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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