HI is attributed to the bond vibrations of hydroxyl, carboxyl, or phenol groups. Conversely, fragments showed greater values of HI (5.90 ± 2.57) and COI (1.04 ± 0.48) than pellets, as well as lines, which presented the maximum value of HI (11.51). This index helps evaluate the degradation of PE MPs by UV light, increasing with enhancing residence time in the environment. On the other hand, fragments presented slicer modifications in the carbonyl region with CI values lower than pellets (0.05 ± 0.05). Most samples (57%) presented a CI with values between 0.16 and 0.30.

On the one hand, the CI calculated for the environmental PE pellets showed values ranging from 0.05 to 0.26 with a mean value of 0.17 ± 0.10. Differences in CI, HI, and COI were evidenced among the different morphological MP shapes. Moreover, new unique peaks were also observed in the freshwater particles, almost all in the fingerprint region (1500–500 cm −1). Otherwise, the following incubation of the same particles at a constant temperature of 45 ☌ did not further affect the chemical composition of the particles. Particular enhancements of CI of PS fragment and PE pellet, HI of PE and PS fragments and PE pellet, and COI of PS fragment were observed. The indexes calculated for polymers degraded under the artificial photo and thermo ageing conditions displayed a general tendency to increase with the time in contact with irradiation time. The overall results showed that the regions reflecting changes (hydroxyl groups, peaks from 3100 to 3700 cm −1, alkenes or carbon double bonds, 16 cm −1, and carbonyl groups, 16 cm −1) appeared significantly modified in artificial and natural weathered particles compared to the pristine materials. The degree of ageing was assessed using three different indexes known to be related to changes in MPs: Carbonyl Index (CI), Hydroxyl Index (HI), and Carbon-Oxygen Index (COI). FTIR spectra were acquired using a Nicolet Summit FTIR (ThermoFisher Scientific) equipped with an Everest ATR with a diamond Crystal plate and a DTGS KBr detector (wavenumber range 4000–500 cm −1, 32 scans per spectrum, spectral resolution of 4 cm −1). Furthermore, we compared environmental particles to weathered artificial MPs under controlled light and temperature conditions and to unaltered pristine materials to assess the results. In this context, the principal aim of our research has been to qualitatively evaluate the natural weathering of environmental MPs collected in an Italian freshwater body (the Ofanto River) using ATR-FTIR technology. However, it could also be used to evaluate the degree of ageing of MPs collected from the environment. It has recently gained popularity in microplastic (MP) pollution research to determine the chemical composition of unknown plastic fragments. Fourier transform infrared (FTIR) is a spectroscopy technique widely used to identify organic materials.

Essential ftir software crack