Quantum cascade laser-based reflectance spectroscopy: a robust approach for the classification of plastic type

Abstract

The identification of plastic type is important for environmental applications ranging from recycling to understanding the fate of plastics in marine, atmospheric, and terrestrial environments. Infrared reflectance spectroscopy is a powerful approach for plastics identification, requiring only optical access to a sample. The use of visible and near-infrared wavelengths for plastics identification are limiting as dark colored plastics absorb at these wavelengths, producing no reflectance spectra. The use of mid-infrared wavelengths instead enables dark plastics to be identified. Here we demonstrate the capability to utilize a pulsed, widely-tunable (5.59-7.41 µm) mid-infrared quantum cascade laser, as the source for reflectance spectroscopy, for the rapid and robust identification of plastics. Through the application of linear discriminant analysis to the resulting spectral data set, we demonstrate that we can correctly classify five plastic types: polyethylene terephthalate (PET), high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS), with a 97% accuracy rate.

Mid-infrared spectroscopy and machine learning for postconsumer plastics recycling

“…64,65 Due to the nanometer-scale engineering of the device's electronic wavefunctions, desired lasing properties can be achieved and applied to polymer identification sensors. 18,66,67…”

“…13 Consequently, there has been an unprecedented surge of multi-disciplinary research aimed at reducing plastic waste, limiting the production of virgin polymers, and improving pathways for PCPW to re-enter the value chain. [14][15][16][17][18][19][20][21][22][23][24][25][26][27] The development of automated optical sorting technologies for implementation at MRFs is one of these active research thrusts in the plastics recycling community. 28,29 This is because MRFs currently rely on air jets, magnetic separators, mechanical pistons, and human intervention to sort PCPW, all of which are methods that have been deemed insufficient to meet growing recycling demands.…”

Setup and Analysis of a Mid-Infrared Stand-Off System to Detect Traces of Explosives on Fabrics

“…The signals in both spectra overlapped to a great extent, proving that the sample was indeed being detected. Some differences in peak positions and shapes were to be expected due to the different spectra recording methods (scattered reflectance vs. ATR-FTIR) [ 26 ].…”

Short-Pulse Photothermal Modulation of Silicon Optical Cavities Measured by a Continuous Mid-IR Probe

“…The IR source was a mid-infrared quantum cascade laser (MIRcat-QCL) from DRS Daylight Solutions. In the past few years, the quantum cascade laser (QCL) has been utilized in many applications due its many advantages. − With careful engineering of layered quantum wells and using the electron tunneling effect cascading down supperlattices, , QCLs provide high intensity IR laser powers that exceed the limits of other IR sources such as the FTIR glowbar. This IR source can be tuned with a resolution of 0.1 cm –1 from 1500 to 2300 cm –1 .…”