In recent years, plastics recycling has become a favorite battle cry of environmentalists, one reason being the worldwide love affair with the automobile. By sheer volume alone, the associated waste is overwhelming--more than 2 billion pounds of automotive plastics ended up in landfills or incinerators in 1999 alone. And according to Mark Lieberman, CEO of American Commodities, a large recoverer of post-consumer automotive plastics, a large chunk of that is composed of black plastics, which aren�t that easy to sort for recycling.
The problem, reports Edward Grant, CEO of instrument maker SpectraCode (West Lafayette, IN) and a professor of chemistry at Purdue University (West Lafayette, IN), stems from the inability of a standard spectrometer to quickly detect the component resins of black plastics without overheating or burning the sample. Black plastics, unlike light-colored plastics, are loaded with carbon. When an intense light source, such as a laser, is used to analyze them, this carbon causes the plastics to absorb light to such a degree that the material can heat up and emit light or even ignite. The signal from this luminescence or burning of the plastic, in turn, obscures its spectroscopic signature, making it difficult for sensors to accurately read the plastic's composition.
Raman spectroscopy is one technique that works well on all but black plastics. The main limitation is that it can only sense the composition of the samples at lower laser powers with relatively long (10-s) measurement times. While mid-infrared spectrometers are able to analyze black plastics in some situations, in practice, these spectrometers require similar analysis times and suffer other limitations, including the requirement for flat reflective samples free of surface films.
Grant believes the solution lies in a modified probe that uses a sampling technique SpectraCode calls distributed focusing (a way of rapidly moving the laser focus around without losing any of the backscattered signal). Used in conjunction with the company's RP-1 point-and-shoot, high-resolution Raman imaging spectrograph, this devise reportedly can extract a definitive signature from most black plastics in less than half a second. The firm introduced the distributed focusing technology last November and is accepting orders for delivery the new equipment this quarter.