Comparison on the effectiveness of Fourier transform infrared (FT-IR) and attenuated total reflection Fourier transform infrared (ATR-FT-IR) in characterizing plastics biodegradation by insect larvae

Abstract

The discovery that insect larvae can feed on foam plastics provided new exploration ideas and potential for plastic wastes biodegradation. In previous studies, both attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FT-IR) and conventional FT-IR have been used but no comparison has been done to evaluate the difference of effectiveness for the characterization of oxidization and biodegradation of plastics by insect larvae. To address this, foam plastics of polystyrene, polyurethane and polyethylene, as well as the frass of plastics-fed superworms Zophobas atratus were characterized using both FT-IR and ATR-FT-IR, and the differences were compared. For FT-IR, spectra were found to vary due to the difference in shape and thickness of the samples, as well as the moisture absorption of KBr. For ATR-FT-IR, although tests could be performed directly without pretreatment, the reflection with short wavelength could not deeply penetrate into the frass samples. Since the composition of plastics-fed larval frass is more complex than the original plastics, the spectra of FT-IR and ATR-FT-IR were observed significantly different. Therefore, the ATR-FT-IR was more effective in monitoring functional groups of original plastics, and be recommended to employ in combination with FT-IR for a more comprehensive characterization of plastics-fed larval frass in future studies.