Conference Section A13
#2311
BIO-PLASTICS: AN ECONOMIC AND ENVIRONMENTAL CHOICE
Alexander Horn agh24@pitt.edu, Nick Sumoski nas152@pitt.edu
Abstract—Bio-plastics are biologically based plastics,
which mean they are made from organic material such as
corn and other types of plant life [1]. Therefore they are
biodegradable, which makes them resources humans can
consume that are less harmful to the environment.
Bio-plastics pose several advantages over traditional
petroleum-based plastics, such as decreasing production of
CO2, a greenhouse gas, as well as reducing costs and
dependence on imported petroleum [2].
Currently the two most promising bio-plastics are
polylactic acid (PLA) and polyhydroxyalkanoate (PHA).
PLA, is only 20% more expensive than petroleum-based
plastics (compared to PHA which is almost twice the cost),
and is almost indistinguishable in appearances from regular
petroleum-based plastics [1].
The objective of this paper is to analyze the various
production methods of engineering bio-plastics, to clear the
confusion the public has about the definition of Bio-plastics
and how it is different from other renewable and traditional
plastics. The paper will compare the benefits—
environmental and economic—of using biologically-based
materials for the production of plastics to the currently used
petroleum-based
plastics.
the price of petroleum increases, this will drive up the price
for plastics since they are composed of petroleum [4]. In an
attempt to keep plastics a cheap alternative to other
materials, an alternative to petroleum-based plastics must be
found that is independent of the unpredictable nature of the
oil industry.
Two environmental concerns heralded by scientists and
environmentalists all over the world are to reduce the
amount of CO2 that human activities release into the
atmosphere and to reduce the amount of plastic that is being
put into landfills [4]. Regardless of the cause of this
movement, bio-plastics have emerged as a potential
candidate for solving some of the many problems that plague
our modern world.
In this paper, the various methods of reducing the
consumption of petroleum-based plastics will be discussed
along with a comparison of these methods with traditional
plastics. The various production methods of engineering
bio-plastics will also be examined in addition to the
environmental advantages and concerns of using bioplastics.
WHAT IS A BIO-PLASTIC AND WHAT MAKES IT
DIFFERENT?
Key Words— Bioplastics, biologically based plastics, green
technology, PLA, PHA.
Given the concerns surrounding plastics in landfills and the
consumption of petroleum, many alternatives have
developed in response to these problems. One such
alternative is Recycled plastic which takes previously used
plastic and either combines it with virgin materials or other
recycled plastics [3]. While there is a process that allows a
plastic to be reused in plastic bottles, this process is much
more difficult than most people realize and technology is
only now being developed to allow such a process to occur.
Once the initial raw material for plastic is melted, it
undergoes a chemical reaction, so that if the plastic is melted
again, it will not have the same properties it once had; this
generally means a significant loss of strength of the material.
As a result, the large majority of recycled plastic get melted
down and transformed into low-grade plastics for use in
benches, decks, playgrounds, and even insulation. While
recycling plastic does not provide the benefit of reducing our
consumption of virgin plastic, it does prevent plastic from
ending up in a landfill.
Another environmentally friendly option for plastic is a
class of plastics that are biodegradable and can be made of
either petroleum or biological material [3]. Petroleum-based
biodegradable plastics are good since they only require
additives in order to become biodegradable. This minimal
requirement means that this particular type of plastic is a
BIO-PLASTICS: FOR A MORE
ENVIRONMENTALLY FRIENDLY WORLD
Plastics are key materials in manufacturing the day-to-day
items we use, from containers and bowls to chairs and
tables. Indeed, manufacturers use plastics to create much of
what we use on a daily basis, yet most people still do not
know what materials plastics are made from. Plastics are
carbon polymers—polymers are long chains of molecules
that repeat their structure throughout the chain—most
commonly constructed from petroleum, which is the most
natural form of traditional plastics before it is processed into
what most people know as a plastic [3]. Petroleum is the
form of oil taken directly from the ground (commonly called
crude oil), and because petroleum is a non-renewable fossil
fuel, humans will eventually consume all of it while
polluting the environment.
