Solid state NMR studies on cellulose crystallinity in fines and bulk fibres separated from refined kraft pulp

Solid state NMR spectroscopy has been used in this work to investigate crys tallinity of cellulose in spruce mood before and after kraft pulping and TC F bleaching. Effects of refining of the spruce kraft pulp in water and in w eak alkali have been studied by determination of the crystallinity of isola ted fines and corresponding bulk fibres in order to find out whether the cr ystallinity in the fibre surface material and inside the fibre wall differ from each other. Also the possible effect of enzymatic endo-1,4-beta -galac tanase treatment on the crystallinity of some refined pulp has been investi gated. It was found that the I-alpha crystalline form of cellulose predomin ates over the I-beta form in native spruce and ice viceclsa in all the pulp s studied. In pulping part of the cellulose I-alpha is converted to the mor e stable I-beta, form mainly by heat. Any measurable changes in the degree of crystallinity or in the relative proportions of different crystalline fo rms of cellulose could not be seen in pulps after refining, TCF-bleaching o r galactanase treatment. However, the degree of crystallinity was found to be considerably lower in the fines compared to the corresponding bulk fibre s. Therefore it is suggested that the cellulose crystallinity is lower or t he size of crystallites smaller on the fibre surface than inside the fibre wall. Slightly higher contents of lignin and hemicelluloses, mainly xylan a nd mannan, were also found in the fines compared to the bulk fibres.