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InGaAs technology passes uPVC challenge

06/14/2012 Bühler's SORTEX InGaAs technology is in a class of its own when removing difficult-to-detect white rubber, silicon and nylon from white PVC. Recycling uPVC windows isn’t an easy task. That’s because white rubber must be detected and removed from the recycled white uPVC. “To complicate things further, white silicon and white nylon can also be present in post-consumer window frames,” explains Faisal Baig, Product Manager. “Same-colour sorting provides a stiff test. White rubber, white silicon and white nylon must be removed to create pure, clean and consistent recycled PVC.”

Many companies combine technologies, but that’s not the best solution says Baig. “Not only is it more expensive and more costly to run, it doesn’t offer high sorting performance or great accuracy. One of our optical sorters fitted with InGaAs technology offers a far superior solution. You’ll get better sorting efficiency; better accuracy and with lower costs. Recent trials we’ve carried out for European uPVC recyclers have proved very successful.”

But how is InGaAs technology able to provide such exceptional accuracy? “The SWIR [short-wave infra-red] spectrum of polymer is so unique that it’s like a molecular fingerprint,” Baig explains. “By interpreting the infrared reflected spectrum, our InGaAs technology can define the appropriate separation required for those specific defects.”

Conventional sorters with silicon sensors can only detect wavelengths in the visible and NIR [Near infra-red] spectrums, whereas InGaAs technology can detect wavelengths in the SWIR region. Crucially, white silicon, white rubber and nylon reflect radiation differently from uPVC in the SWIR region, so it can be identified and removed easily with InGaAs technology.

“Black rubber seal fragments, which can also be present, can easily be removed using visible cameras. Using a combination of visible, PROfile and InGaAs technologies, our sorters can detect every defect in recycled uPVC regrind, shred and pellets – regardless of colour,” he concludes.

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