In the past decade there has been an increasing push
towards alternative methods for creating plastics using
renewable materials stemming from both economic and
environmental concerns. The economic concerns increase as
the price of petroleum consistently increases with expanding
global oil consumption and declining oil reservoir levels. As
University of Pittsburgh
Swanson School of Engineering
February 7, 2012
1
Alexander Horn
Nick Sumoski
14
good hybrid of plastic technology since the strength of
traditional plastics is maintained while having the advantage
of biodegradability. This is certainly a good option until a
suitable bio-plastic is developed to be both cheap and
sufficiently strong. While petroleum-based plastics certainly
have advantages, they still rely on petroleum and do not
have the potential of bio-plastics.
The other type of biodegradable plastic is the main focus
of this paper, bio-plastic. This particular type of plastic
meets all the environmental needs since it does not require
petroleum and decomposes in the environment on a much
shorter time scale than regular plastic. Bio-plastics, or
biologically based plastics, are plastics that are composed of
bio-based material.
Bio-based materials are organic
materials in which the carbon comes from a non-fossil
biological source [5]. This is the fundamental difference
between bio-plastics from other renewable plastics such as
biodegradable plastics, eco/recycled plastics, and even
traditional petroleum based plastics which all use carbon
compounds from a fossil source. Based on this definition,
the carbon in the material must come from a source that has
recently been “alive” and therefore hasn’t been able to
fossilize.
In order to figure out whether a product is bio-based or
not, it is necessary to find out how long it has been since the
organic source was “alive”; to do this carbon dating
techniques are used . In carbon dating, scientists follow the
cycle of carbon-14 (14C) a radioactive isomer of carbon12.Since carbon-14 is radioactive, it degrades at a set rate
and the time it takes for a radioactive sample to degrade to
one-half is called the half-life of the sample. After much
research scientists have calculated the half-life of carbon-14
to be around 5730 years so fossil sources will essentially
have no 14C signature since it takes millions of years for
fossils to form [5].
In order to understand how scientists are able to use
carbon-14 to date organic material is it is important to refer
to the figure above. Figure 1 shows the cycle of 14C, it is
formed in the upper atmosphere as a side effect of cosmic
radiation and is then oxidized (a reaction in which oxygen
atoms bond to a central atom) to form 14CO2.
C atoms in them will stay relatively the same due to the
equilibrium of those atoms with the 14C atoms in
atmosphere. However, once the organism dies, they do not
collect anymore 14C atoms and the remaining will decay
without being replenished. Using this decay, scientists are
able to date how long organic material has been dead.
Scientists only then need two more things to find out
how long ago the carbon was in a living organism: 1) they
need to know the original amount of carbon -14 in the source
before it died and 2) the final amount there is in the material
now. For the original amount of 14C, scientists use the
Modern International Radiocarbon Dating Standard Oxalic
Acid I (C2H2O4) [6]. To find the final amount the scientists
need only to analyze the material for the amount of 14C still
contained in it. The American Society for Testing and
Materials (ASTM) subcommittee developed a test method to
quantify the amount of 14C in a product [5].
In this method, the sample is first prepared by
combusting the product in the presence of oxygen to produce
CO2 gas. From here the gas can be analyzed by one of four
different methods to find the amount of bio-based carbon
that is in the product [5].
The first method uses Liquid Scintillation Counting
radiocarbon techniques to find the amount of 14C in a
product; it has a percent error of 5-10% [5]. In this technique
a cocktail is created out of a solvent, emulsifier, and fluor. A
solvent is the liquid that dissolves a compound in a solution;
in this case the cocktail itself is the solvent. The emulsifier
creates the solution by forcing the chemicals to mix. The
fluor is the chemical component in the cocktail that absorbs
UV light emitted by the solvent and then emits a visible blue
light [7-8].
FIGURE 2
LIQUID SCINTILLATION DIAGRAM [7]
When the sample emits beta particles due to radioactive
decay, UV light is released. This light is then absorbed by
the fluor and released as blue light every time it absorbs the
energy of the sample’s radioactive decay. Every time UV
light is released 10 photons are released per 1000 Volts of
energy. The total number of photons (packets of light
energy) released constitutes the scintillation [7]. These
photons hit the photo cathode of the photo multiplier tube.
