Does the kappa number method accurately reflect lignin content in nonwood pulps?, 2017PEERS

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 oxidising agent (KMnO4) with lignin and small amounts of other organic functional groups present in the pulp. 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. Contrary to wood lignin, nonwood lignin contains large amounts of hydroxyphenyl (H) monolignol groups, in addition to ferulic and p‐coumaric groups linking the lignin to the hemicellulose matrices. These and other chemical differences will carry through pulping and bleaching processes and will result in a pulp with different oxidizable structures than a pulp sourced from hardwoods or softwoods. Both original data from SFT’s process and kappa and klason data from various nonwood pulp literature sources will be presented to challenge the assumption that the kappa number accurately represents lignin content in nonwood pulps. 

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