New Food Container Materials II

Bioplastics: The theory behind bioplastics is simple: if we could make plastics from kinder chemicals to start with, they'd break down more quickly and easily when we got rid of them.

The most familiar bioplastics are made from natural materials such as corn starch. Some bioplastics look virtually indistinguishable from traditional petrochemical plastics. Polylactide acid (PLA) looks and behaves like polyethylene and polypropylene and is now widely used for food containers.

Unlike traditional plastics and biodegradable plastics, bioplastics generally do not produce a net increase in carbon dioxide gas when they break down. PLA, for example, produces almost 70 percent less greenhouse gases when it degrades in landfills.

Another good thing about bioplastics is that they're compostable. They decay into natural materials that blend harmlessly with soil. Some bioplastics can break down in a matter of weeks. The cornstarch molecules they contain slowly absorb water and swell up, causing them to break apart into small fragments that bacteria can digest more readily.

Biodegradable plastics: If you're in the habit of reading what supermarkets print on their plastic bags, you may have noticed a lot of environmentally friendly statements appearing over the last few years. Some stores now use what are described as photodegradable, oxydegradable, or just biodegradable bags (in practice, whatever they're called, it often means the same thing).

As the name suggests, these biodegradable plastics contain additives that cause them to decay more rapidly in the presence of light and oxygen (moisture and heat help, too). Unlike bioplastics, biodegradable plastics are made of normal (petrochemical) plastics and don't always break down into harmless substances, sometimes, they leave behind a toxic residue and that makes them generally (but not always) unsuitable for composting.

Recycled plastics: One neat solution to the problem of plastic disposal is to recycle old plastic materials into new ones. A product called eco-plastic is sold as a replacement for wood for use in outdoor garden furniture and fence posts. Made from high-molecular polyethylene, the manufacturers boast that it's long-lasting, attractive, relatively cheap, and nice to look at.

But there are two problems with recycled food plastics. First, plastic that's recycled is generally not used to make the same items the next time around. For example, old recycled plastic bottles don't go to make new plastic bottles, but lower-grade items such as plastic benches and fence posts. Second, you can't automatically assume recycled plastics are better for the environment unless you know they've been made with a net saving of energy and water, a net reduction in greenhouse gas emissions, or some other overall benefit to the environment.