Page 341 - Advances in Textile Biotechnology

322 Advances in textile biotechnology

FWA uptake were observed, with more distinct effects being observed for
NaOH-treated samples (Öztürk et al., 2009). In particular, regenerated cel-

lulose fibres show remarkable potential for reorganisation of the fi bre struc-
ture which also alters the cellulose hydrolysis rate.
The effect of treating lyocell fabric with 8% NaOH solution on the cel-
lulase hydrolysis rate and the tensile strength loss has been studied by Shin
et al. (2000). Fabric samples which had been alkalised under tension were
found to exhibit a smaller loss of tensile strength for the same weight loss
compared with control samples, this was attributed to the more uniform
enzyme reaction. Shin et al. (2000) also studied the progress of enzymatic
hydrolysis by scanning electron microscopy. As the enzymatic hydrolysis
progressed, fibrils were produced and damage occurred deep inside the

fibre. The higher crystallinity, moisture regain and dye adsorption of NaOH
pretreated fabrics undergoing the same cellulose treatment conditions can
be explained by the extraction of short molecular chains from the amor-
phous regions, and by change of the amorphous regions into more open
structures.
Similar changes in fibre morphology owing to swelling processes were

also shown for cotton fibres, where a distinct increase in the cellulose hydro-
lysis rate could be observed after various treatments in alkaline swelling
agents (Nicolai and Nechwatal, 2002). Treatment of cotton fabric in 25%
(w/w) aqueous solution of NH 3 , in liquid NH 3 at −40 °C, in 2% (w/w) NaOH
−1
solution at 100 °C and 300 g l NaOH at 20 °C, all led to an increase in the
enzyme hydrolysis rate. Remarkably, almost up to twice the hydrolysis rate
was observed for samples that were not dried after the swelling treatment
and were used for the cellulose hydrolysis in the wet state. When the
samples were dried after the treatments in swelling solution and used as
dry samples for the hydrolysis, the activity of the cellulases was still 10–40%
higher than for untreated materials.

The treatment of cellulose fibres in swelling solutions leads to a substan-

tial change in fibre reactivity and accessibility, similar to the ‘never dried
state’ of freshly spun regenerated cellulose fibres before their fi rst drying.

During drying, the swollen expanded structure of the fibres collapses and,

as a result, the hydrolysis rate decreases.

Compared with cotton fibres, the regenerated cellulose fibres show more
swelling in water and alkaline swelling agents. Thus, the effects of alkali
pretreatment on the hydrolysis rate of cellulases are even more pronounced
than for cotton. In an extensive experimental study, Schimper et al. (2009)
investigated the influence of alkali pretreatment on the hydrolysis rate of

viscose fabric. In addition to the influence of alkali concentration, the effects
of intermediate drying were also studied. Figure 13.5 shows the infl uence
of alkali concentration on the hydrolysis rate observed during the fi rst

© Woodhead Publishing Limited, 2010