FT–Raman investigation of bleaching of spruce thermomechanical pulp

Abstract

Spruce thermomechanical pulp was bleached initially by alkaline hydrogen peroxide and then by sodium dithionite and sodium borohydride. Near-infrared Fourier-transform–Raman spectroscopy revealed that spectral differences were due primarily to coniferaldehyde and p-quinone structures in lignin, new direct evidence that bleaching removes p-quinone structures. In unbleached pulp, the contribution of p-quinones was detected in the 1665–1690 cm–1 region. This contribution was removed to varying degrees in bleached pulps, depending on the extent to which the pulps were brightened. The relative change in the post-colour number of pulp was correlated linearly with the Raman intensity decline in the 1665– 1690 cm–1 region, indicating that p-quinone structures were largely responsible for determining pulp brightness. The 13C nuclear magnetic resonance spectra of milled softwood lignins, obtained to further support the Raman findings, exhibited a peak at ~180 ppm due to quinones. This peak was not detected in the spectra of milled hardwood lignins.

Citation

Agarwal, U.P.; Landucci, L.L. 2004. FT–Raman investigation of bleaching of spruce thermomechanical pulp. Journal of pulp and paper science. Vol. 30, no. 10 (Oct. 2004): Pages 269-274