Page 334 - Advances in Textile Biotechnology

Hydrolysis of regenerated cellulose fi bres for textiles 315

Table 13.1 Representative fibre data of man-made cellulosic fibres and cotton:
degree of polymerisation, porosity and BET moisture regain
Parameter Unit Viscose Modal Lyocell Cotton
c
c
b
Water retention ml g −1 0.88 , 0.89 d 0.62 , 0.64 d 0.71 , 0.71 c 0.56 d
value WRV
a
ml g −1 0.64 a 0.49 a 0.53 , 0.58 b 0.31 a
Pore volume V p
a
Average pore Å 29 a 24 a 29 , 32 b 35 a
diameter
a
2
Pore surface m g −1 438 a 408 a 365 , 369 b 177 a
Moisture content % 9.98 d 9.64 d 9.23 e 5.54 d
(20 °C, 60% RH)
c
BET moisture mmol g −1 3.05 c 2.99 c 2.73 , 2.79 e 1.59 e
regain V m
a
Determined by inverse size exclusion chromatography (ISEC) (Bredereck and
Gruber, 1995).
b
Öztürk et al. (2009).
c
Siroka et al. (2008).
d
Okubayashi et al. (2005).
e
Okubayashi et al. (2004).
inverse size exclusion chromatography (ISEC) and data describing mois-
ture sorption are given. The Brunauer-Emmet-Teller (BET) value V m char-
acterises the moisture regain corresponding to a monomolecular layer on
the substrate. A more extensive comparison of fibre properties of lyocell,

viscose and modal has been presented by Kreze and Malej (2003).
The values in Table 13.1 show distinct differences between the man-made
cellulosic fibres and cotton fibres, which exhibit approximately half the

sorption capacity and internal surface area. The much lower pore volume
V p and also the lower water retention value (WRV) indicate lower expan-
sion and swelling of the cellulose structure for cotton.
13.3 Cellulases
For cellulose hydrolysis, the cellulases have to access the surface of the cel-
lulose fibre, then the enzyme binds with the cellulose binding domain to the

polymer structure. Thus, porosity of the cellulose fibre and reactivity of

surface will influence the degradation rate of the enzymes. For the swollen
cellulose fibre, the cellulose surface is best illustrated by a water-containing

boundary layer formed between highly ordered parts of the cellulose fi bre
and fully hydrated, less ordered parts of the three-dimensional polymer
structure. This layer can be assumed to show a gradual change in ‘cellulose
concentration’, from high polymer density inside the fibre to pure solvent

outside the fibre. The molecular size of enzyme proteins e.g. Trichoderma

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