Characterization of Lignins from Organosolv Pulping According to the Organocell Process. Part 3. Permanganate Oxidation and Thioacidolysis

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Abstract
Both residual lignins and lignins isolated from the pulping liquor of 20 l batch cookings of spruce chips according to the organocell process were subjected to HPSEC. Checking the resulting Mn-values by vapor pressure osmometry confirmed the HPSEC data except for first stage lignins with short cooking times, where the different elution behavior caused by high portions of organic nonlignin substances is held responsible for these discrepancies. The molecular weights of residual lignins, which were found to be considerably higher than those of the corresponding soluble lignins, are dependent on yields and/or isolation procedure and are therefore not representative of the total lignin in the pulp. The investigation of lignin fractions isolated according to molecular weight by GPC reveals the preferential side chain degradation of the low molecular weight portions, which is explained by the protection of high molecular weight particles within association complexes and/or by specific reactions of structural units, which are typical for low molecular weight lignins.

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