Journal of Film Preservation - FIAF

Figure 8: Multi-enzymatic system of cellulases 17
The biodegradation of cellulose triacetate by cellulases requires a
previous attack by esterases in order to reduce the degree of
acetylation by converting the triacetate to segments of a cellulose-like
structure. These resulting structures, containing hydroxyl groups, can
then be degraded by cellulases.
Cellulases act at different positions of the cellulose structure and can
be considered as a multi-enzymatic system. An example is shown In
figure 8 illustrating the biodegradation steps of C1 / Cx / β-glycosidase.
First, cellulose is activated by C1 , then the reactive cellulose is
hydrolysed by Cx to cellobiose structures. Finally, this disaccharide is
degraded by b-glycosidase to glucose units. The biodegradation process
of the cellulose triacetate gives low molecular weight products. Many
micro-organisms10 have cellulases and can act in this way, i.e.
Tricoderma. Penicilium, Fusarium and Aspergillus.
Different authors have reported the influence the degree of acetylation
has on the biodegradation of cellulose acetates by micro-organisms.
The micro-organisms employed in these in papers come from various
sources, and all the results show that the biodegradation is highly
dependent on the degree of substitution by acetates groups.
Experiments made by various authors have demonstrated that the rate
of biodegradation is higher as the degree of acetylation of the cellulose
decreases.
Buchanan18 and co-workers (Eastman Kodak Co) have evaluated the
biodegradation potential of cellulose acetates varying in the degree of
acetylation in two separate assay systems: an in vitro enrichment
cultivation technique, and a system where cellulose acetate films were
suspended in a waste-water treatment system. The waste-water
treatment assay was less active than the in vitro enrichment systems.
The in vitro experiments were carried out employing cellulose acetates
with acetylation substitutions of 1.7 and 2.5. The cellulose acetate with
substitution of 1.7 required 4-5 days to be degraded a 80%, while the
material with degree of substitution of 2.5 required 10-12 days to reach
the same degradation level. When the experiment was carried out with
a cellulose triacetate, no biodegradation was detected after 28 days.
Komarek19 and co-workers have measured the biodegradation
potential of cellulose acetates through the conversion of cellulose
45 Journal of Film Preservation / 67 / 2004