I know this is quite a bit late, but I’m just gettin’ here-
First off, everything is pretty much bio-degradable, given enough time (sometimes centuries). Also current landfill practices in the US are to take all waste and basically surround it with compacted clay and an HDPE liner so nothing harmful can leach into the soil and spoil the ground water.
http://www.cpia.ca/files/files/files_Biodegradation_Landfill_Crunch.pdf
This also means that even easily biodegradable materials will not break down at all. There are instances where newspapers are still readable after 40+ years of being in a landfill, and carrots still bright orange in the center.
So making a product biodegradable doesn’t mean that it is necessarily better for the environment if it is still going to end up in a landfill. You really have to look at the complete lifcycle of your product, from manufacture, transportation, and especially the end of life part, to determine the “greenest” methods. How much fuel is used up on a daily basis just by garbage/recycling trucks? Also as you mentioned, what is the chemical make-up of the material as it breaks down? Sometimes this may be more harmful than the original material. All things to consider, although landfill practices may be changing. http://www.environment-agency.gov.uk/business/444217/444663/landfill/986852/987368/?version=1&lang=_e
I really think the McDonough and Braungarts “Cradle to Cradle” philosophy has much potential, in that they propose products that are designed to be re-used as opposed to re-cycled or landfilled. Building on this is the way to go.
Here is a site that has some great links at the bottom to help you out-
http://www.personal.psu.edu/users/c/n/cnh117/scienceresearch.html
.G.