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Mid-Infrared Spectrometer for Black Plastics Sorting Using a Broadband Uncooled Micro-Bolometer Array
Summary
This paper describes a mid-infrared spectrometer built around an uncooled sensor array that can instantly analyze plastics across a broad wavelength range — including black plastics that standard near-infrared sorters cannot identify — making it suitable for handheld, battery-powered recycling devices. While the tool is relevant to plastic waste sorting and recycling infrastructure, the paper does not address microplastic pollution directly. It is more relevant to improving plastic recycling than to environmental microplastic contamination.
We report the design, implementation and test of a Mid-Infrared spectrometer proof-of-concept that utilizes an uncooled micro-bolometer array, sensitive in the 3–14 µm spectral range, integrated in a conventional optical dispersive spectrometry setup. Such a spectrometer enables instantaneous measurements across this broad spectral range, comparable to that of a FTIR but with a more compact design and without moving parts. This makes it ideal for integration into portable, battery-powered devices such as handheld scanners. The Mid-IR range offers significant advantages over NIR-SWIR spectrometers, especially for organic compound analysis. A notable application for this instrument: plastic waste sorting—including black plastics—was tested with significant accuracy and effectiveness of plastic classification (on PP, PET and PE samples) with a very simple machine learning algorithm.