DuPont
Plastic is commonly used in the composition of various everyday items. Though
many of these items such as plastic water bottles and fruit containers are recyclable, a
great deal, such as disposable cameras and take out containers, is not. Plasticis still
thrown away and thus constitutes a significant portion of the garbage that ends up in
landfillsas a large contributor to water pollution. Furthermore, international dependence
on fossil fuels for plastic production alone results about 270 million metric tons (waiting
on clearer information; Khardenavis et al, 2006). Due to the danger of depletion,
dependency on nonrenewable resources is risky. The actual manufacture calls for
chemical manipulation and the resulting product may still give off unsafe chemicals. All
in all, traditional plastics can be devastating to the environment b/c they can take about a
thousand years to degradeThis is a dangerously unbalanced figure in comparison to the
rate at which we produce and consume plastics (waiting on reference). However, there
are some plastics that are designed to degrade. Whereas once, experiments and studies
were directed towards strengthening plastics and lessening deterioration, now they are
aimed at developing ways to better degrade plastics (Leonas & Gorden, 1995). The most
commonly used and studied degradable plastic is polyhydroxybutyrate (PHB)
(Khardenavis et al., 2006). It is important to find more efficient ways to produce and
eliminate plastic in order to minimize their negative impact on the environment.
In the past, the use of biodegradable plastics has been discouraged by high
production costs and inferior physical properties. However, experiments have been
conducted to improve these qualities (Maiti et al., 2007; Khardenavis et al., 2006). It has
been found that PHB nanocomposites (plastic implanted with nanosized clay particles)
have considerably improved the thermal properties as opposed to neat PHB (the
unmodified polymer). The nanocomposites typically withstand more heat than neat PHB.
For example, one type of nanocomposite, PHB, with 3.6% clay by weight, held together
for about 30°C greater. The biodegradability of nanocomposites, in comparison to neat
PHB, has also increased (Maiti et al., 2007). In addition to the concern over preserving
the strength of traditional plastics, PHB has also become less desirable to manufacture
due to the necessity of expensive carbon sources in sustaining the bacteria that produce it.
In an attempt to lower the production costs of PHB, wastewaters from the dairy and food
processing industries,which already contain both the carbon and the necessary
microorganisms,were evaluated for their ability to produce it. The tests resulted
favorably, and it was concluded that using wastewater is viably a cheaper alternative of
producing PHB. The most effective of the wastewaters tested was the rice grain based
distillery spentwash (unwanted residual waste from rice processing), which yielded 67%
PHB (Khardenavis et al., 2006).
An assessment of biodegradation finds nanocomposites and poly-caprolactone
(PCL) to be particularly effective (Maiti et al., 2007; Nakasaki et al., 2000). The
nanocomposites biodegraded relatively quickly. In room temperature, one type of
nanocomposite had almost completely broken down in about seven weeks, whereas the
neat PHB had degraded only about 70% (measured by weight loss) after eight weeks.
Under 60°C, the nanocomposite and the neat PHB reached the 30% biodegradation mark
at six and nine weeks respectively. It significantly outperformed the neat PHB in both
room temperature and 60°C heat (Maiti et al., 2007). The PCL, on the other hand, was
useful in reducing ammonia emission during compost. During compost, PCL releases an
acid that neutralizes ammonia. This is important because the acid is costly; some
composting facilities in Japan have washed their ammonia with acid, but the cost of
doing so has triggered the process to be almost completely abandoned. Furthermore,
ammonia is an olfactory nuisance. Reduction of ammonia during composting could
encourage the composting of both organic waste and biodegradable plastics (Nakasaki et
al., 2000). This increases the potential of composting, for example, in residential
neighborhoods that might have previously forbade compost due to the odor. In general,
biodegradable plastics are helpful to our environment simply because they are
compostable. Compost is important because it reduces the amount of garbage taking up
space in landfills, and on a larger scale, on earth (Song et al., 2009). There is only so
much space on our planet.
Other studies have also been conducted to improve the elimination process of
plastics. Plastics break down in one of two ways: biodegradation or photodegradation.
Biodegradation indicates decomposition of bacteria. As of 1995, no especially effective
strains (for degradation in water) could be found (Leonas & Gorden, 1995). However, in
2008, (teenDaniel Burd was featured in the news unnecessary information. Who cares?)
for having discovered two strains of microbes that could compost powdered plastic bags
in a matter of weeks.
(Waiting for photodegradation information and additional
biodegradation information.)
Developments in plastic technology have brought increasing potential for a
greener earth. Landfill reduction, material recovery, decreasing dependency on
nonrenewable resources, and pollution reduction are only some of the aspects that could
be affected (Song et al., 2009). (Awareness, however, of the enormous impact humans
have on their environment is the first step in achieving this. Out of line, random.)
Mostly o.k. Not sure if it flows smoothly enough.
References: (Note--waiting on 1, 6, 8, 9)
Ishigaki, T., Sugano, W., Nakanishi, A., Ike, M., & Fujita, M. (2004). The degradablility
of biodegradable plastics in aerobic and anaerobic waste landfill model reactors.
Chemosphere, 54, 225-233.
Khardenavis, A.A., Kumar, M.S., Mudliar, S.N., & Chakrabarti, T. (2007).
Biotechnological conversion of agro-industrial wastewaters into biodegradable
plastic, poly hydroxybutyrate. Bioresource Technology, 98, 3579-3584.
Leonas, K.K., & Gorden, R.W., (1996). Bacteria associated with disintegrating plastic
films under simulated aquatic environments. Bulletin of Environmental
Contamination and Toxicology, 56, 948-955.
Maiti, P., Batt, C.A., & Giannelis, E.P. (2007). New biodegradable
polyhydroxybutyrate/layered silicate nanocomposits. Biomacromolecules, 8,
3393-3400.
Nakasaki, K., Ohtaki, A., & Takano, H. (2000). Biodegradable plastic reduces ammonia
emission during composting. Polymer Degradation and Stability, 70, 185-188.
Shah, A.A., Hasan, F., Hameed, A., & Ahmed, S. (2008). Biological degradation of
plastics: A comprehensive review. Biotechnological Advances, 26, 246-265.
Song, J. H., Murphy, R. J., Narayan, R., & Davies G. B. H. (2009). Biodegradable and
compostable alternatives to conventional plastics. Philosophical Transactions of
the Royal Society B, 364, 2127-2139.
Yang, H.S., Yoon, J.S., & Kim, M.N. (2004). Effects of storage of a mature compost on
its potential for biodegradation of plastics. Polymer Degradation and Stability,
84, 411-417.
Zheng, Y., Yanful, E.K., & Bassi, A.S. (2005). A review of plastic waste biodegradation.
Critical Reviews in Biotechnology, 25, 243-250.