Laser eye quickly I.D.'s plastics in waste.
AN OLD 'NEW' TECHNOLOGY
RP-1 uses Raman inelastic light scattering, which is an identification technology first developed in the 1930s and enhanced in the 1960s with the use of lasers. Before now, it was used almost exclusively by research scientists, says Grant. He says the RP-1 system is made simple for non-expert users by two main technology breakthroughs. One is the application of the charge-coupled device (CCD) detector (also used in electronic cameras). It can "see" the full spectrum of scattered visible light all at once, yet is sensitive enough to register one of every two light photons. The second advance is holographic optical elements that can distinguish which photons have interacted with a plastic material and which ones have not.
The user touches the RP-I's gun to the sample and fires the laser with a pushbutton trigger. The laser light penetrates 100 microns into the part. The spot size need be only 0.5 mm. The laser light causes molecules of plastic to vibrate. Certain photons within the spectrum of light emitted by the laser change frequency when they encounter the resin molecules, while others do not. Both types of photons reflect off the plastic and produce a distinctive "vibratory signature" that is unique for each polymer, says Grant. The holographic technology in the gun's detector captures the reflected light, keeping only the photons that have changed frequency. This light signature is transferred through a fiber-optic cable to a computer console with a "library" of collected material signatures that is searched to find a match. The user can expand the library.
The RP-1 reportedly overcomes one of the biggest obstacles in durable-goods recycling - identification of darkly pigmented materials. The unit can also identify the material even if the surface of the part is textured, dirty, or coated. The RP-1 successfully distinguishes ABS from PS and from PPO, and it can "see" PC beneath an acrylic coating, Grant says. Such distinctions are reportedly difficult or impossible with current near-infrared (NIR) and mid:infrared (FTIR) identification technologies. Overall, the RP-1 has better resolution and speed than available IR technology, giving accurate readings in under 1 sec.
NEXT STEP IN I.D.
The unit still has some obstacles to overcome, Grant says. It is somewhat sensitive to the presence of carbon black, which absorbs light so less is reflected back to the detector. The laser can also excite certain types of molecules in a material to fluoresce, which can make identification more difficult.
Grant says the next step is accurate detection in the presence of high-carbon or heavily pigmented structures. The RP-1 may eventually be able to identify materials in a moving stream automatically.
The RP-1 was developed under real-world conditions at the automotive recycling facilities of Butler-MacDonald in Indianapolis. The components were supplied by Ford Motor Co. SpectraCode has sold units to both Butler-MacDonald and to Ford. The unit costs $75,000 for the hand-held probe, mobile console, and software that controls and collects the data and performs the identification.
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|Comment:||Laser eye quickly I.D.'s plastics in waste.|
|Date:||Dec 1, 1997|
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