Raman Spectral Features Associated with Chromophores in High-Yield Pulps

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Abstract
High-yield pulp chromophores are not easily analysed. In Raman spectroscopic studies, advantage can be taken of the fact that chromophores absorb visible light, and they are therefore expected to result in manifestation of the resonance Raman effect. In this effect, the Raman scattering coefficient depends upon the wavelength used to excite the spectrum. The contribution of chromophores in the spectra of mechanical pulps was identified by recording Raman spectra excited at two different 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 evidence of the presence of the chromophores and useful indicators of the extent to which the chromophores were present in the mechanical pulps. 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 completely removed by the bleaching processes.