Xylans from oat spelts and birch kraft pulp

Two different approaches for the isolation of xylan from hemicellulose-rich sources have been investigated: Alkaline extraction from roller-mill pretreated oat spelts and Nitren extraction of birch kraft pulp. For xylan recovery from oat spelts the experiments included extraction with 5% NaOH at 90 degrees C, followed by precipitation in methanol or 2-propanol without neutralisation in order to facilitate NaOH recovery. A subsequent peroxide bleaching yielded a product of approximately 90% ISO brightness. The work on Nitren extraction of birch kraft pulp included the optimisation of the extraction process with regard to the Nitren charge. Nitren was much more specific in xylan extraction compared to Cuen, and up to 90% of the xylan content of the birch kraft pulp could be removed. it turned out that dried pulps were superior for this process compared to never-dried pulps, since substantial cellulose proportions in never-dried pulps were also mobilised by Nitren treatment. The properties of the recovered xylans from both processes were compared with regard to molar mass and substitution. It could be demonstrated that more or less intact arabinoxylans with molar masses Of 30,000 9/mol could be obtained from oat spelts. The arabinoxylans contained 8-10 mol-% arabincifuranose and 2 mol-% 4-O-methylglucuronic acid substituents. Nitren extraction of a birch kraft pulp yielded xylans of 9,400 and 11,200 g/mol. Only traces Of 4-O-methyl-glucuronic- and hexenuronic acid substituents could be found.