Mechanical pulps, surface lignin content

The quality of eucalypt woods for producing chemical pulps was evaluated using NIR spectra and chemometric methods [124]. NIR spectroscopy was used to predict pulp yield and cellulose content from spectra of powdered wood samples [137]. In another application, in addition to estimating lignin content, NIR spectra were used to quantify hardwood-softwood ratios in paperboard [138]. NIR spectra taken from solid European larch samples subjected to axial bending and compression tests revealed an excellent ability to model the variability of mechanical properties [139]. The study demonstrated that the model is based not only on the measurement of density, but also on surface geometry, composition, and, possibly, lignin content. The authors concluded that NIR spectroscopy shows considerable potential to become a tool for nondestructive evaluation of small clear wood specimens, e.g., increment cores. 

In bulk experiments the interaction between cellulose and hemicellulose is often described as sorption rather than adsorption, implying that xylan may also be embedded into the fibre interior. There is no indication of sorption of xylan into the cellulose beads in our experiments. Such sorption would certainly imply changes in the elective radii of the bead with xylan concentration. It has b n shown in the studies of sorption of xylan on birch kraft pulp that the xylan content on the fibre surfaces is much larger than in the bulk fibres (33). We therefore believe that our experiments are of direct relevance to the adsorption behaviour of xylan in chemical pulps. For mechanical pulps, with large amounts of lignin and extractive material in the surface, the situation will be different. 

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