Does the kappa number method accurately reflect lignin content  in nonwood pulps?, TAPPI Journal November 2018

ABSTRACT: The traditional kappa number method was developed in 1960 as a way to more quickly determine the level of lignin remaining in a completed or in-progress pulp. A significantly faster approach than the Klason lignin procedure, the kappa number method is based on the reaction of a strong oxidizing agent (KMnO₄) with lignin and small amounts of other organic functional groups present in the pulp, such as hexenuronic acid. While the usefulness of the kappa number for providing information about bleaching requirements and pulp properties has arguably transformed the pulp and paper industry, it has been mostly developed for kraft, sulfite, and soda wood pulps.

Nonwood species have a different chemical makeup than hardwood or softwood sources. These chemical differences can influence kappa and Klason measurements on the pulp and lead to wide ranges of error. Both original data from Sustainable Fiber Technologies’ sulfur and chlorine-free pulping process and kappa and Klason data from various nonwood pulp literature sources will be presented to challenge the assumption that the kappa number accuately represents lignin content in nonwood pulps.

Application: The information provided in this study closely examines typical results of the analysis of lignin in nonwood pulps and encourages researchers in this area to measure both kappa number and Klason lignin separately to determine if a consistent correlation can be applied.

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