J Polym Environ
Table 1 Global production of cellulose acetate-based products
Cellulose diacetate
materials
Degree of
substitution
(DS)
2008 Global
production
(metric tons)
Coatings, plastics and films
2.5
Textile fiber
2.5
49,000
Filter tow
LCDs, photo films, and textiles
2.5
3.0
690,000
41,000
41,000
Source Chemical Economics Handbook (CEH) Marketing Report
Initially the assessments of the biodegradability of CA
reached the incorrect conclusion that the polymer is not
biodegradable, due to evaluations being performed only
with cellulose degrading organisms like fungi [3]. Later the
importance of the deacetylation step was shown, when it
was learned that acetyl esterase enzymes are common in
microorganisms. Currently CA is generally recognized as a
biodegradable polymer within the scientific community [4–
8]. Recent work has allowed a considerable increase in the
knowledge of the enzymology of non-substituted and
acetylated polysaccharides, thus illuminating the biodegradation mechanism.
Photo degradation is another common mechanism for
many polymers. Although CA polymer alone has limited
photo degradation in sunlight, many consumer products
have additives that allow enhanced photo degradation.
Titanium dioxide is commonly added to enhance the
whiteness of CA materials, and is a photo oxidation catalyst that causes degradation in sunlight.
The final section of this review will cover design
approaches that propose to further enhance the degradation
mechanisms. Research has shown that the combination of
both bio and photo degradation allows a synergism that
improves the overall degradation rate. This synergy is a
result of photo degradation causing pitting and thereby
increasing the material’s surface area, and enhancing biodegradation. Research has shown that the environmental
conditions have a strong impact on a material ’s degradation
rate. The patent literature contains many ideas disclosed for
making consumer products which can be designed to
optimize the degradation environment. A review of key
patent disclosures will illustrate highlights of this diversity
of ideas for enhancing degradation rates.
This paper will review each topic and bring together the
subject, allowing a more complete understanding of the
ultimate environmental impact of CA based products.
Biological Degradation
The early research into the biodegradation of CA polymer
produced some conflicting conclusions. Some researchers
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reported that natural organisms could not degrade CA with
a DS of greater than 1.5 [3, 9], while other researchers
determined that CA with DS of 2.5 had limited utility due
to its degradation [10, 11]. Later experiments identified that
the key mechanism for degradation is an initial deacetylation step by chemical hydrolysis and acetylesterases,
thereby allowing the degradation of the cellulose backbone
with cellulase [12]. In hindsight, perhaps it is self-evident
that the mechanisms for biodegradation should be different
for cellulose versus CA polymers.
In 1957 Reese published the first study on the biological
degradation of various cellulose derivatives and concluded
that just one acetyl per glucose was sufficient to ensure
resistance to degradation by cellulase enzymes [9]. There
was no deacetylation step in this study. In 1972 EPA
Report No EPA-R2-72-046 was published investigating the
biodegradability of packaging plastics. The study consisted
of exposing the polymers to fungi using ASTM Method D1924-63 and judged the growth rates after exposure times
of up to 3 weeks [3]. Under these limited test conditions,
the authors reached the conclusion that CA is not
biodegradable.
Biodegradation was shown in early investigations,
where CA-based reverse osmosis membranes of DS 2.5
were incubated with a variety of microorganisms [11].
Some sources of microorganisms were more successful in
attacking the CA membranes than others. After 2 months
of incubation some CA samples lost their semi-permeability with up to 50% loss of acetyl groups.
It is noteworthy that there has been some debate about
the definition of biodegradation. One view is that biodegradation is defined as microbial initiated conversion of a
substrate in a biologically active environment into carbon
dioxide (aerobically), methane (anaerobically), cell wall
material, and other biological products. Another view is a
requirement of a certain rate of degradation, such as weight
loss versus time.
One novel study was the findings by forensic science
researchers Northrop and Rowe in 1987, who studied the
effect of the soil environment on the biodeterioration of
man-made textiles [13]. They found that cellulose acetate
fibers were significantly deteriorated after 2 months in
moist soil and were completely destroyed after
4–9 months. In this study, the other synthetic textile fibers
(nylon, polyester and acrylics) showed no significant
changes at the end of the 12 month study.
Since these early mixed results, several studies have
confirmed that CA is indeed biodegraded in a natural
environment as measured by a variety of methods. One of
the more convincing degradation studies was the aerobic
biodegradation of radiolabelled CA by Komarek, Gardner,
and Buchanan where they monitored the evolution of CO2
from in vitro samples with the acetyl carbons labeled with