This releases a number of electrons proportional to the
number of blue light photons. This information is then
FIGURE 1
THE CYCLE OF 14C [5]
This compound then enters the plants through
photosynthesis and the animals that eat the plants.
Throughout the lives of the animals and plants the number of
2
Alexander Horn
Nick Sumoski
analyzed and converted into digital values which can be
plotted in order to show how much radioactive material there
is dissolved [7].
have a different amount of neutrons (denoted by the number
after the dash), they are still both Carbon atoms. The CO2 is
kept within the vacuum and is instead distilled, quantified in
a calibrated volume then transferred to a quartz tube to be
transported to an IRMS facility for the analysis of the
isotopic ratio. The ratio between 14C to 12C is then used to
find the actual concentration of 14C with the use of a 12C
standard measurement [5].
The fourth method uses Liquid Scintillation Counting
just like the first method except, instead of analyzing the
CO2 in a solution, it analyzes a sample of carbon that has
been converted to benzene [5].
Of the types of environmentally friendly plastic
alternatives, bio-plastics clearly have the most potential, but
not all bio-plastics are equal. In the next section, the various
types of bio-plastics will be analyzed with regard to how
they are made, as well as any potential applications the
particular bio-plastic excels at. It is crucial to have a variety
of plastics to meet a variety of needs since no material is
perfect for every application.
FIGURE 3
AMS SYSTEM [9]
The second method uses Accelerator Mass Spectrometry
(AMS) which has a percent error of 1-2%. Figure 3 is a
diagram of a standard AMS system. Figure 3 illustrates a
typical AMS system. The system starts at the ion source
where ions (charged atoms) of the carbon in the CO2 are
created due to an ionizer (a product that changes an element
into a charged ion by removing or giving an electron to it)
and shot out in a stream [9]. The stream is separated into
negative and positive ions, with the negative ions being
directed on to the injector magnet. The injector magnet
bends the stream by 90 degrees toward the tandem
accelerator in order to filter out the heavier isotopes. In the
tandem accelerator the ions are accelerated, by the attractive
forces of a positive magnet, towards an electron stripper
which takes off electrons and makes the ions positive [9].
The positive ions are then accelerated again by the repulsive
forces of another positive magnet towards the analyzing and
switch magnets. The analyzing and switch magnets both
filter out the ions of other carbon isotopes, which leaves only
14
C ions to be sent to electrostatic analyzer [9]. The
electrostatic analyzer filters out the 14C ions that do not have
enough energy to give accurate measurements in the gas
ionization detector. As the ions proceed through the gas
ionization detector, they are counted and the number of 14C
ions is recorded [9].
The third method uses Isotope Ratio Mass Spectrometry
(IRMS) techniques to figure out the amount of bio-based
carbon, these techniques have a percent error of .1-.5%.
IRMS uses the isotope abundances of the various elements
in a sample to find the biological origin of a sample;
however it is only important to note how it finds the
concentration of 14C [10]. Elements are atoms that are the
basic building blocks of everything in the universe; they
cannot be broken down by chemical means and their
properties are defined by the number of protons—positive
sub-atomic particles—they have. An isotope is an element
that has a different number of neutrons (neutral sub-atomic
particles) within the nucleus of an atom. Because the number
of neutrons in an atom does not determine their chemical
properties they are still considered the same element. An
example is Carbon-14 and Carbon-12; even though they
BIO-PLASTICS: THE PROCESS
Traditional plastics are made by taking organic molecules in
the form of petroleum and synthesizing them to undergo
various chemical reactions. In much the same way, bioplastics are the result of biologically based organic
molecules undergoing chemical reactions. Bio-plastics can
be made from materials ranging from plant starches to wood.
In this section, the various types of bio-plastics will be
addressed as well as their production methods [11].
Polylactic acid, or PLA, is one of the major types of bioplastics and is currently being implemented in industry
today. PLA begins as starch, a polysaccharide that plants
use to store their source of energy, glucose. The use of
starch is very advantageous because it is one hundred
percent renewable, removing it from some of the
environmental problems that there are with petroleum [11].
