A comparative CP/MAS 13C-NMR study of cellulose structure in spruce wood and kraft pulp

CP/MAS C-13-NMR spectroscopy in combination with spectral fitting was used to study the supermolecular structure of the cellulose fibril in spruce wood and spruce kraft pulp. During pulping, structures contributing to inaccessible surfaces in the wood cellulose are converted to the cellulose I beta allomorph, that is, the degree of order is increased. This increase is also accompanied by a conversion of cellulose I alpha to cellulose I beta. Cellulose from wood composed of different cell types, that is, compression wood, juvenile wood, earlywood, latewood and normal wood exhibited a similar supermolecular structure. Assignments were made for signals from hemicellulose which contribute significantly to the spectral C-4 region (80-86 ppm) in kraft pulp spectra but substantially less to the corresponding region in wood spectra.