DuPont
Plastic is commonly used in the composition of various everyday items. Though
many of these items are recyclable (such as plastic water bottles and fruit containers) a
great deal are not (such as disposable cameras and take out containers). Plastic—both
recyclable and not—is still thrown away. Plastics constitute a significant portion of the
garbage that ends up in landfills and is also 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).
Dependency on nonrenewable resources is risky, due to the danger of depletion. 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. These traditional plastics can take about a thousand years to degrade—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 like what?. 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) has considerably improved the thermal properties compared 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 than what?. The biodegradability of nanocomposites, in
comparison to neat PHB, also increased (Maiti et al., 2007). In addition to the concern
over preserving the strength of traditional plastics, PHB is also 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 a nuisance odor. 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, teen Daniel Burd was featured in the news for having discovered two strains of
microbes that could quickly (in a matter of weeks) compost powdered plastic bags.
(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.
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.
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Didn’t read all. Yejin7