A spectroscopic method for determining lignin content of softwood and hardwood kraft pulps

A rapid method for determining the kappa number of unbleached and oxygen-delignified kraft pulps in the range 3–35 is presented. This novel method was based on the multivariate analysis of VIS spectral data on pulp samples. The calculated models and the test results indicated that partial least squares (PLS) and principal component regression (PCR) models yielded similar results, PLS being slightly more accurate. It was also found that for practical purposes a separate model for each wood feedstock and delignification process is needed.