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Appl Environ Microbiol. 1994 May; 60(5): 1395-1400
Copyright © 1994, American Society for Microbiology. All Rights Reserved.

Effect of Residual Lignin Type and Amount on Bleaching of Kraft Pulp by Trametes versicolor

Pulp and Paper Research Institute of Canada, Pointe Claire, Quebec, Canada H9R 3J9

ABSTRACT

The white rot fungus Trametes (Coriolus) versicolor can delignify and brighten unbleached hardwood kraft pulp within a few days, but softwood kraft pulps require longer treatment. To determine the contributions of higher residual lignin contents (kappa numbers) and structural differences in lignins to the recalcitrance of softwood kraft pulps to biobleaching, we tested softwood and hardwood pulps cooked to the same kappa numbers, 26 and 12. A low-lignin-content (overcooked) softwood pulp resisted delignification by T. versicolor, but a high-lignin-content (lightly cooked) hardwood pulp was delignified at the same rate as a normal softwood pulp. Thus, the longer time taken by T. versicolor to brighten softwood kraft pulp than hardwood pulp results from the higher residual lignin content of the softwood pulp; possible differences in the structures of the residual lignins are important only when the lignin becomes highly condensed. Under the conditions used in this study, when an improved fungal inoculum was used, six different softwood pulps were all substantially brightened by T. versicolor. Softwood pulps whose lignin contents were decreased by extended modified continuous cooking or oxygen delignification to kappa numbers as low as 15 were delignified by T. versicolor at the same rate as normal softwood pulp. More intensive O₂ delignification, like overcooking, decreased the susceptibility of the residual lignin in the pulps to degradation by T. versicolor.

^* Corresponding author. Mailing address: Pulp and Paper Research Institute of Canada, 570 St. John's Boulevard, Pointe-Claire, Quebec, Canada H9R 3J9. Phone: 514-630-4100. Fax: 514-630-4134. Electronic mail address: reid@paprican.ca.

This article has been cited by other articles:

• Reid, I. D. (1998). Fate of Residual Lignin during Delignification of Kraft Pulp by Trametes versicolor. Appl. Environ. Microbiol. 64: 2117-2125 [Abstract] [Full Text]