Purdue Research Park instruments maker SpectraCode Inc has developed a new method to analyse black plastics for recycling purposes.
According to Edward Grant, chief executive officer of SpectraCode and Purdue University professor of chemistry, being able to instantaneously identify and separate post-consumer black plastics by resin type has presented a significant barrier to their wide-scale recycling.
The problem, according to Grant, 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-coloured plastics, are loaded with carbon. When an intense light source, such as a laser, is used to analyse them, the carbon causes black 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 obscures its spectroscopic signature, making it difficult for sensors to read the plastic’s composition accurately.
The RP-1, SpectraCode’s existing point-and-shoot, high-resolution imaging spectrograph, analyses samples with a monochromatic laser and records their vibrational signatures in the Raman spectrum of the back-scattered light. Raman spectroscopy is able to analyse dark and intensely pigmented plastic materials, but with black plastics, it can only sense the composition of the samples at lower laser powers with relatively long, 10 second, measurement times.
Mid-infrared spectrometers, which use absorption from a broadband infrared source, are able to analyse black plastics in some situations. However, these spectrometers require similar analysis times and suffer other limitations. This inability to instantly identify black plastics led Grant’s team to create the new instrument.
SpectraCode’s new technology is said to enable the instant point-and-shoot identification of black plastics, extracting a definitive signature from most black plastics in half a second or less. This speed is achieved through a modified probe that uses a sampling technique called distributed focusing.
The American Plastics Council reports the number of plastics recycling businesses has tripled during the past 10 years, with more than 1,700 businesses handling and reclaiming plastics.
The largest recycler of post-consumer automotive plastics in North America, American Commodities Inc., has been looking for new methods to recycle what currently ends up in landfills or incinerators — more than 2 billion pounds of automotive plastics in 1999.
‘A large fraction of this waste stream is composed of black plastics,’ said Mark Lieberman, chief executive officer of American Commodities Inc. ‘Automotive black plastics — from bumpers to instrument panels to fender liners — have several strikes against them when it comes to recycling. Mid-infrared spectrometers haven’t been successful at analysing them because of their unusual shapes and surface textures.’