DEVELOPMENT AND APPLICATIONS OF PYRENE-CONTAINING FLUORESCENT-PROBES FOR MONITORING THE PHOTODEGRADATION OF LIGNIN-RICH PRODUCTS

o-Quinone moieties produced by irradiation of lignin-rich pulp and paper have been selectively derivatized with pyrene moieties following reaction with P(III) compounds. The results of spectroscopic and time resolved emission studies indicate that the tendency for quinone formation upon UV irradiation is enhanced by bleaching processes, specially by oxidative peroxide treatment. In steady state spectroscopic studies pulp fluorescence interferes with excimer emission. However, pulp fluorescence is a very short-lived process (tau less-than-or-equal-to 2 ns), and thus time-resolved spectroscopy can differentiate the two processes readily. These studies show some excimer fluorescence, even under conditions of very low pyrene incorporation. This suggests that o-quinone formation occurs in domains or islands, indicating that degradation occurs predominantly in some regions, or that oxidative degradation processes promote further degradation, perhaps by enhancing oxygen permeability. Fluorescence microscopy studies suggest preferential degradation in fines and fragmented fibers.