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Enzymatic modifi cation of polyacrylonitrile and cellulose acetate fi bres 115

needs to be properly controlled in order to maximize the concentration of
the surface acidic groups.

5.4.2 Advantages and limitations of polyacrylonitrile
biomodifi cation
Table 5.4 summarizes the various reports of biomodifi cation of polyacrylo-
nitrile and its copolymers. Despite the different substrates, origin, and
amount of enzyme used (not forgetting the different methods used to
measure the initial activity applied in the treatments), it is obvious that, at
moderate temperature and pH conditions, it is possible to specifi cally
modify the nitriles of PAN into amides or carboxylic groups, with distinct
chemical properties. This is an important outcome implying that the use of

enzymes in the particular case of PAN, a non-natural fibre, is not an unob-
tainable concept but a feasible process. Several aspects, such as the staining
properties and hydrophilicity were clearly improved for the polyacryloni-
trile copolymers. A higher hydrophilicity is of great interest because it
would improve wear comfort (by increasing moisture uptake capacity and
reducing the static charge accumulation), dyeability, and fastness of some

finishes. Above and beyond the textile perspective, modified PAN is also of

interest to the filtration technology field where it is commonly applied in

reverse osmosis gas separation, ion exchange, ultrafiltration and dialysis
(Frushour and Knorr, 1998; Masson, 1995). The amide and/or carboxylic
groups at the surface of PAN would facilitate and open new routes for its
coating or functionalization in these particular technological areas (Huang
et al., 2005).
Huang et al. (2005) also inferred from their results that these transforma-
tions happened mainly at the surface of fi bres. Tauber et al. (2000) compared
several techniques (FTIR, Raman microspectroscopy and XPS) having dif-
ferent beam interaction depths inside the sample; only XPS (1–5 nm)
allowed differences to be detected in the chemical composition between
treated samples and controls. Wang et al. (2004) also analysed some samples

and controls by FTIR that showed no significant chemical changes in the
bulk fibre. In addition, they microscopically analysed cross-sections of

treated samples after acid staining and verified that the fibres were ring

dyed owing to the superficial action of nitrile hydratase. Matamá et al.
(unpublished results) confirmed the superficial action of a commercial

nitrilase conjugated with fl uorescein isothiocyanate (FITC). Cross-sections
of acrylic fibres were observed by fluorescence microscopy (Fig. 5.8) and

the fluorescence signal was located mainly at the surface, the core did not

emit fluorescence indicating that the conjugated enzyme did not penetrate

inside the fi bres.
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