The Utilization of Hyperspectral Imaging for Impurities Detection in Secondary Plastics

Abstract

The systematic identification of impurities inside secondary plastics flow streams can be considered as one of the key issues to certify and to classify waste plastics fed to recycling plants and to perform a full control of the resulting processed fractions, that have to comply with market demands on grade and purity of the recovered products when compared with virgin streams. HyperSpectral Imaging (HSI) can represent an optimal, reliable and low costs answer to reach the previous mentioned goals. HSI is based on the utilization of an integrated hardware and software architecture able to digitally capture and handle spectra, as an image sequence, as they results along a pre-defined alignment on a surface sample properly energized. According to the different wavelengths of the source and the different spectral sensitivity of the device, different physical-chemical superficial characteristics of the sample can be investigated and analyzed. Such an approach, if fully investigated and implemented, could allow to perform a big-step-forward inside quality-inspection-control-strategies/logics (QICSL) applied to the entire waste sector. The identification of contaminants in secondary plastics, adopting HSI, thus can represent a first attempt to introduce new QICSL in an innovative polyolefins separation process from end-of-life product. Such an approach well fit the goals that are at the base of a the application of a non-linear Cyclic Innovation Model (CIM) addressed to connect technical capabilities (contaminants identification) with societal market needs (quality of the recycled products).

PET and PVC Separation with Hyperspectral Imagery

“…Remarkable is the intensive use of the hyperspectral technology in the food sector as a technique for inspection of a wide range of products investigated, such as fruits and vegetables, meat, fish, eggs and cereals [ 22 ]. Recently, several studies have demonstrated that the hyperspectral analysis can be successfully used in the field of solid waste recycling and treatment, with reference to paper [ 23 ], glass [ 24 ], polymers [ 25 ] and polyolefin [ 26 ].…”

Use of Infrared Spectroscopy and Near Infrared Hyperspectral Images to Evaluate Effects of Different Chemical Agents on PET Bottle Surface

“…A number of works have demonstrated the NIR-HSI potential in the polymers field for: crystallinity variations in HDPE (high density polyethylene), LDPE (low density polyethylene) and PP (polypropylene) 23 ; contamination of secondary plastics 24 ; miscibility of poly (3-hydroxybutyrate) blends -PHB and PLA 25 ; classification of polymers (PET and PVC) in different life cycles 26 ; maps of the content of diethyleneglycol (DEG) and terminal carboxylic groups (GCT) in a PET fiber sample; 27 and visualization of hydrolysis in polylactide (PLA) 28 . Although this technique can potentially reveal the distributions of the chemical attack on a polymeric surface, as far as we know, NIR-HSI has not been used to identify areas where the attack has occurred nor to evaluate possible preferential paths for these chemical attacks.…”

Comparison of latent variable‐based and artificial intelligence methods for impurity detection in PET recycling from NIR hyperspectral images

“…There is a vast amount of companies worldwide aimed at recycling PET by already using hyperspectral machinery with NIR and Raman images, together with multivariate models implemented. Many works have dealt with plastic classification by hyperspectral imaging, although only some of them have specially focused on with PET sorting and very few with its separation from PVC …”