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Hydrolysis of regenerated cellulose fi bres for textiles 321

Determination of the protein concentration in solution did not show a
correlation between the adsorbed protein and total hydrolysis rate. When
the hydrolysis experiment was performed after a dry heat treatment, an

increase in cellulase hydrolysis rate was observed for all fibres at 100–130 °C.
For a 45 s steam treatment at 100–130 °C, a remarkable increase in hydro-

lysis rate appears for all fibres tested. The thermal treatment, particularly
steaming, thus causes an activation of the cellulose surface. At higher tem-
peratures, e.g. 160–190 °C, dry heat treatment leads to a deactivation of the

fibre surface, a phenomenon often called ‘hornification’. Similar results

were obtained with steaming processes between 160 and 190 °C, as super-
heated steam also acts mainly as a drying medium and thus induces horni-

fication of the fibre similar to that with hot air treatment.
13.6 Treatment in alkaline swelling solutions

Treatment in swelling solutions, e.g. alkalisation processes, leads to an inten-
sive reorganisation and activation of the cellulose (Klemm et al., 1998). In

mercerisation of cotton fibres, in addition to reorganisation of the fi bre,
there is also a change in the cellulose crystalline structure from cellulose I
to cellulose II structure. In addition to the effects of alkali concentration,
the amount of applied tension affected the overall activity during cellulase
hydrolysis. Buschle-Diller and Zeronian (1994) compared the infl uence of
slack mercerisation and mercerisation with tension on weight loss and
tensile strength loss during enzymatic hydrolysis of cotton. Cellulase hydro-
lysis occurred at the highest rate in slack mercerised fabric, followed by in
tension mercerised fabric. Alkalisation as a whole activates the cellulose
fibres for enzymatic hydrolysis, which is attributed to higher accessibility

and decreased crystallinity of the fibres after slack mercerisation.

Regenerated cellulose fibres show even higher sensitivity towards reor-
ganisation in concentrated alkali solutions, and at certain concentrations

even dissolution of the fibre can occur. Viscose fibres exhibit a solubility
maximum at approximately 10% (w/w) NaOH solution, and high swelling
in alkaline solution. Modal and lyocell-type fibres exhibit higher stability

against alkali treatment and thus modal fibres can be mercerised in blends
with cotton. Alkalisation of regenerated cellulose fibres can be used to

improve dimensional stability, dyeability, fibrillation and pilling behaviour,
lustre and smoothness (Bui et al., 2008a; Siroky et al., 2009). The alkalisation
process changes accessibility, porosity and sorptive properties for moisture,
elemental iodine and dyestuff (Bui et al., 2008b). These modifi cations are
dependent both on the type of alkali used and the concentration applied.
Alkalisation of lyocell fi bres influences the rate of access and distribution

of a fluorescent whitening agent (FWA) through the cross-section of lyocell

and modal fibres. After alkalization, higher penetration depth and higher

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