of PAN into carboxylic groups (Fischer-
Colbrie et al., 2007; Matamá et al., 2007).
A membrane-bound nitrile hydrolysing enzyme was isolated from Micro-
coccus luteus BST20 by Fischer-Colbrie et al. (2007). Nitrile groups from
both PAN powder and fabrics were converted to carboxylic acid groups,
with the associated release of ammonia (5% of the theoretical possible
amount for PAN powder). The fabrics treated with nitrilase showed higher
K/S values when dyed with methylene blue than the fabrics treated with
inactivated enzyme or without any enzyme at all. The results demonstrated
that this micro-organism is an interesting source of enzymes for modifying
the surface of PAN, producing acid groups as opposed to the previous
nitrile-degrading enzymatic systems.
Acrylic fabrics composed of a copolymer of PAN and 7% w/w vinyl
acetate were treated with a commercial nitrilase (Matamá et al., 2007). The
effect on nitrilase stability of the two most common PAN solvents, DMF
and dimethylacetamide (DMA), and of polyalcohols was studied in order
to establish a media composition that would favour the accessibility of PAN
fabrics/fibres to nitrilase, without compromising the enzyme stability more

than necessary. Treatments performed at 30 °C over 5 days, in the presence
of 4% v/v DMA and 1M sorbitol, led to an improvement in the colour
strength of treated fabrics (17% increase in K/S values compared with the

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