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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.

A naturally decaycd birch stem was investigatcd in order to find an explanation for its light stability and thus also indirectly for the photo-chemical yellowing of mechanical pulps. The results arc compared to those for fresh birch. The dcnsity of the decayed birch was one quarter that of the fresh birch and its luminance value was higher. The chcmical composition of the decayed birch diffcrcd somewhat from that of the fresh birch. Solid state C-13 NMR spectra indicated that the lignin of the decayed birch had a lower acetyl content and a slightly higher content of free phenolic units. Milled wood and enzymatically isolated lignins from the fresh and decayed birchwoods wcre investigated. The results indicated that the decayed birch lignin contained fewer syringyl units, more -carbonyl groups probably in the carboxylic acid groups. The light stability of the decayed wood can be partly explained by the occurrence of carboxylic acid groups in the -position of the lignin side chain and by assuming that the groups that are easily yellowed photochemically dissolve during the decay, leaving behind a stable and perhaps more rigid macromolecule.

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