Abstract
The identification of black polymers which contain about 0.5 to 3 mass percent soot or black master batch is still an essential problem in recycling sorting processes. Near infrared spectroscopy (NIRS) of non-black polymers offers a reliable and fast identification, and is therefore suitable for industrial application. NIRS is consequently widely used in polymer sorting plants. However, this method cannot be used for black polymers because small amounts of carbon black or soot absorb all light in the NIR spectral region. Spectroscopy in the mid infrared spectral region (MIR) offers a possibility to identify black polymers. MIR spectral measurements carried out with Fourier-transform infrared spectrometers (FTIR) are not fast enough to meet economic requirements in sorting plants. By contrast, spectrometer systems based on the photon up-conversion technique are fast and sensitive enough and can be applied to sort black polymer parts. Such a system is able to measure several thousand spectra per second hence is suitable for industrial applications. The results of spectral measurements of black polymers are presented.
Highlights
Black polymers are widely used in consumer products such as electronic household goods, automobile components or IT goods
The samples were not electrically conductive. This distinction is important because black plastic samples which are electrically conductive absorb the entire radiation in the mid infrared spectral region (MIR) spectral range and could not be characterized
To have a comparison and to evaluate the quality of the measured spectra of the the LITRAN system, the plastic samples were measured with a commercial Fourier-transform infrared spectrometers (FTIR) spectrometer system, the plastic samples were measured with a commercial FTIR spectrometer (Fraunhofer Institut für Physikalische Messtechnik IPM)
Summary
Black polymers are widely used in consumer products such as electronic household goods, automobile components or IT goods. The recycling and reuse of these materials is of substantial value and reliable methods for the identification of black polymers are still under development. For industrial applications identification techniques have to be economical, i.e., fast enough, reliable with respect to long term stability, safe and easy to operate. Methods fulfilling these requirements are suitable for large scale recycling applications. For non-black plastic materials, e.g., household goods, NIRS is the predominant spectroscopic technology. Because of the soot contained in black plastics, NIRS cannot be used, as all light is absorbed, rendering material recognition and classification impossible. MIR spectroscopy is an option to measure and characterize black plastics [1]
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