Alterations of plastics spectra in MIR and the potential impacts on identification towards recycling

Abstract

Plastic recycling is mainly limited by their sorting as their natures, forms and formulation are very numerous and most of them are strongly incompatible, leading to poor mechanical properties. Several industrial sorting technologies exist, and others are in development. However, each of them has drawbacks. Especially, NIR-HSI (Near-Infrared Hyperspectral Imagery) is limited by the use of carbon black, mainly as a pigment and UV agent in the case of thermoplastics. MIR-HSI (Mid-Infrared) could be a suitable and viable alternative to resolve this issue. Hence, this work, based on laboratory FTIR-ATR (Fourier-Transform Infrared Attenuated Total Reflection), focuses on possible sources of spectral alteration, which could impair identification of usual polymers using industrial MIR-HSI. It aims to help simple and rapid laboratory characterization and give tools to avoid misidentification or enable specific segregation during industrial sorting. First, acquisition parameters were degraded to simulate those imposed by industrial conditions: short acquisition time, diminished resolution and blank defaults. Then, impact on formulations of usual WEEE (Waste of Electric and Electrical Equipment) plastics were evaluated, with PE, PP, ABS and HIPS as matrices, and carbon black (at different concentrations), calcite, talc, titanium oxide and some flame retardants as additives. Several patterns found in homemade standard samples were recognized within a stock of about one hundred of real waste samples.

Analysis of the global market of technologies in the field of collection, sorting and recycling of polymer waste

“…C. Signoret, A. S. Caro-Bretelle, J. M. Lopez-Cuesta, P. Ienny, D. Perrin, L. Milios, L. Holm Christensen, D. McKinnon, M. K. Rasch, M. Hallstrom Eriksen agree that the sorting process causes the most problems [8], [9]. Recycling of polypropylene and polyethylene is studied in more details [10].…”

Source separation, transportation, pretreatment, and valorization of municipal solid waste: a critical review

“…The dynamic industrial application of sensor-based indirect automatic sorting techniques is currently studied (Signoret et al, 2020 ), especially for non-ferrous metal and plastic sorting. It is worth mentioning that the industrial identification system for waste sorting must identify the MSW on the high-speed conveyor belt within a few milliseconds; otherwise, the processor would not issue instructions to manipulate the robotic arm or compressed air nozzles for sorting operations.…”

“…Similarly, Signoret et al investigated the separation effect of carbon black, calcite, talc, titanium oxide, and certain flame retardants as additives or fillers based on laboratory FTIR-ATR on plastic waste. However, it cannot be equated with commercially evaluating MIR-HSI (Signoret et al, 2020 ).…”

Accurate Characterization of Mixed Plastic Waste Using Machine Learning and Fast Infrared Spectroscopy

“…are being investigated, but all these solutions require an understanding of the composition of MPW, especially the potential contaminants . Nondestructive methods such as infrared (IR) spectroscopy, X-ray diffraction, and other techniques have been successfully used for the identification of a single plastic component. − Among these methods, IR spectroscopy has gained particular interest because it can provide accurate identification of plastic polymers . However, IR spectra can be obscured for various reasons (i.e., contain systematic errors and noise), which can make spectral identification challenging.…”