Pressurized hot water extraction of Norway spruce hemicelluloses using a flow-through system

Norway spruce saw meal was extracted with pressurized hot water at 120-240A degrees C using a flow-through system. Only small amounts of hemicelluloses were extracted at 120-160A degrees C, but dissolution was significantly enhanced when higher extraction temperatures were applied. All hemicelluloses but only 15% of lignin were removed from wood at 220A degrees C, and even less lignin was extracted at lower temperatures. Partial degradation of cellulose seemed to take place only at 240A degrees C. Of the total amount of extracted hemicelluloses, 4-22% was hydrolyzed to monosaccharides. Although the average molar masses of extracted hemicelluloses decreased with increasing extraction temperature, even at 240A degrees C the extracted carbohydrates occurred, on average, as polysaccharides. Polysaccharides with an average molar mass of 31 kDa were obtained at 170A degrees C. The molecular-mass characteristics and yield of carbohydrates depend on the extraction temperature, which should be chosen based on the end use of the isolated hemicelluloses.