Page 144 - Advances in Textile Biotechnology

Enzymatic modifi cation of polyacrylonitrile and cellulose acetate fi bres 125

2001). Therefore, the impact of enzymes is dependent on our ability to tailor
their properties according to the demands of a particular technological
process. Some important issues that often need to be addressed are: limited
substrate range; limited stability to temperature, pH and solvents; limited
enantioselectivity; and limited turnover number (Powell et al., 2001).
Although screening naturally occurring enzymes continues to be an impor-

tant approach to find better biocatalysts, the manipulation of the protein
molecule itself and/or the reaction media are gaining increasing importance
and becoming essential for the competitiveness of bioprocesses. Neverthe-
less, both maximizing those enzymes found through natural diversity and

the optimization strategies are necessary to achieve the final goal of having
a novel enzyme addressing the exact and specific demands of an industrial

enzyme application.
Although here we are concerned with textile biotechnology, PAN and
cellulose acetate are materials of increasing interest for other areas where
surface modification is important in their application. Owing to its excellent

mechanical properties, stability and low cost, PAN is used in water treat-

ment, protein immobilization, ultrafiltration and dialysis (Wang et al., 2007).

Cellulose acetate also finds many non-textile applications such as desalting
(by reverse osmosis), hemodialysis, drinking-water purifi cation (by ultrafi l-

tration), as filters for laboratory use, and as stationary phases in chroma-
tography (Shibata, 2004).
In membrane processes, protein fouling and biocompatibility (biomedical

field) are major problems. The main driving forces for these undesirable
adsorption processes are electrostatic, hydrophobic and entropic effects
(Wang et al., 2007). To improve the performance of the membranes, the
general approach is to make the surface hydrophilic. In some applications,
biocompatibility is also an important and complex issue that can be
addressed by the immobilization of certain molecules, to provide reactive
functional groups at the surface (Wang et al., 2007).
Materials made from PAN or cellulose acetate with no or few chemically
reactive functional groups need a surface activation process to create sites
for further grafting or immobilization. So far, the surface activation has
been accomplished through chemical or physical processes (Deng and Bai,
2003, 2004; Huang et al., 2005; Jia and Yang, 2006; Lin et al., 2004; Wang
et al., 2007; Yim and Sefton, 2009). Enzymes are the future of surface activa-
tion, and membrane technology will probably be a future application of
biomodified PAN and cellulose acetate. For these two materials, enzyme

engineering is still an unexplored research area or in the early stages of
development, and it is urgent to address it for the simplification of modifi -

cation processes and to give a wider range of PAN and cellulose acetate
applications.

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