The Use of HyperSpectral Imaging for Quality Control in the MDS-based Recycling Process of Polyolefins

The separation of pure polyolefins, polyethylene (PE) and polypropylene (PP), from post-consumer plastic waste is of increasing interest in the last years according to market requirements for their further recycling. In this paper new analytical inspection strategies, based on HyperSpectral Imaging (HSI) in the VIS-NIR and NIR fields (400-1000 and 1000-1700 nm, respectively), have been investigated and set up in order to define quality control logics that could be applied at industrial plant level for polyolefins recycling. Such an approach was developed inside the European FP7 Project W2Plastics “Magnetic Sorting and Ultrasound Sensor Technologies for Production of High Purity Secondary Polyolefins from Waste”. The core of this project is the separation of pure PP and PE based on an innovative process, the Magnetic Density Separation (MDS). Spectra of virgin polyolefins and of plastic particles and contaminants from post-consumer complex wastes (Automotive Shredder Residue and Building & Construction Waste) have been acquired by HSI and by Raman spectroscopy. The classification results obtained applying the principal component analysis (PCA) on HSI data have been compared with those obtained by Raman spectroscopy, in order to validate the innovative sensing methodology. Results shown that it is possible to identify both polyolefins and contaminants based on HSI sensing technique, and that HSI has a great potentiality to be applied for quality control of process feed (presence of contaminants in the plastic waste) and of the two different pure PP and PE flow streams obtained from the MDS-based recycling process.