The most commonly used starches are from wheat, corn, and
waste products from the agricultural industry. One specific
example is green juice, a by-product of the production of
animal feed, which has been proven to be a cost-effective
method for producing PLA. Agricultural waste is a very
promising source for bio-plastics since the use of it prevents
the waste from occupying landfills or requiring disposal and
would reduce the need for corn and wheat for non-food
purposes, minimizing any potential food price increase.
This is a very important issue, since like ethanol, replacing
petroleum with plant-based material reduces environmental
impact, but increases food prices since food is being diverted
for other purposes. From here, the glucose is turned into
lactic acid by the process of fermentation [11].
One method of producing PLA begins by purifying the
lactic acid. The process of purification is completed by
dehydrating the Lactic Acid in a vacuum, followed with
3
Alexander Horn
Nick Sumoski
distillation in a vacuum, which gives the distillation product
[12]. Once it is purified, it is mixed with dichlorobenzene
and metallic tin. After the reaction is carried out at 180°C,
the tin is filtered off and the solution is poured into
methanol. The result is a white powder which is washed
with additional methanol and dried at 80°C. This powder is
then synthesized in both p-xylene and o-chloro-toluene
(organic molecules). The resulting product is dissolved in
methanol where PLA is precipitated giving the final product
[12].
While the aforementioned method produces PLA
consistently, another method of PLA production has the
potential to be more useful. This process involves using the
previously mentioned distillation product and adding
metallic tin to it in addition with p-xylene [12]. This
solution is heated to 136°C until the water is removed.
Following this step, diphenylether is added and the solution
is heated to 130°C in a vacuum. The result is PLA, but this
process if favorable to using the previously mentioned
process since there are fewer steps and consequently a lower
cost. One difference between the two methods is the
resulting viscosity of the PLA. The first method should not
be disregarded since a different viscosity could have uses in
other applications where a plastic with slightly different
properties could be useful [12].
There are two enantiomers of Lactic acid that give two
distinct enantiomers of Polylactic Acid upon synthesis. The
term enantiomer is used to describe organic molecules that
have identical chemical formulas but the functional groups
connected to an asymmetrical carbon atom are in a different
order. L-Lactic Acid is naturally occurring and is more
common whereas R-Lactic Acid can only be produced by
microorganisms or by the laboratory process of racemization
[11]. Racemization is the process by which a solution of
only one enantiomer undergoes a reaction so that there is
more than one enantiomer of an organic compound present.
Pure L-PLA makes a crystalline plastic with a high melting
point whereas a mixture of L-PLA and R-PLA makes an
amorphous plastic that would be more moldable.
The existence of PLA in two different enantiomers with
distinct properties allows for a versatile plastic with a variety
of characteristics to meet the needs of various applications.
Another promising bio-plastic is polyhydroxyalkanoate
(PHA). PHA is naturally made by bacteria and is produced
in labs by maintaining optimum pH levels, temperature, and
nutrient supplies. This type of bio-plastic was initially
written off because of its high price of $16 per kilogram in
comparison to petroleum-based plastics which are around
$0.25-$0.50 per kilogram. After refining the process, the
price was reduced to $4 per kilogram [13].
Following this development, engineers made another
advancement, they used genetic engineering to create plants
that undergo the process as the bacteria so they could have
plants produce PHA instead of the costly process of having
bacteria producing it. This reduced the price down to $1 per
kilogram, close to the low cost of starch-based bio-plastics.
This particular bio-plastic is an excellent example of how
devoting engineering resources to an impractical technology
can slowly improve the technology to the point where it
becomes both practical and cost-effective [13].
Polyhydroxybutyrate (PHB) is a type of PHA and is also
produced by bacteria. The majority of bio-plastics are either
water-soluble or moisture sensitive, but PHB is resistant to
both of these making it very suitable to specific applications
where water sensitivity is important [14]. One such example
is in the medical industry where its resistivity to water keeps
the art in the body long enough to serve its purpose while the
nature of the plastic makes it biodegradable so that it
dissolves before it needs to be removed saving the patient
additional surgery [14].
