Compostable Corn-Plastic? Yes and No

Posted by Sustainable OKC | Posted in Compost, Public Works, Science, Tricia Dameron, Waste Management | Posted on 23-01-2009


by Tricia Dameron

New "bioplastics" are labeled "compostable" but require industrial composting processes.
Human ingenuity has discovered yet another use for corn: bioplastic,
specifically in the form of 
disposable flatware. Have you seen these
products? You might not even know the difference, except that they melt
a lot easier. They look just like their petroleum-based counterparts.
What's the attraction? Well, for one, they are not made from petroleum.
That's a plus. But, they are made from a foodstuff, which is a growing
concern in this age of corn ethanol. Another advantage of polylactic
acid (PLA), the technical name for the resin, is that it's compostable. Well, at least that's what one
would assume from reading the product label. However, that's not the
complete Five months in the compost pile has caused no change in the "compostable" corn-based plastic cups.
story. It's compostable, yes, but only in a commercial
facility.  According to this Scientific American
article, there are only 113 
industrial-grade composting facilities in
the U.S. I wonder how many of these facilities accept public drop-offs?
Some of these products are labeled with the term "biodegradable." To be
clear, these items are not biodegradable in a landfill; they might
degrade in 100 or 1,000 years. Landfills are designed to entomb our
waste to prevent contamination of the environment; in turn, the
"bio"—the sun, air, fungus—of "biodegrade" is removed from the process.

Products marked code 7 are accepted by Waste Management, but it is unclear whether they are actually recycled.
So, if backyard composting doesn't work, can you put them in your
recycle bin? Apparently, it's not that straightforward. NatureWorks, a
PLA manufacturer owned in-part by Cargill, says PLA has no negative impact on the quality of flake produced from recycling PET and HDPE plastics. Yet, this Smithsonian article states that PLA is considered a contaminant when found in the recycle stream of PET. Some bioplastics may be imprinted with resin code 7. If so, these are accepted by Waste Management in Oklahoma City, but are they actually recycled? No industry representative would go on the record to confirm or deny it.

situations where reusable plates and flatware are not feasible, it
would be nice to have an option like these corn-based plastics—an
option made from renewable resources that biodegrade. However,
at this point it seems our infrastructure does not support the intended
benefits of these products. It would also seem that there needs to be truth in marketing to reflect these limitations.

Comments (6)

Nice post. Thank you! Appreciate the time you took to slice-and-dice the pros and cons, and track down research to help us make better choices. Very useful!

Good to know. I hate greenwashing!

What about the disposable paper products labeled “compostable”? Has anyone had success composting them in a residential pile?

I didn’t realize the corn products couldn’t go in a compost bin. It seems that the more we try to control every aspect of our waste, the more work and confusion we create for ourselves.
Lately, when I’ve been thinking about issues such as this, I continually return to pondering how, of the three R’s, “Reduce” is really the most valuable in our everyday thinking.
Too bad we haven’t figured out a profitable way to market that yet. Or even better, too bad we haven’t figured out, as a society, that being profitable isn’t the most “valuable” part of life.

There are a lot of problems with PLA – If we made all of the plastic disposable items used in the world every year out of PLA, it would take one hundred million tons of corn to make it. That would lead to mass starvation in the third world, as that represents at least 10% of the world’s grain supply. Also, in landfills, PLA exudes methane when it decomposes-and methane is a potent greenhouse gas. It also takes a huge amount of diesel to grow, fertilize, ship, and process this corn. As a practical matter, it is also not recyclable. The alternative? Oxo-biodegradable plastics. See for full information. -Tim Dunn

Most of the commercial compost facilities only accept yard waste. And oxo-biodegration would be of no consequence if material is landfilled but could benefit in the backyard compost scenario.