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Raman spectroscopy was used to study the effects of heat and light treatments on unbleached and peroxide-bleached mechanical and chemimechanical pulps. For bleached mechanical pulp, spectral changes were associated with the removal of coniferaldehyde structures in lignin. In contrast, chemimechanical pulping not only degraded coniferaldehyde units but also partially degraded coniferyl alcohol groups. Furthermore, spectral evidence supported formation of chromophores during chemimechanical pulping; bleaching removed chromophores from chemimechanical pulp. Investigation of unbleached and bleached chemimechanical pulps at 514.5 and 647.1 nm excitation wavelengths revealed a decline in intensity upon the longer wavelength excitation for certain bands, indicating the presence of residual chromophores and suggesting the presence of coniferaldehyde structures. Spectra of lightand heat-treated pulps displayed intensity changes at 1120, 1595, 1620, and 1654cm~1, which were found to be due to the involvement of coniferaldehyde and/or coniferyl alcohol structures in lignin. The most informative Raman band was at 1654cm" 1 . Although newly formed chemical groups/structures due to heat and light treatments could not be identified, new Raman contributions were detected in the lignin aromatic-stretch region. The effects of light or heat were compared in single and sequential treatments. In most cases, the second-stage treatment caused spectral changes that were significantly different from those resulting from direct treatment of pulp, indicating that the effect of the second stage depended on the chemical changes induced in the first stage. For unbleached mechanical and bleached chemimechanical pulp, the order of the single light and heat treatments was found to be important. The sequence of light followed by heat (light-heat) caused more decay in the intensity of the 1654cm" 1 band than did the opposite sequence (heat-light). In contrast, for bleached mechanical and unbleached chemimechanical pulp, similar changes were detected in the 1654cnT 1 band intensity upon sequential treatment. Raman information on treated pulps was correlated with the results of a previous UV-VIS reflectance study. In general, similarity of spectral changes (in the 370nm region) among various pulps and treatments did not necessarily indicate similarity between chemical changes in the pulps. The results seem to suggest significant variation at the molecular level among the responses of pulps for a given treatment and among the treatments for a given pulp.

Summary Ozonations of methylpyranosides, as model compounds for cellulose, were performed in unbuffered aqueous solution at room temperature. The degradation of the pyranosides was followed spectrophotometrically and with high-performance liquid chromatography (HPLC) as a function of ozonation time. The substrates studied were the α- and β-anomers of methyl-D-glucopyranoside, methyl-D-mannopyranoside and methyl-D-xylopyranoside. Methyl-α-D-xylopyranoside degraded more slowly than the other compounds, whereas the rate of degradation was fastest for methyl-β-D-mannopyranoside. In general the degradation of the α-anomers was slower than that of the corresponding β-anomers. HPLC and gas chromatography—mass selective (GC-MS) analyses of the ozonated glucopyranoside samples showed that monosaccharides, lactones, furanosides and acidic compounds are formed during ozonation. A lignin-carbohydrate complex (LCC), containing a D-xylose unit connected to an aromatic part through a βglycosidic bond, was used as a model compound for lignocellulosic pulp. The degradation of this compound during ozonation was also investigated. The results from UV analyses showed that the reaction was extremely fast at the beginning and that the degradation of benzene structures in the lignin mimicking part of the LCC was very rapid. The degradation of the carbohydrate part was slower. This suggests that lignin provides some protection for the cellulose in lignin-containing pulps against attack by ozone. IR and NMR analyses of the freeze-dried ozonated LCC samples showed further that C=O structures are produced during ozonation.

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