Quantification of photooxidative defects in weathered microplastics using¹³C multiCP NMR spectroscopy

Abstract

We demonstrate an efficient strategy to characterise weathering-induced photooxidative defects in microplastics. The central 13C cross polarisation NMR spectra offer high resolution and are quantitative when combined with multiple excitation.

Quantifying the fragmentation of polypropylene upon exposure to accelerated weathering

“…The contact time was set to 2.0 ms, and the same Hartmann-Hahn conditions as for the multiCP experiments were used. MultiCP measurements [43] were conducted for the longest weathered sample. The parameters for the multi-pulse CP measurements [42] were optimized for the PP samples.…”

“…Additionally, solid-state 13 C magic-angle spinning (MAS) NMR spectroscopy was performed for identification and quantification of photooxidative defects accumulating with proceeding degradation. As previously reported [5,41] quantification is enabled by a multiple cross polarization (multiCP) pulse sequence [42,43]. Although solid-state NMR spectroscopy has rarely been considered for investigation of degradation products, it serves as a complementary method to other commonly used techniques, such as Fourier transform infrared (FTIR) or Raman spectroscopy, and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) [23,24,28,29,[44][45][46].…”

Quantifying the Fragmentation of Polypropylene upon Exposure to Accelerated Weathering

“…Additionally, solid-state 13 C Magic-Angle Spinning (MAS) NMR spectroscopy was performed for identi cation and quanti cation of photooxidative defects accumulating with proceeding degradation. As previously reported (5,43) quanti cation is enabled by multiple cross polarization (multiCP) pulse sequences (44,45). Although solid-state NMR spectroscopy has rarely been considered for investigation of degradation products, it serves as a complementary method to other commonly used techniques, such as Fourier Transform Infrared (FTIR) or Raman spectroscopy, and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) (25,46,31,47,30,48,26).…”

“…Solid-state 13 C CP MAS NMR spectroscopic experiments were performed analogous to (5) for a series of PP samples with different weathering times while multiCP measurements (45) were conducted for the longest weathered sample. The parameters for the multi-pulse CP measurements (44) were optimized for the PP samples.…”

“…They were assigned to the degradation products of PP depicted in Figure S6, as ketones (209 ppm), carboxylic acids (179 ppm), peroxides (85 ppm) and alcohols (74 ppm) (57,58) . Quanti cation was achieved by calibrating the CP spectra to a quantitative multi-CP experiment, as previously described (45). The proportions of the chemical groups are displayed in Figures 4C and 4D.…”