Another type of bio-plastic is Thermoplastic Starch
(TPS). While this material is only partially biodegradable, it
can be combined with various other completely
biodegradable bio-plastics to negate this problem. There is
an increasing trend to find a way to combine TPS with other
bio-plastics because TPS is very cheap to produce in
comparison to the other bio-plastics known [15]. The major
problem for engineering is to develop a process so that these
plastics can be combined while minimizing effects on the
physical qualities of the plastics while maintaining
biodegradability and cost efficiency.
While the majority of the discussed plastics come from
starches, a newly developed bio-plastic, Liquid Wood,
breaks this pattern by using lignin. Wood has three main
components: lignin, cellulose, and hemicellulose [16].
Lignin is a by-product in the process of paper making so the
production of liquid wood requires no harvested materials,
similar to the aforementioned green juice. This provides a
two-fold benefit; the lignin does not require disposal and it
by substituting some petroleum-based plastics with liquid
wood, the world’s petroleum usage could be decreased [16].
The process for making liquid wood is fairly simple
compared to some of the other bio-plastics. This starts with
the separation of lignin from the leftover material that is
accomplished with a sulfur-containing chemical [16].
Liquid wood was previously limited to automobile uses
because of the sulfur content, but because scientists were
able alter the process and reduce the required sulfur by
around ninety percent, the plastics have now been deemed
safe for household use. The separated lignin is then mixed
with a fibrous material such as wood or flax and is then
mixed with natural additives like wax. Once this mixture is
obtained, the liquid wood can be melted and injection
molded just like any other plastic [16].
In the world’s current use of plastic, no sole plastic is
used for all purposes, rather a wide variety of plastics for
various applications and demands in durability, flexibility,
optical, and numerous other qualities. In much the same
way, bio-plastics should not rely on one technology, but
rather the variety of technologies currently offered to meet
the needs of consumers for various applications. Using
specific bio-plastics for specified applications in conjunction
4
Alexander Horn
Nick Sumoski
with the improvements in cost and durability will surely
make bio-plastics a viable option to replace petroleum-based
plastics in the near future.
escalate the cost of food, making it more difficult for people
to be able to purchase enough food. Another drawback is
that when bio-plastics decompose they leave behind harmful
chemicals, from the use of fertilizers and chemicals in the
creation of the renewable raw materials, which strongly
contributes to the acidification of the soil and eutrophication
[4].
ENVIRONMENTAL CONCERNS
There are many ethical issues surrounding bio-plastics and
their potential use in industry because they have benefits as
well as threats to the environment. One of the major
objectives of this paper is to address the many environmental
issues that bio-plastics are involved in. Bio-plastics have
many advantages ranging from reducing petroleum usage to
reducing landfill waste.
As oil consumption increases with each passing day
because of events such as the industrialization of China and
India, it is more important than ever to find renewable ways
to reduce human consumption of fossil fuels. While oil
consumption is generally thought to be through automobiles
and power production, plastics play a large role in our oil
consumption, because its petroleum based, through
disposable plates and cup and almost anything else found in
the typical home. Finding a way to reduce this usage is
crucial for the environment for numerous reasons. One such
reason is that the practice of oil extraction is very costly to
the environment as a direct result of the mining sites and the
oil pipelines that span countless miles.
Along with the extraction of oil, the use of oil carries its
own adverse effects on the environment. The most notable
is the combustion of oil that produces a variety of gases that
are harmful to the environment. Another major issue
involved with the use of petroleum for plastics is that the
majority of plastic ultimately ends up in a landfill [4]. In the
landfills the plastics do not breakdown quickly, it takes
hundreds of years for a plastic to completely breakup and
even then it is possible for the plastic to leave behind
harmful chemicals in the ground [3].
Bio-plastics seek to solve the problem of plastic
occupying landfills since bio-plastics, unlike the majority of
petroleum-based plastics, are biodegradable. This ability to
quickly decompose in the soil means that these plastics
would breakdown in a much shorter time span compared to
its petroleum based counterparts. This could also reduce the
risk of animals ingesting plastic since any litter in the
environment has the slight possibility to decompose before
afflicting any animals.
