Fluorescence emission from mechanical pulp sheets

Abstract

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 owing to bleaching or UV irradiation occurred principally in the 370–440 nm and 500–550 nm regions, and were similar to changes in reflectance spectra reported in the literature. This suggests 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.