Oxidative modifications of cellulose in the periodate system – Reduction and beta-elimination reactions 2nd ICC 2007, Tokyo, Japan, October 25–29, 2007

The conversion of cellulose to dialdehyde cellulose (DAC) by treatment with aqueous periodate was studied by the CCOA method, which is a combination of gel permeation chromatography and carbonyl-selective fluorescence labeling. The beta-alkoxy-elimination reaction under alkaline conditions was used as a diagnostic tool to address the regioselectivity of the oxidation at low degrees of conversion. The oxidation proceeded by random oxidant attack; cluster-like or isolated oxidation patterns were excluded. The beta-alkoxy-elimination proceeded as a competitive process during reduction of DAC by sodium borohydride. Reduction was thus inevitably accompanied by a significant loss in molecular weight. The borohydride treatment decompacted the molecules by reducing the aldehyde groups and destroying hemiacetal crosslinks. As a result, highly flexible chains were produced.

Effect of UV radiation on the carbonyl distribution in different pulps

The effect of UV irradiation on unbleached and TCF-bleached dissolving pulp samples of different provenience, a beech sulphite and an eucalyptus prehydrolysis kraft pulp, has been analyzed according to the CCOA method, evaluating the changes in the molecular weight distribution, the total number of carbonyl groups and the carbonyl group profiles of each pulp. In the case of TCF bleached material, slightly more carbonyl groups were introduced into the kraft pulp as compared to the sulfite pulp. Cellulose degradation was relatively low in both pulps. In the case of unbleached sulfite pulps, the residual lignin had only a minor effect on the molecular weight distribution and the oxidation state of the cellulose, whereas for eucalyptus kraft pulp a pronounced introduction of carbonyl groups accompanied by severe degradation of cellulose was observed. The presence of hemicelluloses governed the photochemical behavior and the carbonyl profiles of the low molecular weight region of the cellulose.