Page 342 - Advances in Textile Biotechnology

Hydrolysis of regenerated cellulose fi bres for textiles 323

14
60 min
12 180–240 min
Hydrolysis rate (g l –1 h –1 ) 8
10

6

4
2

0
0 1 2 3 4 5 Liq. NH 3
–1
[NaOH] (mol l )
13.5 Cellulose effect of alkali pretreatment on hydrolysis rate of
viscose fabric as function of alkali concentration, hydrolysis activity
given as concentration of glucose formed per hour and per litre (Liq.
NH 3 indicates pretreatment in liquid ammonia) (Schimper et al., 2009).

60 min of cellulase treatment and during the 4th hour of hydrolysis, of
samples, which were treated in the ‘never dried state’ without intermediate
drying.
During the first 60 min of treatment, the distinct increase in hydrolysis

rate can be explained by the activation of the viscose fibre, obtained during

the preceding alkalisation. Thus, the maximum activation is observed above
−1
a NaOH concentration of 2.3 mol l , near the swelling maximum reported
for viscose fibres. For interpretation of the activation effects in 3.5 and

−1
4.9 mol l NaOH, it has to be considered that a fi bre treated in these solu-
tions passes the swelling maximum twice, during impregnation and during
the washing procedure.
Samples that were dried before enzymatic hydrolysis showed a consider-
ably lower hydrolysis rate. Both line-dried and freeze-dried samples were
hydrolysed much more slowly than samples hydrolysed directly in the wet
state without drying (Table 13.3).
The distinct effect of activation is explained by the creation of more easily
accessible cellulose regions owing to enlarged pores and a greater inner
surface area. Intensive structural reorganisation of the fibres makes the

surface of the fibres more susceptible to cellulase sorption and hydrolysis

reactions. During drying, weakly adsorbed water is removed and a part of
the pores formed or expanded during the alkalisation step collapses. As a
result, overall cellulose activity decreases.

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