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Two different approaches for the isolation of xylan from hemicelluloserich 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 8C, 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 g/mol could be obtained from oat spelts. The arabinoxylans contained 8-10 mol-% arabinofuranose 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.

The hot water (HW) extraction of Norway spruce (Picea abies [Karst.]) delivers condensed tannins and considerable amounts of other compounds. Yield and composition of the HW extracts were investigated as a function of natural weathering for up to 15 months. Total phenol monomers and oligomers were detected by Folin-Ciocaltau assay after fractionation by solid phase extraction (SPE). Procyanidins (PC) were determined by HPLC-UV after acid thiolysis and carbohydrates by HPLC combined with acid hydrolysis. Topochemistry of the bark before and after extraction was investigated by UV-microspectrometry (UMSP) and non-extractable PC analyzed by direct thiolysis on the bark. The influence of the parameters on the yield and composition of the extracts were evaluated, such as the extraction temperature, time and the addition of sodium sulfate and urea. Prolonged weathering resulted in a considerable decrease of the total extraction yield, partly because of leaching of phenolic monomers, mono- and oligosaccharides. The yield of phenolic oligomers also decreased at a moderate rate, while the yield of polysaccharides (pectins) was almost stable. Non-extractable and non-leachable compounds deposited in the cell lumens represent the majority of the phenolic extractives in spruce bark. Sequential extractions performed at increasing temperature proved to be a suitable method for the recovery of tannin-rich extracts.

Different paper-grade pulps were extracted with nitren, NaOH and KOH in order to produce dissolving pulps and polymeric xylan. The yield and structure of the isolated nitren and alkali xylans were investigated by carbohydrate analysis, HPSEC and 1 H-NMR spectroscopy. In addition the effect of washing stages on the residual nickel content of the nitren xylans was investigated. By nitren extraction up to 98% of the xylan could be extracted out of the fully bleached eucalyptus and birch kraft pulps. The nitren extracted kraft xylans had DP values between 95 (birch) and 111 (eucalyptus). At most 5 mol% of the xylose units were substituted. In the case of pulps with low mannan content only marginally differences between the nitren and alkaline (KOH, NaOH) extractions occurred. The extraction of the relatively ''mannnan rich'' pulps of this study like softwood kraft and beech sulfite pulps revealed that the dissolution effect regarding mannans increased in the following order: nitren < KOH < NaOH. In general the nitren extractions required a lower chemical charge compared to the alkaline extractions, in order to yield similar amounts of xylans. On the other side the necessity of an effective nickel removal is a disadvantage of the nitren extractions.

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