CP MAS 13C NMR Spectroscopy in Determination of Species-Specific Differences in Wood Composition

In recent years, solid-state C-13 NMR spectroscopy using the techniques of cross-polarization (CP) and magic angle spinning (MAS) has been used to analyze plant materials, including wood. The composition, structure, and behavior of wood components determine the properties of wood materials in various conditions and are therefore important to know. In this work, differences in wood composition were studied for several tree species of central Russia (birch, aspen, spruce, and larch) by CP MAS C-13 NMR spectroscopy. Peaks of CP MAS C-13 NMR spectra were assigned to the main components of the wood. Cellulose was shown to occur in amorphous and crystalline forms; the presence of lignin was unambiguously confirmed by signals from aromatic carbon atoms; and hemicellulose was detected by signals from carbon atoms of the methyl groups of acetylxylose and L-rhamnose. Integral intensities were used to estimate the total proportion of cellulose and hemicellulose in relation to lignin. The lignin content in wood was observed to be maximal in the coniferous species (spruce and larch) and minimal in the deciduous species (aspen and birch).