Page 137 - Advances in Textile Biotechnology

118 Advances in textile biotechnology

(a) (b)

0 μm 25 0 μm 25

5.8 Epifluorescent photographs of cross-sections from (a) acrylic

controls and (b) treated samples. The samples were treated with
FITC-conjugated nitrilase at pH 8 and 30 °C, for 15 h. Both images
were acquired with a total magnifi cation of ×1000.

Although the superficial action of nitrile degrading enzymes was demon-
strated in the examples studied, the fact that the desirable bulk properties,
such as the mechanical properties, of PAN fibres remained unaffected was

not verified in practice. The study of mechanical properties is a pertinent

subject, to ascertain the impact of the enzymatic modification on PAN

materials, especially, when the nitrilase was used and the PAA was detected
in solution as a secondary product.

The modification of a solid substrate with enzymes constitutes heteroge-
neous biocatalysis because enzyme and substrate are in different phases.
Therefore, it is necessary to consider two general steps in order to make
the catalysed reaction occur: the physical adsorption of the enzyme (includ-
ing the transport of enzyme molecules from the bulk solution to the sub-
strate surface) and the formation of an active enzyme/substrate complex
that will lead to the desired product and to the regenerated enzyme. This
type of enzymatic catalysis is, in general, less efficient than in homogeneous

systems because of steric constraints, mass transfer and partition effects. The
use of certain additives served the main purpose of increasing the accessibil-
ity of PAN to enzymes. The organic solvents DMF and DMA were chosen
because of their action on the fibre structure. They are known solvents of

PAN and they are commonly used in the industrial production of acrylic
fibre (Burkinshaw, 1995; Capone, 1995). Their plasticizer function disturbs

the regular structure of the polymer, reducing the magnitude of interchain
bonding, which should aid accessibility to the enzyme, improving its action

on the fibre. The results showed that DMF had an effect dependent on its
concentration that was best around 0.5% (v/v) for nitrile hydratase, not
taking account of the different enzyme sources (Tauber et al., 2000;
Battistel et al., 2001; Wang et al., 2004). The tested concentration of the non-

ionic surfactant JFC was beneficial as was a mixture of DMA and sorbitol

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