Surface Modification of Cellulose Acetate with Cutinase and ...

Subchapter 2.5
treatment medium of CTA. Compared to previous results, the levels of acetic acid are
lower than the observed for the same esterase activity per weight of the substrate.
The diffuse reflectance (DRIFT) technique was used to collect the infrared spectra of
CDA and CTA fabric samples and respective controls in order to obtain further
evidence of the hydrolysis of the ester linkage at the surface of treated fibres. This
technique allows examining the IR absorption by rough surfaces. Figure 4 shows the IR
spectra in the region of 1800-1720 cm -1 which is the wavenumber region for the
stretching vibration of the carbonyl group (Krasovskii et al., 1996).
For CTA (figure. 4B) there was a clear difference in both the intensity and shape of the
carbonyl stretching band between the treated sample and the control. There was a
decrease in the intensity after the cutinase treatment and there was also a shift of the
band to lower wavenumbers. The decrease in the intensity was correlated to the
enzymatic hydrolysis of some ester linkages at the surface of the samples. The
displacement could be caused by the formation of intermolecular hydrogen bridges
between the remaining carbonyl groups and the newly formed hydroxyl groups (Ilharco
and Barros, 2000) or it could be due to a preferential hydrolysis of the carbonyl groups
at C2 e C3 positions (Krasovskii et al., 1996). Regarding CDA (figure. 4A), the observed
differences between the control and sample were considered not significant. The
absence of a significant difference was unexpected because in the treatment liquor it
was possible to detect acetic acid while for CTA it was not.
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