Conventional plastics are made from fossil fuels– oil and gas.
By contrast, the raw material for bioplastics is plants, so bioplastics are made from renewable resources, and they are also potentially biodegradable and non-toxic. The most common source for bioplastics right now is polylactic acid (PLA) from corn. But other plant sources in use include bagasse (sugar cane fiber), soybeans, and potatos. Here is an interesting video about how PLA is made:
(Warning: Inexplicably this video describes corn plastic as edible…please don’t try this at home!)
For the most part bioplastics look and act like conventional plastics (PLA does not hold up well to heat, so can’t be used to contain things like soup), but bioplastics cannot be recycled like some petroleum based plastics. And bioplastics will contaminate traditional plastics if accidentally mixed with them, which makes them problematic for recyclers.
Image: Bec, couresy Flickr (via Scientific American)
Because bioplastics look just like regular plastic, they are hard to sort out, and you’ll get no help by looking for a resin code. At present, bioplastics fall under the #7 plastics resin code, which is a catchall category for many types of plastic, including petro-plastics. Considering that bioplastics like PLA are much more common nowadays, it’s amazing that they don’t as yet have any recycling code or other required features that would help consumers or recyclers distinguish them.
Bioplastics are also a big problem for composters, because while they are theoretically compostable, many of them do not biodegrade on the same timetable as organics like food and yard waste, even in a commercial composting facility. A recent article in the San Anselmo/Fairfax (CA) Patch investigated the real world state of bioplastics management in Marin County. While many citizens had been feeling pleased and proud about adopting bioplastic foodware, the sad fact is that bioplastics have to be screened out of Marin’s composting facilities and landfilled. They simply don’t biodegrade in 30 days in a windrow. Even San Francisco’s commercial composting facility, Jepson Prairie Organics, which has a more intensive process, can’t compost all incoming bioplastics.
And bioplastics are a big problem for those concerned with environmental health, too. Why? Because manufacturers are secretive about the composition of their products. So long as bioplastic recipes remain proprietary, there will be concerns about what chemical additives may be going into the product, and thence to the compost. The whole point of creating compost, after all, is to make a useful soil amendment that is safe, and actually benefits, rather than impedes, plant growth.
Two other concerns about bioplastics from corn arise. First, should we be using corn or any other food crop for bioplastics when corn can help feed a starving world? And second, would growing corn as a feedstock for plastics drive the production of even more herbicide- reliant GMO/monoculture corn?
Adding to the perplexity are products billed as bioplastics that are plant and petro hybrids or ethanol-based plastics, like Coke’s PlantBottle. Though they sound promising, these products fall far short of being good for the environment. More on the PlantBottle in my next post.