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08/02/2006
Corny Material
Kermit was right again. It isn’t easy being green. Even well
meaning efforts to behave in an environmentally friendly fashion
have their limitations. Corn plays a big role in two such efforts.
Most of us are filling our tanks with gasoline to which ethanol
derived from corn is added. Last fall, Wal-Mart announced that
it was making a major commitment to using a biodegradable
plastic, polylactic acid (PLA), to package a sizeable number of
its products. A company called Nature Works runs the world’s
largest lactic acid plant in Blair, Nebraska and the raw material is
corn. In an article, “Corn Plastic to the Rescue?” in the August
Smithsonian magazine, Elizabeth Royte takes a close look at the
good and the bad news about PLA.
We’ve talked in past columns (8/15/2002 and 8/22/2002) about
the major role that corn plays in our lives. Last week I skipped
buying an unfamiliar brand of applesauce that contained high
fructose corn syrup (HFCS), only to find that the brand I’ve
preferred for years also contains HFCS. In the first column, I
noted the high percentage of calories we consume as HFCS in a
multitude of products and the possible role HFCS plays in the
fattening of America.
Don’t get me wrong. I enjoy a good ear of fresh corn as much as
anyone. So let’s see how you get from corn to the plastic PLA.
Royte describes driving to visit the Nature Works plant in
Nebraska and encountering the damp, sweet odor of steaming
corn well before coming upon the “enormous, steam-belching”
plant of tanks and pipes springing up out of the cornfields. In the
plant, kernels of corn are milled and the starch is separated from
dextrose, which is fermented in huge tanks to give lactic acid.
Lactic acid (CH3-CHOH-COOH for you chemistry students) is a
compound produced in the body that plays a role in muscle
fatigue. The compound lactose found in milk, reacts with
bacteria to form lactic acid, which curdles the milk along the way
to becoming cheese.
But I digress. In the Nebraska plant, the lactic acid is converted
into a compound called lactide, which in turn is converted into
pellets of a polymer, our polylactic acid or PLA. These pellets
are shipped to a nearby company that melts the pellets and
presses and stretches the melted pellets into thin sheets. The
sheets are stamped into molds to form the different shaped
packages. So, what’s the good news about PLA? According to
Royte, the manufacture of conventional plastics in the U.S.
devours an estimated 200,000 barrels of oil per day. On the
other hand, PLA derives from the corn, a renewable resource, an
obvious plus for the environment. In addition, the article states
that producing PLA consumes about 65% less energy and
generates about 68% less greenhouse gases than does the
production of common plastics. PLA also doesn’t contain toxins.
PLA is touted as being biodegradable, implying that you can toss
your PLA packaging into your compost pile and it will turn into
water and carbon dioxide. (If you’re a city dweller, it’s unlikely
that you have a compost pile. I once was into organic gardening
and had a compost pile in our backyard but it was always a bone
of contention with my wife.) In principle, that carbon dioxide
released by the composting PLA will be retrieved from the
atmosphere to grow more corn to make more PLA. That’s one
advantage of a renewable resource such as corn. Everything is
fine with regard to the CO2 balance and global warming. That’s
the good news. The bad news: it seems that you can’t just toss
the waste PLA into your compost pile and expect it to go away.
To compost PLA, it takes a special kind of compost pile in which
plant scraps and microbes get together to raise the temperature
up to 140 degrees Fahrenheit. To get PLA to convert to CO2 and
H2O, the compost pile has to maintain that temperature for 10
days, according to Royte. She only knows of 113 such
composting facilities in the U.S. and only a quarter of these take
food scraps collected by various communities. There also seems
to be some controversy about PLA and the likelihood that there
will be enough special facilities to handle its composting. Some
say that when the amount of PLA reaches a critical value it will
be like the field of dreams in the Kevin Costner movie – make
enough PLA and the compost facilities will come.
I searched the Web and found a good bit of work in progress on
composting PLA and on combining PLA with other materials.
There is also some work going on in the area of converting wheat
to plastic. Some question the “morality” of converting a
foodstuff such as corn to packaging. Others question whether we
really need so much plastic packaging. I remember the days
when milk came in bottles and we left our empty bottles out for
the milkman to take back to the dairy for cleaning and reuse.
Offhand, I should think that this would be a greener approach
than the plastic or cardboard packaging now in use. However,
the milkman seems to be an endangered species (we still have
one) and it would be more inconvenient to have to lug empty
bottles back to the supermarket.
Yesterday, we drove into New York for a medical procedure.
The temperature either hit or was flirting with 100 degrees
Fahrenheit and it’s higher today. Which brings up another bit of
bad news about PLA. The melting point is only 114 degrees
Fahrenheit. If your PLA package is in your car in the sun, the
temperature can easily be 120 degrees or higher and your
package may have lost any resemblance to its original shape!
However, Newman’s Own Organics has been using PLA
containers for its salad mixes for a number of years, as has Wild
Oats for some of its products.
Realistically, although PLA represents a laudable step forward
towards an environmentally benign plastic, chances are that a
large amount of it will not end up in the special composters but
will end up in landfill. In a landfill, the PLA will probably last
for about the same length of time as other packaging plastics,
perhaps for centuries.
I had planned to write a bit about that ethanol from corn but I just
came back from another medically oriented trip in this miserable
heat and I’m pooped. In addition, the heat has given me a case
of writer’s block. Keep cool, wherever you are.
Allen F. Bortrum
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