Corrected steady-state fluorescence emission spectra of various mechanical pulps and celluloses were measured using an excitation wavelength of 320 nm. Regardless of its source, cellulose displayed a relatively high characteristic emission. The emission spectra of mechanical pulps were red-shifted with respect to that of cellulose, and peak shapes were influenced by the pulping process, by hydrogen peroxide bleaching and by monochromatic UV irradiation of the sheets. Changes in emission spectra due to bleaching or UV-irradiation occurred principally in the 370-440 and 500-550 nm regions, and were similar to changes in reflectance spectra reported in the literature. Fluorescence emission spectra of commercial lignins and lignin model compounds were blue-shifted with respect to mechanical pulps, even upon absorption of the fluorophores on solid substrates. Concentration and inner filter effects were evident in emission spectra of commercial lignins, at concentrations as low as 60 ppm. These results suggest that, to a first approximation, emission spectra of mechanical pulps may be interpreted as a decrease in emission of cellulose caused by light absorption by lignin; changes due to bleaching and irradiation may be attributed to changes in lignin absorption.

Gray, Derek G. (Supervisor)