Author: Dan Maloney / Source: Hackaday
If you’ve ever taken a coast-to-coast car trip across the United States, the one thing that’s sure to impress you is the mind-bogglingly immense amount of corn that we grow here. If you take the northern route — I’ve done it seven times, so I know it by heart — you’ll see almost nothing but corn from Ohio to Montana.
The size of the fields is simply staggering, and you’re left wondering, “Do we really eat all this corn?”The simple answer is no, we don’t. We grow way more corn than we can eat or, once turned into alcohol, drink. We do feed a lot to animals, many of which subsequently end up as burgers or pork chops. But even after all that, and after accounting for exports, we still have a heck of a lot of corn to put to work. There are lots of industrial uses for this surplus corn, though, and chances are pretty good you’ve got an ear or two worth coiled up next to your 3D-printer, in the form of polylactic acid, or PLA.
Forget the Fossils
Most of us give little thought to where plastics come from, and those that do are more likely than not to assume that plastics come from petroleum. For most of the history of the polymer industry, that was a safe bet, but with the relatively recent introduction of engineered bioplastics, the industry had a new feedstock: recently deceased plants rather than fossilized ones. (This doesn’t include biopolymers taken from nature, like cellulose and latex, that are used more or less directly; Mother Nature is a surprisingly good polymer chemist.)
Whether a biopolymer is naturally occurring or synthesized industrially, the basic principles are the same. All polymers are made up of small, repeating units, called monomers, that are linked together chemically into long chains. A simple example of a non-biopolymer is polyethylene, where the monomers are the two-carbon alkene ethylene. The properties of the monomers, their numbers, and the configuration of the chains largely determine the characteristics of the resulting plastic, and the huge number of combinations of these factors leads to the incredible diversity of polymers in use today.
While polylactic acid — which is more correctly styled “poly(lactic acid)” since the monomer is lactic acid — has come into widespread only relatively recently, its history stretches back to the 1930s. Unsurprisingly, it was yet another product the E.I. du Pont de Nemours Company’s sprawling research labs in Wilmington, Delaware. That it also was the brainchild of Wallace Carothers, the troubled genius responsible for Nylon and Neoprene, is perhaps a bit surprising, since those synthetic polymers were made from petrochemicals such as coal tar and acetylene….
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