Characterization of Alkali Soluble Fraction of Steam Exploded Birch Wood

Birch wood chips, with or without peroxyacetic acid pretreatment, were subjected to steam explosion treatment at 160, 220 and 250°C for different periods of time to reach the same severity or P-factor values (1000, 15,000 and 96,000 min) at each temperature. The exploded pulp was subsequently extracted with water and a 0.4% alkali solution. The alkali soluble fraction was studied by means of elemental, methoxyl analysis, conductometric titration, 1 H-, quantitative 13 C-NMR and FTIR spectroscopy, and gel permeation chromatography methods. With an increasing P-factor value, the polysaccharide content of the alkali soluble fraction decreases rapidly, the syringylpropane unit and aliphatic OH-group concentration decreases, the phenolic OH-group concentration increases, lignin side chains are subjected to oxidation and partial destruction, and pseudolignin is incorporated into lignin macromolecules. The increase in temperature at equal severity of steam explosion has some effect on the removal of the syringylpropane units and on pseudolignin formation. Peroxyacetic acid pretreatment does not have a pronounced effect on the structure of alkali soluble compounds