Journal of Film Preservation - FIAF

acetate esters using carbonyl carbon labelled with 14 C to 14 CO 2 . These
experiments were used to evaluate the hydrolytic mechanism of
naturally occurring esterases and the de-acetylation products. In figure
9, the biodegradation of cellulose acetates (DS 1.85, 2.07, and 2.57) is
indicated by the percentage of labelled carbon metabolised to 14 CO 2 by
the mixed microbial population is shown.
Figure 9: Biodegradation of cellulose acetates with different degree of acetylation 19
The conversion to CO2 confirms the biodegradability of these polymers,
but at different rates. The cellulose acetate with the lowest degree of
substitution, 1.85, was rapidly degraded, and within 14 days over 80% of
the polymeric carbon was converted to 14CO2. In contrast the
biodegradation of cellulose acetate with degree of substitution 2..57
was degraded by only 40%. Such results confirm the influence that the
degree of acetylation has on the biodegradation rate of cellulose
acetates.
Samios20 el al. have study the biodegradation of cellulose acetates by a
common soil species, the fungus Aspergillus fumigatus, by inoculating
garden soil on nutrient agar plates containing 1% of cellulose acetates
with varying degrees of substitution between 0.7 and 2.5. These
authors have observed using 13C-NMR that the hydrolysis of cellulose
acetates starts at the carbon at position 6 corresponding to an ester
group, as shown in figure 10. In the materials with highest degrees of
substitution, the ester in carbon 2 is the second to be attacked and the
ester in position 3, the third. When hydrolysis of the ester groups by
esterases takes place molecules of acetic acid are produced.
When the de-acetylation process increases and the degree of
acetylation drops below a certain level, cellulases can attack because
the polymer structure contains units without ester groups and the
typical cellulose biodegradation mechanism mentioned previously can
take place. Cellulases act breaking the glycosidic bond (-O-) and a
46 Journal of Film Preservation / 67 / 2004