,
the nearly indestructible plastic used to make most containers and
bottles. Drop the same bottle into a landfill, however, and you might
have second thoughts. Why? Because petroleum-based plastics like PET
don't decompose the same way organic material does. Wood, grass and food
scraps undergo a process known as
in the soil into other useful compounds. But bacteria turn up their
noses at plastic. Load their dinner plates with some plastic bags and
bottles, and the one-celled gluttons will skip the meal entirely.
Based
on this logic, it's safe to argue that plastic will never biodegrade.
Of course, that's not the end of the story. Daniel Burd, a student at
Waterloo Collegiate Institute, recently demonstrated that certain types
of bacteria can break down plastic. His research earned the top prize at
the Canada-wide Science Fair, earning him $10,000 cash and a $20,000
scholarship [source:
Kawawada].
Until
other researchers can replicate Burd's experiment and waste treatment
plants can implement any new processes, the only real way to break down
plastic is through photodegradation. This kind of decomposition requires
sunlight, not bacteria. When
UV rays
strike plastic, they break the bonds holding the long molecular chain
together. Over time, this can turn a big piece of plastic into lots of
little pieces.
Of course, plastic buried in a landfill rarely sees
the light of day. But in the ocean, which is where a lot of discarded
grocery bags, soft drink bottles and six-pack rings end up, plastic is
bathed in as much light as water. In 2009, researchers from Nihon
University in Chiba, Japan, found that plastic in warm ocean water can
degrade in as little as a year. This doesn't sound so bad until you
realize those small bits of plastic are toxic chemicals such as
bisphenol A (BPA) and PS oligomer. These end up in the guts of animals
or wash up on shorelines, where humans are most likely to come into
direct contact with the toxins.
One solution to this environmental disaster is biodegradable plastic. There are two types currently on the market --
plant-based hydro-biodegradable plastic and
petroleum-based oxo-biodegradable plastic. In the former category,
polylactic acid (
PLA),
a plastic made from corn, tops the list as the most talked-about
alternative. PLA decomposes into water and carbon dioxide in 47 to 90
days -- four times faster than a PET-based bag floating in the ocean.
But conditions have to be just right to achieve these kinds of results.
PLA breaks down most efficiently in commercial composting facilities at
high temperatures. When buried in a landfill, a plastic bag made from
corn may remain intact just as long as a plastic bag made from oil or
natural gas.
Keep reading for more links you might like on plastics."
http://science.howstuffworks.com/science-vs-myth/everyday-myths/how-long-does-it-take-for-plastics-to-biodegrade1.htm
What is corn plastic?
"
For years, the corncob pipe was a fashion accessory best left to
hillbillies, Frosty the Snowman and Gen. Douglas MacArthur. While the
look is no less bumpkinish today than it ever was,
corn
is showing up in the production of more everyday items -- and without
resembling a prop from "Hee Haw." What looks like normal oil-based
plastic at first glance is actually
polylactic acid (
PLA)
plastic made from specially processed crops.
That's right:
corn plastic. You can drink
coffee
out of it, put groceries in it, wear it and even hang ten on it on a
corn plastic surfboard. Most important, you can turn corn into plastic
and avoid dependency on
petroleum. Much like corn
ethanol,
corn plastic allows us to make a comparable product out of a renewable
resource, as opposed to oil reserves that will one day run dry. In
addition, since corn can be cultivated throughout the world, market
value doesn't hinge on relationships with oil-rich nations or on peace
in the Middle East. After all, have you ever seen "No blood for corn"
printed on a T-shirt?
The United States uses 20.8 million barrels
of oil per day, 10 percent of which goes solely to the production of
conventional plastic such as
polyethylene terephthalate (
PET) [sources:
CIA World Factbook,
Jewell].
Bioplastics like corn plastic, however, don't require oil and, as a bonus, their manufacture releases fewer toxins and greenhouse gases.
Plus,
while normal plastic has a nasty habit of sticking around for centuries
after disposal, corn plastic boasts the ability to biodegrade in mere
months. Moreover, should you choose to burn it, you don't have to worry
about creating toxic fumes.
In this article, we'll look at how a
corn stalk turns into a plastic garbage can and why some critics aren't
convinced that bioplastics are necessarily a godsend.
Bioplastics: The Pros and Cons
Globally, bioplastics make up nearly 331,000 tons (300,000 metric tons) of the plastics market [source:
European Bioplastics].
That may sound like a lot, but it only accounts for less than 1 percent
of the 200 million tons (181 million metric tons) of synthetic
plastics the world produces each year [source:
Green Council]. Still, the bioplastics market is growing by 20 to 30 percent each year, but not everyone's pleased [source:
Vidal].
What
could be wrong with a renewable resource you grow in a field and
compost when you're done with it? As it turns out, several things. For
one,
corn plastic only
composts in the hot, moist settings of a commercial composting facility. Simply throw a corn plastic product out of your
car or bury it in a backyard-composting heap and the material will stand the test of time just as regular PET plastics will.
If commercial composting isn't available, PLA plastics can wind up following conventional plastics into the
landfill or into plastic
recycling
programs. What's wrong with putting corn plastics in your recycling
bin? To the uninformed eye, one may look very much like the other, but
their chemical composition is very different. In fact, a relatively
small amount of bioplastic can contaminate conventional plastic
recycling, preventing the salvaged plastic from being reused and
stopping recycling companies from profiting from one of their more
lucrative recyclables.
Due to these dangers, companies like
NatureWorks are treading carefully, introducing corn plastic products
slowly and communicating with commercial recyclers to spot contamination
early. Bioplastics manufacturers insist that the threat is overblown
and that recycling remains a better option than composting for PLAs such
as corn plastic, since it makes up such a small percent of the current
plastics market. In addition, since PLA plastics produce the greenhouse
gas
methane when they decompose, composting isn't a
perfect disposal method. On the other hand, if incinerated, bioplastics
don't emit toxic fumes like their oil-based counterparts.
To avoid
the complications of mixed plastics, commercial composters in the
Northwestern United States only accept bioplastics from food service
operations, not households. This approach means that bioplastics could
conceivably be used to great effect at sports games and other events
where foods are purchased and consumed on the premises in bulk.
As
with corn ethanol, corn plastic has also drawn criticism for depending
on the industrial farming of large fields of crops. These fields could
otherwise be used to grow food for an ever-rising global population.
Much of the corn used for bioplastics is a variety called Number 2
Yellow Dent that's used mostly for animal feed. In addition, some of
this corn used has been genetically modified. Nevertheless, even if
genetically modified corn was used to make your plastic water bottle,
NatureWorks insists that you don't have to worry about consuming
modified proteins, as these are destroyed in the transformation from
plant to PLA plastic [source:
Jewell].
Advocates
also stress that the bioplastics industry is in its infancy, with
long-term plans of being able to depend exclusively on agricultural
waste (such as stems and stalks) for production. Such plans are also
mentioned in defense of the higher costs associated with bioplastics
research and production. PET plastics are a mature commodity, with years
of production fine-tuning behind it. Bioplastics advocates argue that,
in time, PLA costs will go down, all while petroleum-based plastics
costs continue to fluctuate due to unstable production regions and
dwindling resources.
Explore the links on the next page to learn even more about plastics, corn, biofuel and recycling.
http://science.howstuffworks.com/environmental/green-science/corn-plastic3.htm
