Here is a link to an update about ASTM work in this area. They look at
final product:
http://www.astm.org/cgi-bin/SoftCart.exe/SNEWS/APRIL_2001/mojo_apr01.html?L+mystore+phnr8679
H.
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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