Fig. 5: 1H MAS NMR spectra.

a 1H MAS NMR spectra of the irradiated and non-irradiated altered samples. b 1H MAS NMR spectra of the non-irradiated and altered sample at different spinning frequencies. c 1H MAS NMR spectra of the irradiated and non-irradiated altered samples after heating again at 50 °C. d 1H MAS NMR–Hahn-Echo spectra with varying echo delay of the non-irradiated and altered sample. e 1H MAS NMR–Hahn-Echo spectra with varying echo delay of the irradiated and altered sample.