While bio-plastics are designed to help the environment
and they do this very well, table 1 shows bio-plastics
overwhelmingly outperform petroleum based plastics in
energy conservation and lower greenhouse gas emissions
[4].
However, they do carry several drawbacks as well. One
such concern is that since they are biologically based, the
biological material must come from somewhere, namely
starches found in crops. With a significant percentage of the
nation’s corn already being devoted towards the production
of ethanol, increasing the demand further would only
TABLE 1
ENERGY CONSUMPTION AND CO2 PRODUCTION OF TRADITIONAL PLASTICS
VS. BIO-PLASTICS [4]
The acidification of soil causes the soil’s acidity to
increase significantly because hydrogen (H+) and aluminum
(Al3+) ions replace the natural bases (magnesium, potassium,
and calcium) in the soil [17]. High concentrations of Al3+ in
soil of high acidity are detrimental to plant life because of its
ability to disrupt nutrient uptake due to the destruction of the
plant’s cell walls. High enough concentration can also kill
earthworms in the soil as well as leak into nearby water
systems [17]. Eutrophication is a condition where a body of
water (usually lakes) has too high a concentration of
minerals. This causes an increase of plant growth in the lake
and a decrease in the available oxygen in the lake [18]. As
the oxygen in the lake is depleted, the fish and other
organisms that live in the lake die contributing to polluting
the lake.
Despite this, bio-plastics do pose several advantages over
ethanol as a replacement for petroleum since they offset
more petroleum than ethanol per acre of crops. In addition,
bio-plastics can also be made from the by-products of certain
processes, providing them the benefit of adding no demand
to agricultural resources.
BIO-PLASTICS: PROGRESS TOWARDS A GREEN
FUTURE?
There are many types of bio-plastics, the ones discussed in
this paper (PLA, PHA, PHB, Thermoplastic Starch, and
Liquid Wood) are only some examples of different bioplastics. All of the bio-plastics have their own benefits and
drawbacks.
Currently, bio-plastics are the better option compared to
traditional plastics when considering lowering energy
5
Alexander Horn
Nick Sumoski
bacteria-to-make-bioplastics.htm
[15] Mohini Sain. “Thermoplastic Starch”. BioscienceWorld. [Online].
Available: http://www.bioscienceworld.ca/ThermoplasticStarch
[16] (2009, January). “Liquid Wood Is Plastic of Tomorrow, Say
Scientists.” DW. [Online]. Available:
http://www.dw.de/dw/article/0,,3938912,00.html
[17](11 Oct 2010). “Acidification” . Air Pollution Information System.
APIS.
[Online].
Available:
http://www.apis.ac.uk/overview/issues/overview_acidification.htm
[18] U.S. Department of the Interior. (27 Dec 2011). “Eutrophication”
Toxic
Substances
Hydrology
Program.
[Online]
Available:
http://toxics.usgs.gov/definitions/eutrophication.html
consumption and CO2 production. However there is still the
acidification of the soil and eutrophication problems that
need to be addressed before bio-plastics should be mass
produced for market use. Research is being conducted every
day to reduce the negative aspects of bio-plastics and great
strides have been made towards making them a practical
replacement for traditional plastics.
With each passing year scientists are creating bio-plastics
that have properties which are becoming increasingly similar
to their petroleum-based counterparts. With the rising oil
prices and increasing environmental concerns, it will only be
a matter of time until bio-plastics become not only practical,
but rather become even more economical than traditional
plastics. To expedite this process of adoption, scientific
resources must continue to be devoted to researching and
improving these technologies so that our lives can be
cleaner, safer, as well as less harmful to the environment.
ADDITIONAL REFERENCES
Pr. Luc Averous. (2009). “Bioplastics: Biodegradable polyesters (PLA,
PHA, PCL ...)” Biodegradable Polymer, Biopolymer, Agro-polymer,
Bioplastic, Biomaterial, Compostable Packaging. [Online]. Available:
http://www.biodeg.net/bioplastic.html
Jessica Mershall. (2010). “Bioplastics Not So Green.” Discovery News
[Online].
