Cross-Polarization/Magic Angle Spinning (CP/MAS) 13C Nuclear Magnetic Resonance (NMR) Analysis of Chars from Alkaline-Treated Pyrolyzed Softwood

Pyrolysis chemistry of alkaline-treated loblolly pine is investigated in this study. The pyrolysis experiments were accomplished under an argon atmosphere at 200-400 degrees C, to determine the effect of alkaline treatment on the char formation. Solid-state cross-polarization/magic angle spinning (CP/MAS) C-13 nuclear magnetic resonance (NMR) spectroscopy was used to characterize the chars of the treated and untreated loblolly pine. These studies showed that, in the samples treated with NaOH, there is a shift in the chemical composition of the thermally modified char from cellulosic/hemicellulosic structures to more aryl C structures. At 300 degrees C, carbohydrate peaks were still present in the char of untreated wood but not in the char of the alkaline-treated wood. This indicated that the addition of NaOH enhanced the thermal degradation of the sugars in the pine sawdust. Our studies also showed that there was an emergence of an aliphatic peak around 12 ppm in the treated pine, which is absent in the spectra of the untreated pine. In addition to the relative increase in aryl and aliphatic C species, there is also an increase in the signals seen for the carbonyl species centered around 210 ppm at the higher end of the temperature range in this study for the treated samples. This investigation showed that solid-state NMR provided a facile methodology to investigate the types of changes that occur to wood chars during pyrolysis.