Page 68 - Advances in Textile Biotechnology

Developments in enzymatic textile treatments 47

1.0
Enzyme concentration, E 0.6
0.8

0.4
0.2

0.0
0 20 40 60 80 100
Time (s)
2.11 The results of model calculations using equation [2.26].

Furthermore, it has been assumed that the convective transfer coeffi cient
is 100 times the stagnant transfer coefficient. The calculations have been

done for five different values of the squeezing factor α as indicated in

Fig. 2.11. These model calculations confirm that the squeezing factor

has a determining effect on the rate with which enzymes are transferred
from a padding bath to the fabric.

2.6 Adsorption limitation in textile pores

Another problem in enzymatic textile treatment processes results from the
relatively high ratio of the surface area and the volume of the capillaries in
the fabric. The enzymes in the capillary liquid adsorb at the capillary surface
until an adsorption–desorption equilibrium is achieved between the surface
enzyme concentration at the surface and the concentration in the capillary
liquid. This adsorption–desorption equilibrium reads:

⎯⎯⎯
→
+
k ads
⎯
SE ←⎯⎯ ES [2.31]
k des
where S is the number of sites at a substrate surface at which enzymes can
be adsorbed, E is the enzyme concentration in the liquid, ES is the surface
concentration of enzymes adsorbed at the surface, and k ads and k des are the
adsorption rate constant and the desorption rate constant. To make the
problem of suboptimal adsorption tangible, the next calculation example
may be helpful. For a capillary in a fabric, filled with a solution of the

enzyme pectinase, the characteristic properties of the capillary and the
enzyme are:
• capillary length, L cap = 0.1 mm, i.e. the thickness of a yarn
• capillary diameter, d cap = 2 μm, the intra-yarn pores
• molecular weight of pectinase, M E = 50 kD = 50 kg mol −1

© Woodhead Publishing Limited, 2010