Originally Posted by travlineasy
There is a biodegradable plastic available, but it's tensile strength is garbage. It's made with corn starch, and takes about 6 years to fall apart. And, it needs direct sunlight in order to deteriorate into dust. When buried in a landfill, it lasts forever.
For our 2012 party I bought a bunch of corn starch keg cups for the beer. They're as strong as any petroleum plastic, at least when you're talking about holding beer for one night, and they do seem to be breaking down without sunlight. I put them in a compost pile and they are definitely breaking down. Slowly. Very slowly. I'm 14 months out in this experiment and just turned the pile. The thinnest edge parts are already gone, the thick parts have clouded over and are fragile. I think another year or two and they'll be gone. Anyway, it all goes into my garden.
For this year's party I went with paper cups that are coated with a thin layer of corn plastic. They worked great as beer cups, and are already breaking down into compost. I think they'll be decomposed and in the garden next spring.