Identification of cast and extruded PMMA for sustainable recycling and using terahertz time domain spectrometer

In 2020, the demand for polymethylmethacrylate (PMMA) boards increased sharply following the spread of COVID-19. There are two types of acrylic panel. Although the cast and extruded PMMA are formed in different ways, they are almost identical in appearance. Therefore, it is difficult to distinguish between the two when they are used and disposed of in the market, and identification is not adequately carried out by waste producers. Moreover, the molecular chains of the cast and extruded plates are different, which means that their melting points are also different. As a result, it becomes difficult for recyclers to implement material recycling if they are disposed of together. Because both cast and extruded boards are used in these partitions, there is an urgent need to establish appropriate identification techniques. In this study, terahertz (hereinafter: THz) waves were irradiated onto cast and extruded plates, and the differences in transmittance and reflectance were analysed to show that the two can be discriminated. By utilising these techniques, it was possible to identify cast and extruded plates and establish a potential method that contributes to the proper recycling of acrylic partitions, as well as to the promotion of material recycling.