Characterization of hemicelluloses in process streams in thermomechanical and chemi-thermomechanical pulp mills

Increased interest in hemicelluloses as a renewable source of biopolymers has resulted in an interest in hemicelluloses in process streams in pulp mills. The aim of this study was to compare potential positions for the withdrawal of hemicelluloses from mechanical pulp mills. Samples were withdrawn at a total of fourteen positions from two thermomechanical and two chemi-thermomechanical pulp mills. The molecular mass distributions of hemicelluloses and lignin were determined by size-exclusion chromatography. Hemicelluloses showed peaks in the molecular mass interval of 0.2–2 kDa and 4–60 kDa, whereas lignin showed peaks in the range of 0.5–4 kDa, but no peak in the high-molecular-mass region. Glucomannan accounts for approximately two-thirds of the hemicellulose content of softwood, and mannan and glucan were thus the dominating saccharides in all samples. Mannan was preferentially found in fractions with a molecular mass ranging from 4 to 22 kDa