Inhomogeneities in the chemical structure of spruce lignin

Thioacidolysis, periodate oxidation and size exclusion chromatography (SEC) were used for the analysis of spruce lignin samples. The standard thioacidolysis method was modified by including a pre-swelling of the lignocellulosic sample before the reaction, and this gave a higher yield of monomer products. Middle lamella and compression wood lignin was found to contain a larger amount of oligomers after thioacidolysis than normal wood lignin. Analysis by thioacidolysis of a thermomechanical pulp (TMP) revealed that approximately 10% of the beta-O-4 structures in the lignin were cleaved due to the mechanical grinding effect. From kraft pulp, the mixture of thioacidolysis products contains a major fraction having a considerably larger molecular mass than the products from spruce wood and TMP. The structure of this material is still unknown.