Abstract
This paper describes a method that can be utilized for pre-sorting in chemical recycling processes. Namely, the blend ratios of polymers are determined by employing a low-cost near-infrared (NIR) spectrometer and a spectral deconvolution technique called the classical least squares (CLS) method. The determination of the blend ratio of polymer blends by CLS assumes that the raw material composition of the post-consumer or post-industrial materials is often not completely unknown; rather, it is generally partially known or can be reasonably inferred thanks to prior knowledge of product specifications or manufacturing processes. In short, we can often use the pure component spectra of the constituents in the polymer samples. The NIR spectra effectively capture the structural features of styrene–butadiene–styrene (SBS)/polyethylene (PE) and polypropylene (PP)/PE blend samples, which are complicated by greatly overlapping peaks arising from the components. The near-infrared (NIR) spectra were then subjected to CLS to obtain so-called concentration profile, e.g., the blend ratio of the polymer constituents, by using pure component spectra of SBS, PE, and PP. The pure component spectra were successfully fitted to the observed NIR spectra of SBS/PE and PP/PE samples and estimated blend ratios were achieved with exceptionally high accuracy thus demonstrating that NIR spectroscopy can be a powerful tool for use in the pre-sorting process.
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