Identification of environmentally degraded microplastics using the thermal-damaged plastics library

, Ikezawa Yoshio.

Microplastics are classified into two types, primary microplastics and secondary microplastics. Primary microplastics refers to substances that are used as law materials in industrial abrasives, scrubbing agents, and so on. Polyethylene (PE) and polypropylene (PP) are frequently used in these applications. Secondary microplastics are usually generated when large plastic products are reduced to a fine size of 5 mm or less by external factors such as ultraviolet radiation in the environment. There are several analytical methods well known in the microplastic researches, and one of them is the Fourier transform infrared spectrophotometer (FTIR). FTIR is generally used in qualitative analysis of plastics and is already utilized in many surveys of the actual condition of microplastic discharges into rivers or sea. However, since actual microplastics are normally degraded in the environment, mainly by ultraviolet radiation, there may be less matches with the infrared spectra referring from a standard FTIR library. Degradation of plastics begins from the formation of carbon radicals with the dissociation of hydrogen from carbon-hydrogen bonds caused by the energy of heat or light. Reaction of the oxygen connecting to those radicals generates different components with bonds like O-H and C=O, which shows specific absorption spectrum. This reaction process causes cross-linking and molecular scission, resulting to the degradation of plastics. Due to the reaction in the plastics, the FTIR analytical result often shows some differences in the infrared spectra between standard plastics and degraded plastics. In order to provide highly reliable identifications, the thermal-damaged plastics library has been introduced and utilized for real microplastics sampled from the environment.

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