UV-resonance Raman micro-spectroscopy to assess residual chromophores in cellulosic pulps



Ultraviolet-resonance Raman (UV-RR) micro-spectroscopy is an appropriate and sensitive tool to assess the chromophore structures in bleached cellulosic pulps used for papermaking. The particular selectivity in detection and identification of chromophores in pulps is achieved by acquiring the UV-RR spectra in the solid state with laser excitation at 325 nm. This wavelength corresponds to absorption of poly-unsaturated chromophore structures in partially bleached/fully bleached pulps, and linearly correlated with the signal at ca 1600 cm−1 in the UV-RR spectra. The characteristic vibrations from particular pulp chromophore structures have been assigned from experiments with model compounds, thus allowing the establishment of a UV-RR database. Among the components of bleached pulp, the xylan–lignin complex was suggested to be an important source of chromophores. The monitoring of pulp bleaching by UV-RR allowed us to suggest that it is the formation of new polysaccharide-derived chromophores upon bleaching that hinders development of further brightness and is co-responsible for the brightness reversion of fully bleached pulps. Copyright © 2010 John Wiley & Sons, Ltd.