Detection of kappa number distributions in kraft pulps using NIR spectroscopy and multivariate calibration

Chemical pulp is characterized by its average lignin content, commonly expressed as the pulp's kappa number. However, this average kappa number provides no information about the distribution of kappa number within the pulp. This study proposes a new method of pulp characterization using near-infrared reflectance (NIR) spectroscopy to measure distributions of kappa numbers within pulp samples. Pure pulps with different kappa numbers were mixed to create blended samples with a known nonuniformity of kappa number distribution. NIR spectroscopy-combined with multivariate calibration methods-was used to detect distributions of kappa numbers in the pulps. Models calculated from these data gave good predictions of the average kappa number as well as the standard deviation around the average. The results imply that NIR spectroscopy can provide information about the average kappa number as well as the distribution of kappa number within the pulp.