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

Abstract

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.

Recent advances in linear and nonlinear Raman spectroscopy. Part VI

“…Loureiro et al . used UVRR microspectroscopy to assess residual chromophores in cellulosic pulps . By monitoring pulp bleaching by UVRR, they found that it is the formation of polysaccharide‐derived chromophores upon bleaching that affects brightness of bleached pulps.…”

Contribution of xylan to the brightness development and stability in the final ECF bleaching of eucalypt (Eucalyptus globulus Labill.) kraft pulp

“…A particular selectivity in the detection and identification of chromophores in pulps is achieved with UV-RR at 325 nm laser beam excitation. This band at 325 nm in the DR spectra corresponds to the absorption of polyunsaturated chromophore structures (Loureiro et al 2011 ).…”

“…Loureiro et al (2010Loureiro et al ( , 2011 showed by UV-RR coupled to UV-vis diffuse reflectance (DR) spectroscopy that xylan is an important source of chromophores in bleached eucalypt pulps. A particular selectivity in the detection and identification of chromophores in pulps is achieved with UV-RR at 325 nm laser beam excitation.…”

“…Conversely, the signals from chromophores of DED xylan bleached with ClO 2 are up-shifted. The signal at ∼ 1627 cm -1 (Table 2) is typical for a more extended chromophoric system, such as the conjugated units bearing aromatic, ethylenic, and carboxylic acid groups (Agarwal et al 2005 ;Loureiro et al 2011 ) present in the DED-D xylan. This is in agreement with the results of Loureiro et al (2010) concerning extracted xylans from fully bleached pulps, where the final ClO 2 treatment increased the amount of conjugated structures in xylan.…”

“…Therefore, it is difficult to develop a defined strategy for the removal of the residual chromophores; brightness development and stability are still insufficient in the final stages of bleaching (Loureiro et al 2011.…”