Dithionite bleaching of thermomechanical pulp:: factors having effects on bleaching efficiency

The efficiency of dithionite bleaching of Norway spruce (Picea abies) thermomechanical pulp was studied by applying various multivariate data analysis techniques to analytical data (temperature, pH, ion chromatographic and energy-dispersive X-ray fluorescence data). In addition, modeling the residual sulfur content of bleached pulp by means of diffuse reflectance UV-vis spectral data from laboratory-scale bleaching experiments was attempted. The results indicated that this lignin-preserving bleaching process could be evaluated by means of the analytical data using either PCR or PLS models. These models also indicated that wavelengths below 400 nm should not be used in measuring the pulp brightness. The residual sulfur content of pulp could not be reliably determined by multivariate modeling of the diffuse reflectance UV-vis spectral data. Copyright (C) 2000 John Wiley & Sons, Ltd.