Fast Identification of Plastic Materials by Near-Infrared Spectroscopy

The recycling or the thermal disposal of plastics is only possible after a rigorous process of separation into classes of compatible materials is conducted. An automatic sorting process leads to recyclates which can be re-used in an economic way. Unknown plastic materials such as basic polymers, fillers and some critical additives, e.g., fire retardants, must be identified. Near-infrared spectroscopy (NIRS) allows the identification of basic polymer, because absorption or reflectance spectra deliver 'finger prints` of polymers and also provide an additional information on some additives. A NIR-spectrometer based on an acousto-optic tunable filter scans the spectral range required for identification, in milliseconds. A transputer system controls the spectrometer, acquires and analyzes the spectra on-line. The integration into a separation process has been done.