Corn-based bioplastic packaging is made with polyactic acid (Pla), which closely resembles typical PET (polyethylene terephthalate) plastic, is widely used by large food groups and grocery chains, including McDonald's and Wal-Mart, and bottlers. Though proponents claim Pla helps extend products' shelf life and cut emissions production during the manufacturing process, the study found that it barely broke down and could only be composted in anaerobic digesters, all of which do not take packaging. Pla bags that end up on landfill sites release methane, a very potent GHG, when they degrade.
Moreover, its inclusion in recycling operations can contaminate the other materials and make recycled (conventional) plastics unsaleable. To handle bioplastic packaging, recycling companies would need to invest in very expensive, cutting-edge machinery that could extract the Pla from waste.
Then there is the problem with so-called "oxy-degradable" plastic bags, which supermarkets are promoting as the "sustainable" alternative to PET bags. Although it's true that these bags, which contain an additive that facilitates the breakdown of plastic, are, in fact, biodegradable (in principle), the fact that they eventually end up in an anaerobic landfill site means they won't degrade effectively.
As Chris Goodall, an environmental author and analyst points out: "People think that biodegradable is good and non-biodegradable is bad. That's all they see." In practice, that distinction is not always so evident. As with biofuels, we need to find better alternatives to feed stocks and ensure that the bags degrade properly -- both not easy objectives. Perhaps more bags made out of cow poop?
Via ::The Guardian: 'Sustainable' bio-plastic can damage the environment (news website)