Microwaves help turn sugar into green plastic.

Epane, G, J-C Laguerre, A Wadouachi and D Marek. 2010. Microwave-assisted conversion of D-glucose into lactic acid under solvent-free conditions. Green Chemistry http://www.dx.doi.org/10.1039/b922286c.

Researchers find that microwaves can speed up a chemical process to convert the simple sugar glucose to a bio-based plastic called polylactic acid (PLA), made with renewable feedstocks. The method uses less harmful components and produces fewer byproducts – both pluses when manufacturing biodegradable plastics.

These findings bring a chemical route to making a key component of PLA – rather than a biological one using microbes – a step closer to reality. A workable process will improve the prospects for continued growth in production of environmentally friendly plastics.

Among renewable, biodegradable plastics, polylactic acid (PLA) is one of the most commercially successful, produced on the scale of hundreds of millions of pounds in the United States alone.

The plastic is made up of repeating units of lactic acid, which is usually obtained from corn or other agricultural sources by fermentation. In this process, the microorganisms must be specially bred to break down the plant material into lactic acid instead of other less valuable chemicals. It’s not an easy task, and fermentation can be very slow, creating a bottleneck in the production of PLA. For this reason researchers are looking into ways to produce lactic acid by a chemical rather than biological route.

The easiest chemical approach starts with glucose, one of the components of table sugar. When glucose is treated with caustic and a metal catalyst, lactic acid is produced—along with a variety of other side products. In the past, this strategy was inefficient: the best yield of lactic acid was just 57 percent, the amount of caustic used was 20 times higher than the amount of glucose, and it consumed valuable metal.

In this study, the yield was increased to 75 percent, and the amount of caustic was 13 times lower than prior attempts. The trick was to use microwave energy, similar to that of an ordinary microwave oven. The microwaves sped up the rate and changed the course of the reaction, cutting down on formation of byproducts. Instead of a precious metal, ordinary alumina was used. Alumina is found in everyday products like ceramics, coatings and toothpaste.