Available:
http://news.discovery.com/earth/bioplastic-plantplastic-environment.html
“Peter Reineck: Inside Take On Bioplastics.” Society of Chemical Industry
[Online]. Available: http://www.soci.org/News/BioResources-Reineck
Mar Lemos Stein. (2010). “Just One Word:Bioplastics.” The Wall Street
Journal
[Online].
Available:
http://online.wsj.com/article/SB10001424052748703989304575504141785
646492.html
REFERENCES
[1 ] Kristina Dell. (2010, May 3). “The Promise And Pitfalls of Bioplastic.”
Time
Magazine.
[Online].
Available:
http://www.time.com/time/magazine/article/0,9171,1983894,00.html
[2] Nick Heath. (2007, July). “Bio-plastics: Turning Wheat And Potatoes
into
Plastics.”
The
Naked
Scientist.
[Online].
Available:
http://www.thenakedscientists.com/HTML/articles/article/bioplastics/
[3] Chris Woodford. (2011, October 3). “Bioplastics and Biodegradable
Plastics.”
Explain
That
Stuff.
[Online].
Available:
http://www.explainthatstuff.com/bioplastics.html
[4] F. Gironi. (2011, August 9). “Bioplastics and Petroleum-based Plastics:
Strengths and Weaknesses.” Taylor & Francis [Online]. Available:
http://www.tandfonline.com/doi/full/10.1080/15567030903436830
[5] Ramani Narayan. (2006). “Biobased and Biodegradable Polymer
Materials: Rationale, Drivers, and Technology Exemplars.” Degradable
Polymers
and
Materials
[Online].
pg.282-306.
Available:
http://pubs.acs.org/doi/pdf/10.1021/bk-2006-0939.ch018
[6]Thomas Higham. (2002, August 9). “Age Calculation” C14dating
[Online]. Available: http://www.c14dating.com/agecalc.html
[7]University
of
Wisconsin-Milwaukee.
“Liquid
Scintillation”
Environmental Health, Safety and Risk Management Radiation Safety
Program
[Online].
Available:
http://www.bio.huji.ac.il/upload/Beta_Counter_Protocol.pdf
[8] European Food Emulsifiers Manufacturers Association “What is an
Enulsifier”
efema
[Online].
Available:
http://www.emulsifiers.org/ViewDocument.asp?ItemId=11&Title=What+is
+an+emulsifier%3F
[9]Purdue University (2012) “What Is AMS?” Accelerator Mass
Spectrometry
[Online]
Available:
http://www.physics.purdue.edu/primelab/introduction/ams.html#analyzing
Magnet
[10]G. Jackson, Z. Muccio. (14 Nov 2008) “Isotope ratio mass
spectometry”
Analyst, Vol. 134, pg. 213-222 [Online] Available:
http://pubs.rsc.org/en/content/articlehtml/2009/an/b808232d
[11] Srikanth Pilla. (2011). “Handbook of Bioplastics and Biocomposites
Engineering Applications”. Salem, MA: Scrivenger. pp. 128-129
[12] Slawomir Dutkiewicz. (1999). “Synthesis of Poly(L(+) Lactic Acid)
by Polycondensation Method in Solution.” Fibres & Textiles in Easter
Europe. Vol. 11.
[13] (2007, July). “Polyhydroxyalkanotes – The Biodegradable Plastics.”
[Online]. Available: http://www.gate2biotech.com/polyhydroxyalkanoatesthe-biodegradable-plastics/
[14] (2010, November). “Scientists Train Bacteria to Make Bioplastics”
Medical Daily. [Online]. Available:
http://www.medicaldaily.com/news/20101122/4053/scientists-train-
ACKNOWLEDGMENTS SECTION
We would sincerely like to acknowledge our writing
instructor, Keely Bowers, and the Writing Center for the
great feedback on our papers. We would also like to thank
our Co-Chair, Peter Hoffmann for sharing with us what he
learned while doing the paper last year.
6