Page 343 - Advances in Textile Biotechnology

324 Advances in textile biotechnology

Table 13.3 Enzymatic hydrolysis of pre-alkalised viscose fibres. Weight loss (%)
after 4 h treatment for different concentrations of NaOH solution (duration of
treatment 1 min) and drying methods (wet = hydrolysis without drying)
(Schimper et al., 2009)
Control NaOH concentration

1.0 mol l −1 2.2 mol l −1 3.5 mol l −1
Wet 32.1 55.2 81.5
Line dried 24.9 26.1 43.3 52.9
Freeze dried 23.6 43.2 46.9

13.7 Technical processing
The strong activation of viscose fibres at higher NaOH concentration is

accompanied by a considerable change in fi bre properties e.g. stiffness and
tensile strength/elongation behaviour, which limits the maximum NaOH
concentration for textile processing to values below the swelling maximum.
In the production of special embroidery, polyester yarn is embroidered
on felt or fabric woven from another material, e.g. polyvinylacohol (PVA),
cellulose acetate or cellulose fi bres, which can be removed in a subsequent
treatment step. PVA can be removed by dissolution in water, cellulose

acetate is dissolved in acetone, and cellulose fibres are removed by acid

hydrolysis. Dissolution of cellulosic fibres e.g. viscose by cellulase hydroly-
sis has been proposed as an alternative green process (Döbel, 1999).
However, for intensive activation of viscose fibres to achieve complete

removal from viscose–polyester blends with enzymatic hydrolysis, concen-
trations above the swelling limit are favourable (Schimper et al., 2008;
Vasconcelos and Cavaco-Paulo, 2006).
In a special variation of the two-step process, the activation agent is

applied only superficially, e.g. by spraying or printing, thus permitting a
localised activation on the surface of a textile. Such effects are of interest
to generate surface modifications during garment washing in ring-dyed

denim (Schimper et al., 2007).

13.8 Conclusion
Man-made cellulose fibres offer great potential future for applications

because they are based on natural resources, which can be processed to give

a very wide range of different fibres. In viscose, modal and lyocell fi bres, the
cellulose polymer shows high chemical reactivity, water sorption and acces-
sibility for lower molecular weight chemicals. During treatment with swell-
ing agents, including water, fibre reorganisation in intercrystalline regions

© Woodhead Publishing Limited, 2010