Automated Separation of Plastic Resins Types by the Second Order Derivative Method Based on NIR Reflectance Spectroscopy

In this paper, an appropriate, accurate and fast method for automated separation of plastic resins from post consumer plastic wastes is presented. The principle of sorting system operation is based on Near Infrared (NIR) reflectance spectroscopy. In this system, the plastic samples are fed on the sorting conveyor. When the samples are crossing from the near of conveyor end, their NIR reflectance spectrum is taken by a rapid spectrometer device. The control unit takes the second derivative of spectrum graph and then recognizes the sample material by analyzing this graph. Finally the target plastic resin is thrown to proper location by compressed air jet. According to current study, it is possible to separate PET, HDPE, PVC, PP and PS resins automatically by LabVIEW software. The accuracy of this method has been demonstrated for different resins. Also the effect of various parameters such as surface pollution, sample thickness and existence of label and cap has been studied on identification system. Experimental results, have confirmed the high accuracy of this new method.