Thursday, May 13, 2010
Biodegradable OR Compostable Plastic?
What's the difference? Plenty! I didn't think there was any big difference, but there actually is.
Products labeled 'biodegradable' will break down over time by the action of microorganisms, but they may create methane (a greenhouse gas) and they may contain toxins.
Products labeled 'compostable' must be able to break down into carbon dioxide, water and biomass at the same rate as paper. Furthermore, they should not produce any toxic materials and should be able to support plant life. Compostable products are usually made from plant materials. Because the term biodegradable has no real enforced legal definition, compostability is more desirable.
I just bought a tube of water-clear 16 oz. food containers made of PLA for freezing seedless raspberry purée so I can sell it, and the containers are compostable, not just biodegradable. Polylactic acid (PLA) is a material made from lactic acid. The lactic acid is made from dextrose by fermentation; the dextrose is made from corn starch, and corn starch is made by corn plants from carbon dioxide and water.
PLA's are used to manufacture single-serve cold containers (although some companies make hot beverage containers), like drink cups, serving 'plates', and food containers. However, they are not widely used because the cost can be 15% higher than the cheap plastics we see along the roadsides. I have no idea what beverage containers cost in fast food bulk buying, but as a consumer I can buy 12 oz. compostable cold drink cups for less than a penny each. A 15% increase in container cost would affect corporate profit margins, but just think how it would benefit our planet!
Decomposing PLA's requires a compost pile containing microbes, moisture, air and heat. They will break down in as little as 45 days, although usually a bit longer in backyard composting because our heaps tend to be smaller and not as hot. They will not break down in long, cold composting, nor landfills. It is recommended that compost piles contain no more than 10% PLA's for the most effective composting.
I'm glad to say there is finally a corn by-product I can feel good about.