RAMAN SPECTRAL FEATURES ASSOCIATED WITH CHROMOPHORES IN HIGH-YIELD PULPS

High-yield pulp chromophores are not easily analysed. In Raman spectro scopic studies, advantage can be taken of the fact that chromophores a bsorb visible light, and they are therefore expected to result in mani festation of the resonance Raman effect. In this effect, the Raman sca ttering coefficient depends upon the wavelength used to excite the spe ctrum. The contribution of chromophores in the spectra of mechanical p ulps was identified by recording Raman spectra excited at two differen t wavelengths (514.5 and 647.1 nm). In these spectra, the intensities of certain bands and the band width of the 1595 cm-1 band changed when the wavelength of excitation was changed. These changes were clear ev idence of the presence of the chromophores and useful indicators of th e extent to which the chromophores were present in the mechanical pulp s. Spectral contributions due to chromophores were found at 1120, 1595 , 1620, and 1654 cm-1. Raman studies of bleached pulps were consistent with these observations and indicated that chromophores were not comp letely removed by the bleaching processes.