Page 335 - Advances in Textile Biotechnology

316 Advances in textile biotechnology

reesei cellulase is assumed to be 35–75 Å for a spherical shape, and is esti-
mated between 20 × 110 and 40 × 250 Å for an ellipsoid form (Buschle-
Diller et al., 1994). Comparing the size of enzyme proteins with the pore

size distribution of cellulose fibres, Bredereck and Gruber (1995) concluded
that the hydrolysis is expected to proceed mainly at the surface of the
swollen fi bres. Degradation inside the fi bre structure can only proceed in a
few pores, which have a diameter large enough to permit access to the cel-
lulase proteins. Thus, enzymatic hydrolysis of viscose, modal and lyocell
starts from the surface of the fi bres.
Analysis of pore size distribution by ISEC indicates a reduction of pore
volume after enzymatic hydrolysis for lyocell fibres, whereas an increase

was measured for viscose fibres and to a lower extent for modal fi bres. These
differences were explained by Bredereck and Gruber (1995) in terms of the
different pore size distribution in the cross-section of lyocell type fi bres and
viscose/modal fi bres.

The hydrolysis of viscose fibres was also studied by scanning electron
microscopy (SEM) and atomic force microscopy (AFM). Differences
between a total crude cellulolytic complex and endoglucanase-enriched

neutral cellulolytic enzymes were observed for viscose fibres. A total crude
enzyme removes fuzz, pills and impurities from the fabrics surface and
leaves distinct cavities and indentations along the length of macro-fi brils.
When viscose fi bres are treated with endoglucanase-enriched enzymes, the
major process is peeling and smoothing of fibre surface (Kokol, 2003).

Similar differences between the action of exoglucanases (cellobiohydrolase,
CBH) and endoglucanases (EG) were reported for cotton fi bres, where
CBHs were shown to produce indentations in the fibre structure, whereas

EGs smoothen and peel the surface of the fi bres (Lee et al., 2000).
In a systematic study of the adsorption of a total crude cellulose, Shen
et al. (2002, 2004) compared the adsorption on cotton, viscose and fl ax fi bres.
As a result it could be demonstrated, that viscose fibres offered the greatest

number of sites for adsorption of enzymes, the largest surface area available
for enzyme coverage, and the maximum volume that can be occupied by
cellulases. The relative magnitude of these parameters being 4 : 2 : 1 for
viscose, cotton and fl ax, respectively.

Compared with cotton fibres, man-made cellulose fibres show a greater
variability in sorption and swelling behaviour depending on the processing
steps in textile production, thus observed cellulose reactivity is infl uenced
by the conditions applied during the preceding treatment steps.

13.4 Cellulase hydrolysis of regenerated
cellulose fi bres
In a total crude cellulose, three main types of enzymes are active. Endoglu-
canases or endocellulases hydrolyse cellulose polymers randomly along the

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