Page 127 - Advances in Textile Biotechnology

108 Advances in textile biotechnology

differences are diluted and the sensitivity of the method is weakened if the
chosen analytical method takes into account both the bulk and the surface
of the tested material.
Nowadays, there are numerous analytical techniques available to study
the surface of materials (Niemantsverdriet, 2007). The spectroscopic

methods most used for the evaluation of chemical modifications in textile
materials are Fourier transform infrared spectroscopy (FTIR) and x-ray
photoelectron spectroscopy (XPS)/electron spectroscopy for chemical anal-

ysis (ESCA). FTIR provides specific information about chemical bonding.
When analysing the surface, FTIR is used coupled to the attenuated total

reflectance (ATR) technique or as diffuse reflectance infrared Fourier
transform (DRIFT). XPS/ESCA is used to determine quantitative atomic
composition; it is a surface analysis technique with a sampling volume that
extends from the surface to a depth of approximately 50–70 Å.
Knowing the chemical groups generated during biocatalysis on the

surface of the fibres, it is possible to have a relative quantifi cation using
dyes that specifically react with them. When the PAN is treated with nitrilase,

the formation of carboxylic groups can be evaluated by staining the fabric
with a basic dye, which has a cationic group able to establish ionic bonds
with anionic groups on the fibre. Similarly, when PAN is treated with nitrile

hydratase, the formation of amide groups at the surface of the fibres can be
evaluated by staining the fabric with an acid dye. Staining both controls and
samples in the same dyeing bath (competitive assay) allows the increase in
those particular chemical groups to be estimated as more dye can be
absorbed into the biomodifi ed fibre (seen as an increase in colour). The

differences in colour strength are measured as K/S (the ratio between
absorption K and scattering S) at the maximum absorption wavelength of
the particular dye, a parameter proportional to the dye concentration in the

fibre comparing the enzyme-treated and control samples (Kuehni, 1997).
This staining methodology is a valuable and a very sensitive semiquantita-
tive method because of the large molar absortivities of dye molecules
(Matamá et al., 2006, 2007; O’Neill et al., 2007; Silva et al., 2005).
The hydroxyl groups that result from the enzymatic hydrolysis of cellu-
lose acetate can be evaluated using another class of dyes, the cotton reactive
dyes, in particular, the warm brand vinylsulphone dyes. These dyes are able
to covalently link to the hydroxyl group at low temperatures and relatively
low alkaline pH, and the elimination of the protective group does not

depend on the fibre to be dyed (Hunter and Renfrew, 1999). The moderate
temperatures (below the glass transition temperature) are important to
restrict the staining to the surface, stressing the differences between modi-

fied samples and controls (Burkinshaw, 1995). The pH is important in the
particular case of cellulose acetate because this material is not chemically
stable at high pH because of the chemical hydrolysis of the acetyl groups.

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