Multi-level color classification of post-consumer plastic packaging flakes by hyperspectral imaging for optimizing the recycling process

Paola Cucuzza; Silvia Serranti; Giuseppe Capobianco; Giuseppe Bonifazi

doi:10.1016/j.saa.2023.123157

Multi-level color classification of post-consumer plastic packaging flakes by hyperspectral imaging for optimizing the recycling process

Spectrochim Acta A Mol Biomol Spectrosc. 2023 Dec 5:302:123157. doi: 10.1016/j.saa.2023.123157. Epub 2023 Jul 14.

Authors

Paola Cucuzza¹, Silvia Serranti², Giuseppe Capobianco¹, Giuseppe Bonifazi¹

Affiliations

¹ Department of Chemical Engineering, Materials & Environment, Sapienza University of Rome, Rome, Italy.
² Department of Chemical Engineering, Materials & Environment, Sapienza University of Rome, Rome, Italy. Electronic address: silvia.serranti@uniroma1.it.

PMID: 37481925
DOI: 10.1016/j.saa.2023.123157

Abstract

In a circular economy perspective, the development of fast and efficient sensor-based recognition strategies of plastic waste, not only by polymer but also by color, plays a crucial role for the production of high quality secondary raw materials in recycling plants. In this work, mixed colored flakes of high-density polyethylene (HDPE) from packaging waste were simultaneously classified by hyperspectral imaging working in the visible range (400-750 nm), combined with machine learning. Two classification models were built and compared: (1) Partial Least Square-Discriminant Analysis (PLS-DA) for 6 HDPE macro-color classes identification (i.e., white, blue, green, red, orange and yellow) and (2) hierarchical PLS-DA for a more accurate discrimination of the different HDPE color tones, providing as output 14 color classes. The obtained classification results were excellent for both models, with values of Recall, Specificity, Accuracy, and F-score in prediction close to 1. The proposed methodological approach can be utilized as sensor-based sorting logic in plastic recycling plants, tuning the output based on the required needs of the recycling plant, allowing to obtain a high-quality recycled HDPE of different colors, optimizing the plastic recycling process, in agreement with the principles of circular economy.

Keywords: Circular economy; Color sorting; HDPE; Hierarchical model; Hyperspectral imaging; Machine learning; PLS-DA; Plastic waste; Recycling.