Understanding Factors Contributing to Low Oxygen Delignification of Hardwood Kraft Pulps

Abstract

We observed that the O₂ delignification pattern of aspen kraft pulps was distinctly different from that of pine pulps based on a reduction in the apparent pulp kappa number. Much of this phenomenon can be attributed to the variation of the residual extractives and hexeneuronic acid (HexA) unit content in the unbleached and O₂‐delignified pulps, as they interfered with the conventional lignin determination methods. However, after a correction for contributions from these non‐lignin components, the hardwood kraft pulps still displayed a lower response to O₂ delignification than the pine pulps. It appears that the relative reactivity of residual lignin in the hardwood and softwood pulps differs appreciably with the extent of kraft delignification, and is a significant factor affecting the overall O₂ delignification reaction.

Keywords:

• Residual extractives
• hexeneuronic acid
• kraft pulps
• oxygen delignification
• kappa number
• lignin determination

This article is dedicated to the memory of Professor Josef S. Gratzl, a world‐renowned scientist and a good friend.