Although many Americans dutifully deposit their plastic trash into the appropriate bins each week, many of those materials, including flexible films, multilayer materials and a lot of colored plastics, are not recyclable using conventional mechanical recycling methods. In the end, only about 9 percent of plastic in the United States is ever reused, often in low-value products. With a new technique, however, University of Wisconsin–Madison chemical engineers are turning low-value waste plastic into high-value products.
The new method, described in the Aug. 11 issue of the journal Science, could increase the economic incentives for plastic recycling and open a door to recycling new types of plastic. The researchers estimate their methods could also reduce greenhouse gas emissions from the conventional production of these industrial chemicals by roughly 60 percent.
The new technique relies on a couple of existing chemical processing techniques. The first is pyrolysis, in which plastics are heated to high temperatures in an oxygen-free environment. The result is pyrolysis oil, a liquid mix of various compounds. Pyrolysis oil contains large amounts of olefins — a class of simple hydrocarbons that are a central building block of today’s chemicals and polymers, including various types of polyesters, surfactants, alcohols and carboxylic acids.