This study focuses on understanding the physicochemical properties of cellulose as it undergoes the oxygen delignification process. Cellulose contributes to fibre strength but is degraded by oxygen attack. Four different types of cellulose, namely a fully bleached softwood pulp (Q-90), hemicellulose reduced pulp derived from Q-90, cotton cellulose and microcrystalline cellulose (Avicel), were subjected to pressurised oxygen and nitrogen treatments in a kettle reactor. The changes in relative degree of crystallinity, viscosity and carboxylic acid content as a function of time were used to evaluate cellulose degradation. X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy and 13C solid state nuclear magnetic resonance (NMR) spectroscopy determined the relative degree of crystallinity. Viscosity and conductometric titration measurements followed the changes in the degree of polymerisation and carboxylic acid content respectively. A plot of relative degree of crystallinity as a function of oxidation time showed reproducible and consistent results for all celluloses with all applied techniques. The relationship showed a common trend wherein three phases were apparent: an initial increase in relative degree of crystallinity was followed by a decrease and then another gradual increase. The change from a decrease in relative degree of crystallinity to an increase occurred at fifteen minutes for Q-90 and hemicellulose reduced pulp, and at minutes for cotton cellulose. No change in the relative degree of crystallinity with time was evident for Avicel. These trends were rationalised using the concept of the fringed micelle model.

Argyropoulos, Dimitris S. (Supervisor)