Structural Elements in Native Celluloses

Abstract: In this thesis, a schematic model for the structure ofaggregated cellulose I fibrils is proposed. The model consistsof a crystalline fibril core surrounded by less orderedcellulose forms. These cellulose forms are fibril surfacesaccessible to water, fibril surfaces inaccessible to water andpara-crystalline cellulose. The inaccessible surfaces and thepara-crystalline cellulose are mainly induced byfibril-to-fibril contacts in fibril aggregates.The model is the result of studies by CP/MAS13C-NMR (Cross-Polarisation Magic Angle SpinningCarbon-13 Nuclear Magnetic Resonance) spectroscopy of a largevariety of cellulose materials, e.g. from algae, tunicate,cotton linters, birch pulp, spruce pulp and wood. In addition,the cellulose materials were chemically and mechanicallytreated to expand the sample set. Because of severelyoverlapping signals in the NMR-spectra, a spectral fittingmethod was developed and used to resolve and quantify thesignals. NMR-experiments, such as solvent exchange,spin-lattice relaxation time (T1) and spin-diffusion measurements, were performedin order to assign these signals to the different celluloseforms. From NMR-spectra and the results of the spectralfitting, a multivariate calibration model was constructed whichwas shown to be a possible model to quantify the differentcellulose forms in complex cellulose materials.Keywords:cellulose I, accessible fibril surfaces,inaccessible fibril surfaces, para-crystalline cellulose,fibril aggregates, CP/MAS13C-NMR spectroscopy, spectral fitting, PCA,PLS.