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Re: [greenyes] Re: Underlying assumptions re: plastic from corn vs. fossil fuel

Here is a link to an update about ASTM work in this area. They look at final product:


At 03:00 PM 11/30/2004, SPENDELOW Peter H wrote:
Jenny did a great job explaining the complexity of comparing bio-based plastics vs plastics from fossil fuels. Thank you Jenny.

One small note concerns the environmental effects of composting bio-based plastics. When we think of composting, we usually think of producing a useful product - compost. That is because when we compost many natural organic materials, we get a solid residue called "compost" which consists of complex organic compounds such as lignins which have partially decomposed, plus also other organic and inorganic substances that can serve as plant nutrients. I don't know if this is the case for the bio-based plastics though. Certainly it is not the case for starch-based plastics. When these compost, they break down quickly into carbon dioxide and water, with nothing left to be called compost. Poly lactic acid (PLA) is slower to compost, so there may be an intermediate solid material left for a while, but it wouldn't surprise me if it too disappears pretty completely and does not add any useful organic component to the compost. If anyone has real data on the compost products produced by composting the bio-based plastics, please post that information (or list an appropriate link) on this listserv.

The other thing to note is that although being biodegradable is certainly good for littered items, it is not good for items that end up in landfills. If the bio-based plastics degrade in landfills, they will form methane and also probably organic acids that can leach heavy metals out of other components of the garbage.

Peter Spendelow
Oregon Department of Environmental Quality

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