Volume 1, Number 6
Dec 1993

Determining Kappa Number of Paper

Kappa number is normally found for pulp, not paper. However, the ISO permanent paper standard (ISO 9706, approved in 1993) calls for a kappa number determination as a measure of the amount of lignin in the paper, since a maximum of 1% lignin is allowed. As a guide to this unusual procedure, Annex A is appended to the standard and forms an integral part of it.

Annex A is reprinted below from the prepublication Draft International Standard, with permission. It can be used in connection with either the ISO standard or the ANSI/NISO standard.

Special instruction for determining the kappa number

Since the sole purpose of the kappa number determination is to ascertain whether the kappa number is less than 5.0 or not, it is convenient to adjust the size of the sample taken for analysis so that the sensitivity of the test is at a maximum in the range near kappa number 5. For an oven-dry pulp this sample size is 10 grams. For paper, the sample size should equally be 10 grams. The determination will then be exact if the paper has a kappa number in the approximate range 3 to 7, because ISO 302 requires that between 30 and 70% of the permanganate added should be consumed. If more than 70% or less than 30% of the permanganate is consumed, it is sufficient for the purpose of this International Standard to report the kappa number as >7 or <3 respectively.

NOTE 1 - ISO 302 is intended for the testing of pulp. For the purpose of this International Standard the procedure described in ISO 302 is applied to paper with no modifications. However, with some coated papers containing starch it may be difficult to detect the end point of the titration visually. In such cases an electrometric end-point detection may be used.

NOTE 2 - If the kappa number is determined to be <3 or >7, the determination is not exact, although it is valid for the present purpose. If an exact determination in these cases should be asked for, a new determination with an adjusted sample size must be conducted.