MIR spectral characterization of plastic to enable discrimination in an industrial recycling context: I. Specific case of styrenic polymers

Abstract

One of the major limitations in polymer recycling is their sorting as they are collected in mixes. The majority of polymers are highly incompatible without compatibilizers. For sorting of polymers, high-speed online Near-Infrared (NIR) spectroscopy is nowadays relatively widespread. It is however limited by the use of carbon black as a pigment and UV-stabilizer, which strongly absorbs near-infrared signals. Mid-Infrared (MIR) hyperspectral cameras were recently put on the market. However, their wavelength ranges are smaller and their resolutions are poorer, in comparison with laboratory equipment based on Fourier-Transform Infrared (FTIR). The identification of specific signals of end-of-life polymers for recycling purposes is becoming an important stake since they are very diverse, highly formulated, and more and more used in copolymers and blends, leading to complex waste stocks mainly as WEEE (Waste Electrical and Electronic Equipment). Dark colored plastics are the major part of WEEE, which also contains mainly styrenics (ABS, HIPS and their blends). In addition, styrenics are especially concerned by the need of identification. In this framework, spectral characterizations of ten types of polymers were scrutinized through about eighty pristine and real waste samples. Polymer characteristic signals were aggregated in charts to help rapid and automatized distinction through specific signals, even in limited resolution and frequency ranges.

Keywords: Identification; MIR; Polymer recycling; Sorting; Styrenics; WEEE.