Journal of Film Preservation - FIAF

Los pocos datos encontrados en la
bibliografía apoyan la hipótesis que
las películas son particularmente
sensibles a la contaminación por
bacterias y hongos, sobre todo cuando
estos materiales se conservan en
condiciones que favorecen la
proliferación microbiana.
Las condiciones de
preservación adecuadas y
exámenes periódicos
preventivos de los materiales
de colección reducirán los
riesgos de deterioro
microbiano de las películas
cinematográficas, concluyen
los autores.
homogeneous medium and carried out slowly, products with different
degrees of substitution can be obtained. The cinematographic
triacetate grade usually has 2.7% of acetylation degree.
The cellulose triacetate structure is shown in figure 7.
Fig. 7. Chemical structure of cellulose triacetate (Ac ∫ -COCH3)
Such material exhibits a high rigidity and for the cinematographic films
different plasticisers are added, such us triphenylphosphate, at 12-14% 1
of the polymer weight. Hence, plastic materials can be obtained with
suitable mechanical properties to produce flexible cinematographic
supports of 130-140 micrometers in thickness. This film is obtained from
a highly viscous solution of the polymer, plasticiser and other additives
in methanol, methylene dichloride and n-butanol as solvent mixture.
The viscous mixture cast onto an endless conveyor belt on which the
material is dried. After that, the different photographic layers (fig. 1) are
coated.
Cellulose triacetate can suffer de-acetylation by the principal effects of
temperature and moisture. A product of these reactions is the release of
acetic acid, which in its turn, acts as a catalyst of the reaction. The
presence of the acetic acid is easily recognisable by the vinegar smell
that the degraded films1-5 give off, which is why this effect has been
called “vinegar syndrome”.
Cellulose triacetate is made by chemical modification of cellulose, the
most abundant organic compound in nature, and the principal
component of plant cell walls. Cellulose17 is a natural renewable
resource that can be degraded by many micro-organisms in the
environment.
The biodegradation of compounds is normally carried out by microorganism
possessing enzymes capable of the conversion of chemical
structures to organic products that they can use as carbon source. In this
context enzymes are proteins which are able to biodegrade different
materials, and cellulose acetates are efficiently degraded by both
esterases and cellulases. Cellulose acetate is an important organic ester
because of its broad applications in the producton of fibres, membranes,
plastics and films.
Esterases catalyse the chemical hydrolysis of esters, while the cellulases
act by hydrolysing the overall cellulose structure. There are a variety of
cellulases since cellulose is a very complex substrate and can be attacked
at different bonds of the macro-molecule.
44 Journal of Film Preservation / 67 / 2004