New Vegetable-Based Plastics: What They Are and Are Not

By Elizabeth Ferry, Co-op Food Stores, Hanover and Lebanon NH

Plastics are everywhere in our lives. They are in the clothes we wear, the buses we ride or the cars we drive, and they surround many of the foods we eat. Petroleum plastics are not biodegradable; they may break down into ever-smaller pieces, but they are not absorbed back into the environment. For decades, environmentalists have tried to warn the public about mountains of plastic waste that are creating a mountain of solid waste that someday will become too big to ignore.

So when I saw an advertisement for corn-based plastic containers, I was excited. The words "corn-based," though only half of the name, jumped to the forefront. I envisioned a product that was non-toxic, biodegradable, and made from a renewable resource. It seemed like an answer to consumer requests for the most environmentally sensitive packaging option available.

My reaction was just what the product promoters - the makers of petroleum-based plastic - would have hoped for, a green consumer assuming that cornplastics have a positive effect on the environment. But when I gathered more information, I found that some of the industry's selling points for these alternative plastics were misleading to consumers. Let's take a closer look.

How Plastics Are Made

All plastics are created in a laboratory. One way of defining them is by their molecular structure. Plastics are manufactured in a process known as polymerization.

Polymerization is a chemical reaction in which two or more molecules combine to form larger molecules. These larger molecules are characterized by repeating structural units.

The vast majority of plastics are der ived from petroleum. However, the long polymeric structures that define plastics can be made from other substances as well. Recently, scientists have experimented with plant-based sources such as corn and potatoes. Successful developments include corn-based plastic packaging and potato-based disposable plates, which look more like thick paper than like plastic.

The Product and What It Can Do

Corn-based plastics are the first non-petroleum plastic to reach the broader market. For example, they were used at the 2002 Olympic Games in Salt Lake City, Utah. Wild Oats, a natural super market, reportedly began national use of "corn-tainers" - deli containers made from corn - in January, 2005. The new containers can be used for cold-beverage cups or to hold deli items such as potato salad.

Add Heat and They Degrade

However, corn-based plastics are heat sensitive. They melt if filled with hot food or placed in a microwave - qualities that limit their usefulness at this stage of development.

One might expect that being made from plant-based materials, corn plastics would be biodegradable. While supporters promote them as biodegradable, the claim is somewhat misleading. Cornbased plastics will not degrade in an ordinary compost bin or municipal land fill. The polymerization process changes the corn molecules so that unlike the corn from which they are derived, they do not readily (degrade). Rather, they must be transported to special incineration sites and heated in order for decomposition to take place-often consuming greater amounts of petroleum products than were saved by using corn as the primary material.

How Green is My Corn Plastic?

Plastics developed from corn have some "green" qualities: it is made from a renewable resource. It does not emit toxic fumes when it burns. Further, it can biodegrade, albeit with the addition of heat.

However, it is misleading of advertisers to promote this product as reducing America's reliance on petroleum. Our nation's dependence on oil is related to our use of gasoline for transportation and heating oil to warm our homes. Petroleum-based plastics are not the cause of consumption, but rather the by-product of it. It is the development of alternative energy sources, not corn-based plastics, which will reduce our petroleum consumption.

Consumers who are concerned about the development of genetically modified food crops may have a further critique of corn-plastic: companies such as Cargill and Dow are researching ways to genetically engineer corn specifically for this process.

Are plant-based plastics a green product after all? It is an informed consumer who weighs the different factors and draws his or her own conclusion.

Reprinted with permission.