A Fundamental Reveiw and Critical Analysis of Hexenuronic Acids and Their Impact in Elemental Chlorine-Free Bleaching, 2009 TAPPI Engineering, Pulping, Environmental Conference

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Hexenuronic acids (HexA) has been the subject of much research since the mid-1990s when it was discovered that these functional groups can contribute to the measured kappa number of the pulp, as well as to how a pulp respond to various bleaching agents. The goal of this paper is to review and critically analyze the scientific literature concerning HexA. Most quantification methods utilize UV/Vis spectroscopy, in conjunction to selective HexA hydrolysis, to measure the concentration of these structures in pulp. The strengths and weakness of these methods are discussed.

HexA contributes approximately 15 to 50% of the measured kappa number for most hardwood pulps, as opposed to ¡Â 10% for soft-woods. The formations of these groups, as well as their depletion, during kraft pulping are a strong function of wood species (hard-wood vs. softwood) and effective alkali (EA). The activation energies for HexA generation and removal are similar to those related to bulk delignification and hemicellulose degradation.