Tiina Liitiä

Cellulose crystallinity and ordering of hemicelluloses in pine and birch pulps as revealed by solid-state NMR spectroscopic methods

Solid-state 13C NMR spectroscopy was used to determine the degree of cellulose crystallinity (CrI) in kraft, flow-through kraft and polysulphide–anthraquinone (PS–AQ) pulps of pine and birch containing various amounts of hemicelluloses. The applicability of acid hydrolysis and the purely spectroscopic proton spin-relaxation based spectral edition (PSRE) method to remove the interfering hemicellulose signals prior to the determination of CrI were also compared. For softwood pulps, the spectroscopic removal of hemicelluloses by PSRE was found to be more efficient than the removal of hemicelluloses by acid hydrolysis. In addition to that, the PSRE method also provides information on the associations between cellulose and hemicelluloses. On the basis of the incomplete removal of xylan from the cellulose subspectra by PSRE, the deposition of xylan on cellulose fibrils and therefore an ordered ultrastructure of xylan in birch pulps was suggested. The ordered structure of xylan in birch pulps was also supported by the observed change of xylan conformation after regeneration. Similarly, glucomannan in pine pulps may have an ordered structure. According to the 13C CPMAS measurements conducted after acid hydrolysis, the degree of cellulose crystallinity was found to be slightly lower in birch pulps than in the pine pulps. Any significant differences in cellulose crystallinity were not found between the pulps obtained by the various pulping methods. Only in pine PS–AQ pulp, the degree of cellulose crystallinity may be slightly lower than in the kraft pulps containing less hemicelluloses.

13C CPMAS NMR investigations of cellulose polymorphs in different pulps

In order to obtain information about the crystallinity and polymorphs of cellulose, and the occurrence of hemicelluloses in pulp fibers, wood cellulose, bacterial cellulose, cotton linters, viscose, and celluloses in different pulps were investigated by solid state 13C CPMAS NMR spectroscopy. A mixed softwood kraft pulp and a dissolving-grade pulp were treated under strongly alkaline and acidic conditions and the effect on cellulose crystallinity was studied. The presence of different crystalline polymorphs of cellulose and the amounts of hemicelluloses are considered.

A CP/MAS 13C-NMR study of cellulose structure on the surface of refined kraft pulp fibers

The average lateral fibril and fibril aggregate dimensions and the crystallinity of the cellulose in a spruce kraft pulp were investigated by CP/MAS 13C-NMR spectroscopy in combination with spectral fitting. Cellulose isolated by chlorite-delignification and acid hydrolysis from fines fractions enriched in surface material and long fiber fractions enriched in bulk material exhibited no major differences in either lateral dimensions or crystallinity index.

THE INVESTIGATION OF CELLULOSE POLYMORPHS IN DIFFERENT PULPS USING 13C CPMAS NMR

ABSTRACT In order to obtain information about the crystallinity and polymorphs of cellulose and the occurrence of hemicelluloses in pulp fibers, wood cellulose, bacterial cellulose, cotton linter, viscose and celluloses in different pulps were investigated by solid state 13C CPMAS NMR spectroscopy. A mixed softwood kraft pulp and a dissolving pulp were treated under strongly alkaline and acidic conditions and the effect on the cellulose crystallinity was studied. The presence of different crystalline polymorphs of cellulose and the amount of hemicelluloses are considered.