New Insights into Lignin Modification During Chlorine Dioxide Bleaching Sequences (I): Chlorine Dioxide Delignification

Abstract

Chlorine dioxide delignification (D₀) modifies kraft residual lignin by oxidizing phenolic groups to both quinonoid and muconic structures. Results from various in situ analyses (i.e., kappa/Klason lignin, methanol, and methoxyl group analyses) demonstrated that the D₀ stage preferentially oxidizes phenolic entities to quinones over muconic structures in ∼2:1 ratio (1.7 mmol/g lignin vs. 0.8 mmol/g lignin), respectively. The level of quinones detected by these in situ methods was significantly higher than those determined by the NMR analysis of isolated D₀ residual lignin. It was discovered that the acidic procedure used to isolate the oxidized lignin for NMR analysis chemically eliminated the majority of quinonoid structures, which resulted in lower amounts of quinones detected. This study clearly indicates that quinones are a significant reaction product formed during the D₀ stage.

^#Dedicated to Drs. Donald R. Dimmel and Thomas J. McDonough on their retirement from the Institute of Paper Science and Technology.

Keywords:

• Phenolic groups
• NMR analysis
• Lignin
• Chlorine dioxide delignification
• Kappa number
• Klason lignin
• Kraft pulps
• Bleaching
• Quinones
• Muconic acids

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 the methanol and methoxyl group 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 2003 International Symposium of Wood and Pulping Chemistry Conference in Madison, WI.

Notes

^#Dedicated to Drs. Donald R. Dimmel and Thomas J. McDonough on their retirement from the Institute of Paper Science and Technology.