We’ve all seem them by now. Those neat plastic-ware items like Corn Cups that say biodegradable on the bottom. Uber chic at any outdoor event I assure you. But before becoming comfortable plopping them in the ‘ol worm bin I had to do my due diligence of a compost professional. My report to you:

May it be known to all that composting of these biodegradable cups (and other plastic-ware) is indeed safe for your home composting setup, and depending on the item and method will take anywhere from 3-12 months. Earthworms will most likely eat through them as well but they will have to be broken down well before they do. This of course will happen fastest when chopped and shredded. If that’s all you need to know take it and run, if you want to impress your picnic companions then read on. Just be glad you didn’t have to read through sentences like “The work shows that high molar mass poly(lactic acids) can be ingested by earthworms provided they are disintegrated first. However, they cannot be bioassimilated before hydrolytic degradation generates oligomers.” I just hope they’re talking about the polylactic acids being disintegrated and not my earthworm friends.

I think it’s good to start with what these biodegradable cups actually are. And yes, they are often corn-starch based (typically NatureWorks PLA, PLA=polylactic acid), but perhaps just as often they are sugar cane based (bagasse). There are varying needs for these plastics thus multiple types of “bioplastics.” Clear plastics, are typically PLA, while heavier plastics and styrofoam is replaced by a hardier fiber based material, bagasse or heat molded sugar cane fibers, are used to create bowls, plates, heavier cups, take-out containers, et cetera. Of course these are not rules and much overlapping happens.

There are actually a lot of materials that can be made into biodegradable cups/materials. That idea is actually kind of scary considering they are being are potentially being ingested by us. Luckily for us there is biodegradable products standard through the Biodegradable Products Institute which is carefully making sure that these products are worthy of us eating and drinking from before throwing them into our compost. Most PLA glasses you’ll find in the US will be from NatureWorks, LLC which is accepted on their site.

The bottom-line here is that there are many improvements coming into this industry this day and age. Mostly in the form of Biodegradable Polyesters in which PLA is a part of.

As can be seen from this diagram PLA isn’t necessarily the best of the biodegradable polyesters. A natural plastic from the PHA branch would actually compost quicker. PHBV is actually the front runner from that branch of the polyesters bioplastics. Read about EcoGenTM’s PHBV plastics. One of the main reasons for PLA’s front running is its cost effectiveness and consistency. The one drawback is the composting conditions needed for it to break down completely.

For more detailed information on Bioplastics please read about them on BioDeg.net.

Posted on Sunday, July 27th, 2008 at 4:36 pm under Composting, Questions. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.