Page 286 - Advances in Textile Biotechnology

Enzymatic functionalization of cellulosic fi bres for textiles 267

following liberation from the plant tissue source. This may involve selec-
tive removal of components, such as associated lignin, hemicelluloses and
extractives, by pulping and bleaching chemicals to improve the optical

properties of the final paper or textile product. Realization of the full

potential of cellulosic fibres, however, requires the addition of chemistry
to the fibre surface in many applications. Some common examples

include the application of strength-building compounds, retention aids,

hydrophobic molecules, and inorganic fillers during papermaking, as
well as the binding of dyes, optical brighteners, and sizing agents to textile

fibres and fabrics. Clearly, the need for surface functionalization extends

to high performance products based on cellulose fibres, such as ‘smart’
textiles, electronic paper, cellulosic biocomposite materials, and biomedical
devices.
Indeed, a wide range of classical chemical methods have been developed
to modify cellulosic fibre surfaces, either through physical adsorption or

direct covalent attachment of molecules. Although powerful, the covalent
derivatization of cellulose has certain limitations. Cellulose polysaccharide
chains exist as insoluble, paracrystalline aggregates, which are characterized
by low reactivity of the tightly hydrogen-bonded hydroxyl groups. Further,
extensive reaction of these same hydroxyl groups leads to disruption of
cellulose crystallinity, chain degradation, and, ultimately, a loss of fi bre
strength (Sassi and Chanzy, 1995; Sassi et al., 2000; Klemm et al., 2005). In
some cases, reactions may require non-aqueous media, thus necessitating a
solvent exchange or drying step, which may result in altered cellulose mor-
phology or be technically impractical on a large scale. These concerns are
particularly relevant for cellulosic hydrogels, such as bacterial cellulose or
microfibrillated cellulose/nanocellulose suspensions, which are emerging as

promising new biomaterial templates (Bodin et al., 2006, 2007a, 2007b;
Henriksson et al., 2008; Iwamoto et al., 2005; Nakagaito and Yano, 2005;
Yano et al., 2005).
With the potential of cellulosic fibre functionalization in focus, a number

of years ago our laboratory began work on a biomimetic approach to cir-
cumvent the inherent challenges of direct chemical approaches. In this
approach, the strong interaction of cellulose with the cell-wall-matrix poly-
saccharide xyloglucan (XG) was harnessed, together with the unique cata-
lytic properties of an endogenous plant transglycosylating enzyme,
xyloglucan endo-transglycosylase (XET). The subsequent sections will
provide an overview of some of the basic biochemistry of XG and XET in
the context of the plant cell wall, and highlight how this system has been
appropriated, in conjunction with organic chemistry, to install a range of

functional groups on cellulose fibres. The practical application of this system
has a strong foundation in the historical use of native XG as a sizing agent
in textile and paper industries.

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