Kappa number

The Kappa number is an indication of the lignin content or bleachability of pulp. It measures the amount of bleach required during digestion of a wood pulp (part of the process of paper making) in order to obtain a pulp with a given degree of whiteness. Since the amount of bleach needed is related to the lignin content of the pulp, the Kappa number can be used to monitor the effectiveness of the lignin-extraction process. The number is in the range of 1-100 (10-70 for most types of wood) and is established by measuring the amount of a standard potassium permanganate solution that is absorbed by the pulp being considered. Details on how the Kappa number should be determined is published in ISO 302:2004.