Page 128 - Advances in Textile Biotechnology

Enzymatic modifi cation of polyacrylonitrile and cellulose acetate fi bres 109

For both fibres, the enzyme introduces chemical groups that are more

hydrophilic than the original ones; therefore it is also possible to indirectly
assess the biomodification using methods that determine the hydrophilicity

of materials. It may also be relevant to evaluate any changes that may occur
in physical properties of the fibres such as mechanical performance (strength,

elongation/elastic recovery, and resiliency) and electrical conductivity, using
standard testing procedures. Valuable information can also be inferred from
high-resolution surface images of treated materials. Scanning electron
microscopy (SEM) is one of the most widely used analytical tools owing to
the extremely detailed images it can provide. In addition, when it is coupled
to an auxiliary energy dispersive x-ray spectroscopy (EDS) detector, this

technique also offers elemental identification. Scanning transmission elec-
tron microscopy (STEM) has better spatial resolution and is capable of
additional analytical measurements, such as crystallographic phase or ori-
entation characterization (Niemantsverdriet, 2007).
Whatever the method of choice, there is a factor that has to be carefully
controlled: the amount of adsorbed protein that will interfere with the
measurements. Efficient washing after enzymatic treatments is essential

and, once again, good controls that use enzymes without activity (null
mutants) but with the same adsorption profile are very important.

5.4 Polyacrylonitrile biomodifi cation

5.4.1 Nitrile-metabolizing enzymes for the modifi cation of
polyacrylonitrile

Tauber et al. (2000) reported the modification of PAN using crude enzyme
preparations from the strain Rhodococcus rhodochrous NCIMB 11216: a
nitrile conversion to the carboxylic acid with the release of ammonia, on
granular PAN as substrate, and a nitrile conversion to the amide on acrylic

fibres. In cell preparations, both nitrile hydratase and amidase were detected
−1
(at 30 °C and pH 6.5, the nitrile hydratase activity was 14.2 nkat mg of cell
dry weight using acrylonitrile as substrate and the amidase activity was
−1
1.7 nkat mg of cell dry weight using acrylamide as substrate). Two granu-
lar PAN standards were used, having different molecular weights (40 and
190 kDa). The enzymatic treatments of granular PAN were performed in
57 mM phosphate buffer pH 7, at 25 °C for a maximum period of 72 h,
under vigorously shaking (300 rpm). The enzymatic system of nitrile hydra-
tase/amidase was able to partially complete the hydrolysis of the nitrile to
carboxylic groups, in both granular PAN standards, as indicated by the
release of ammonia, although, the molecular weight of PAN negatively
infl uenced the action of enzymes. When acrylic fabric samples (PAN copo-
lymer containing 7% w/w of vinyl acetate) were treated at 30 °C for the

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