Extraction of hemicellulosic oligosaccharides from spruce using microwave oven or steam treatment

This paper describes the extraction of hemicellulosic oligosaccharides from spruce, using microwave or steam treatment that can be used for the production of polymers, replacing fossil-based polymers, e.g., hydrogels. The highest yield of oligosaccharides, measured as mannan, was 70% obtained with treatment in the microwave oven at 200 degrees C for 5 min. The amount of oligosaccharides extracted was 12.5 g per 100 g of dry wood. The molecular weights of some selected samples were analyzed using fast protein liquid chromatography and size exclusion chromatography and time-of-flight matrix-assisted laser desorption ionization. Recovered oligosaccharides following steam treatment at 200 degrees C for 2 min had a mean molecular weight of 3400 g/mol with a maximum weight of 12000 g/mol. Higher severity, i.e., increased temperature (>200 degrees C) and residence time, resulted in lower mean molecular weights and yield. Oligosaccharides with higher mean molecular weights were obtained at lower severity, but the yield was considerably lower. The feasibility of using the extracted hemicellulosic oligosaccharides from spruce for the synthesis of hydrogels was demonstrated.