Qualitative Identification of Microplastics: A Preliminary Study Using Fourier-transform Infrared (FTIR) Spectroscopy

The prevailing of microplastics draws a great deal of concern due to their negative impacts to the environment. The environmental microplastics usually consist of several chemical constituents, and classifying these constituents is import for subsequent pollution control and risk management. In the literature the environmental microplastics were often analyzed as a whole by measuring their total weight and particle number. In contrast, this study employed Fourier-transform infrared (FTIR) spectroscopy to identify the polymer constituents of the tested microplastics, using polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and nylon (NY) as the model plastic polymers. Mixtures containing different tested microplastics were analyzed. For a given tested plastic in a plastic mixture, its apparent signals may be interefered or masked by the reflection of another coexisting plastics. Therefore, uniqueness in FTIR signal for each tested plastic becomes critical if each plastic constituent shall be identified. By comparing the FTIR signals from the plastic sample containing multi-component polymers, the characteristic wave number of each test sample was established according to its obtained FTIR spectrum. The FTIR spectra enabled the identification of their respective plastic constituents. In addition, real samples obtained from a selected industry and the ambience were employed to examine the applicability of the proposed identification procedure. This study demonstrated the FTIR application to identifying microplastic constituents by proposing a systematic operating procedure.