Fast and automatic thermographic material-identification for the recycling process

Within the framework of the future closed loop recycling process the automatic and economical sorting of plastics is a decisive element. The at the present time available identification and sorting systems are not yet suitable for the sorting of technical plastics since essential demands, as the realization of high recognition reliability and identification rates considering the variety of technical plastics, can not be guaranteed. Therefore the Laser Zentrum Hannover e.V. (LZH) in cooperation with the Horotron GmbH and the Preussag Noell GmbH has carried out investigations on a rapid thermographic and laser-supported material-identification-system for automatic material-sorting-systems. The automatic identification of different engineering plastics coming from electronic or automotive waste is possible. Identification rates up to 10 parts per second are allowed by the effort from fast infrared line scanners. The procedure is based on the following principle: Within a few milliseconds a spot on the relevant sample is heated by a CO2 laser. The samples different and specific chemical and physical material properties cause different temperature distributions on their surfaces that are measured by a fast IR-linescan system. This "thermal impulse response" (TIR) has to be analyzed by means of a computer system. Investigations have shown that it is possible to analyze more than 18 different sorts of plastics at a frequency of 10 Hz. Crucial for the development of such a system is the rapid processing of imaging data, the minimization of interferences caused by oscillating sample geometries, and a wide range of possible additives in plastics in question One possible application area is sorting of plastics coming from car- and electronic waste recycling.