Changes in fiber ultrastructure during various kraft pulping conditions evaluated by 13C CPMAS NMR spectroscopy

In order to obtain information about the correlation of cellulose fibril aggregate size with the macroscale properties of the wood pulp fibers, three kraft cooking methods with widely varying cooking conditions were used to produce kraft pulps having significantly different physical properties. Variations in cooking conditions included different cooking temperatures, and changes in alkalinity and sulfidity levels. The ultrastructure of these kraft pulps was analysed using 13C CPMAS NMR spectroscopy. From measured spectra cellulose fibril aggregate sizes were determined by means of deconvolution. It was observed that changes in kraft pulping conditions have effect on aggregate size in studied pulps. No clear correlation however between aggregate sizes and physical properties of the pulps was observed.