Page 290 - Advances in Textile Biotechnology

Enzymatic functionalization of cellulosic fi bres for textiles 271

Using a flow loop system, Yan et al. (2006) demonstrated that the effect

of improved formation was the result of reduced fi bre flocculation in the
wet-end of the papermaking process. Rutland and co-workers, working in
collaboration with our group, have used cellulose colloidal probe atomic
force microscopy (AFM) to perform fundamental surface force measure-
ments of the cellulose–XG interaction in the context of papermaking (Nor-
dgren et al., 2008; Stiernstedt et al., 2006a, 2006b). These results suggest that
XG forms a boundary lubricating layer, which reduces friction and allows

fibres to more easily slip past one another in the wet state, thus rational-
izing the observed improvements in sheet formation. Paradoxically, cellu-
lose adhesion is also enhanced by XG (decreased friction is almost always
associated with decreased adhesion behaviour). Wet cellulose surfaces in
contact display almost no adhesion, but when coated with an adsorbed XG

layer, a significant time-dependent adhesion is manifested. This implies that
the XG, although essentially irreversibly adsorbed, is nonetheless able to
reorient and bind to an opposing surface on time scales of the order of a
few seconds to minutes. This probably contributes to the increased paper

strength observed with XG-treated pulps, because fibre bonds achieve sig-

nificant adhesion levels before drying owing to bridging effects (Stiernstedt
et al., 2006a). Interestingly, the crosslinking of macroscopic cellulosic fi bres
by XG in paper and textiles may be analogous to the crosslinking of cel-
lulose microfi brils by XG within the cell wall (Carpita and McCann, 2000).

The capacity of wood pulp fibres to bind XG is closely correlated with the
chemical composition of the fibre surface. Mechanical pulps, which have a

high amount of residual surface lignin and extractives, bind less XG than
chemical pulps with low lignin and hemicellulose content (Zhou et al.,
2006a).

11.3.2 Composites from xyloglucan and cellulose fi brils

In addition to whole plant fibres, complexes of pure cellulose micro/nano-

fibrils with XG have received continued attention owing to their relevance
in understanding the molecular basis of plant cell wall morphology, see
Whitney et al. (2006) and references therein. For bacterial cellulose com-
posites, further processing with XG-active enzymes has been used to alter
mechanical properties (Chanliaud et al., 2004). Several studies have under-
scored the remarkable physical properties of cellulose networks based on
bacterial (Yano et al., 2005) and plant nanofi bres (Iwamoto et al., 2005),
including microfibrillated cellulose from wood pulp (Henriksson et al., 2008;

Nakagaito and Yano, 2005). The admixture of cellulose nanofibres with XG

thus represents an interesting new area of biofibre composite design that
has, as yet, been little explored.

© Woodhead Publishing Limited, 2010