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Abstract
Previously, it was shown that chlorine dioxide delignification (D0) modifies kraft residual lignin by oxidizing phenolic groups to both quinonoid and muconic structures in ∼2‐to‐1 ratio (1.7 mmol/g lignin vs. 0.8 mmol/g lignin), respectively. Alkali extraction (E), in addition to removing solubilized lignin and saponifing muconic acid methyl esters, re‐activates the residual D0 lignin towards ClO2 oxidation by converting quinones to polyphenols. This action of alkali on D0 oxidized lignin is analogous to that of hydrosulfite reduction (Y). Chlorine dioxide oxidation of D0E and D0Y treated pulps generally afforded ∼1.7 mmol quinones/g lignin onto the oxidized lignin, like that of the D0 stage. This study clearly indicates that quinones formed during the D0 stage can be easily re‐activated toward ClO2 oxidation in a D1 by alkali treatment, such as an E stage.
#Dedicated to Drs. Donald R. Dimmel and Thomas J. McDonough on their retirement from the Institute of Paper Science and Technology.
Acknowledgments
The authors would like to thank the Analytical Group at the Institute of Paper Science and Technology (IPST) at Georgia Tech for their assistance with various analyses. A special thanks goes to Robbie Hannah at Sappi, who performed the pilot digester cooks of the black spruce employed in this study, and to Dr. Alan W. Rudie of the USDA Forest Products Laboratory for his critical review of this research. Portions of this work were used by D. G. Mancosky as partial fulfillment of the requirements for the Ph.D. degree at IPST. Parts of this work were presented at the 2002 International Pulp Bleaching Conference in Portland, OR.
Notes
#Dedicated to Drs. Donald R. Dimmel and Thomas J. McDonough on their retirement from the Institute of Paper Science and Technology.