A FTIR method for determining the content of hexeneuronic acid (hexA) and Kappa number of a high-yield kraft pulp

Kappa number is a good indicator of chemical demand for bleaching. In the past, it was considered as an indirect measure of residual lignin, but was later realized to depend on both the residual lignin and hexA groups in pulps. Lignin has been characterized by FTIR spectroscopy and the intensity of its characteristic bands has been used to indicate the residual lignin and Kappa number but these previous FTIR methods were not reliable. In the current study, a number of high-yield kraft pulp samples with different Kappa numbers were produced by cooking pine chips in flow-through reactors. Based on the transmission FTIR spectra of dry pulps, a quick and reliable FTIR method was established using a multivariate analysis to take into account all the characteristic bands of lignin and hexA groups for the prediction of Kappa number and hexA content in pulp. The predicted values were found to be highly comparable with the measured values determined in the laboratory.