Chemical Functionalization and Characterization of Cellulosic Materials

Licentiatavhandling, 2011

Polysaccharides are the most abundant biopolymers produced in nature and belong, together with proteins and nucleic acids, to the main components of life. Polysaccharides are polyhydroxylic polymers that can be functionalized by a wide selection of chemical reactions, and modifications of these biopolymers are applicable in the development of new materials. Such materials, originating from a renewable source are, in principle, in agreement with a sustainable development and are of interest in many different areas of industrial application. The work presented in this thesis is divided into two parts. The first part considers chemical crosslinking of softwood kraft pulp. Fibers were crosslinked with different diepoxides to stabilize the fiber walls and decrease the wet fiber flexibility. The results strongly indicated successful crosslinking reactions. The modified pulps consistently proved to have decreased water retention values and fiber networks formed by the modified fibers possessed an improved ability to resist pressure in the wet state, i.e. a higher wet bulk. These results point to stabilized fiber walls with more rigid structures and consequently, confirm that wet fiber flexibility influences the bulk of fiber networks. In the second part, cationic modified nanocrystalline cellulose, cotton linters and softwood kraft pulp were prepared and characterized using high resolution solution-state nuclear magnetic resonance (NMR). The cellulosic samples were modified with the cationic epoxide 2,3-epoxypropyltrimethyl ammonium chloride under heterogeneous conditions prior to acid hydrolysis and ion exchange solid phase extraction-column purification. The isolation of the cationic modified monomers opened for NMR characterization also at low degrees of substitution. Information on the substituent pattern could be distinguished from the analyzing method. The 2D correlation NMR spectra demonstrated a consistent 9 ppm change in the initial shifts of carbons adjacent to substituted hydroxyl groups and it was concluded that substitution occurs primarily at positions 2 and 6 for all types of cellulosic materials.