The depletion of fossil fuels and the need to deal with climate change lead to an increasing interest in renewable resources. Lignocellulosic biomass in general, and agricultural residues in particular, could serve as an excellent starting material for the production of cellulose, basic chemicals, lignin and bioethanol in a biorefinery framework as they are abundant, do not compete with food production and are distributed worldwide. Two factors considerably influence the composition and properties of biorefinery products: biomass feedstock and pretreatment process. Their influence on the separability of raw material into a carbohydrate and lignin fraction as well as the composition and properties of these products are objectives of this study. Hereby, the focus is on lignin, as its structure is particularly dependent on the aforementioned factors complicating its further utilisation. Different agricultural biomass namely barley straw, coconut shell powder, hemp shives, horse manure, maize straw, miscanthus, oat husk, pretreated alfalfa, rape straw, sunflower stalks, tomato stalks and wheat straw were investigated regarding their suitability for lignocellulose separation using alkaline soda pulping. Best separation into a carbohydrate and lignin fraction was achieved for pretreated alfalfa, miscanthus, wheat and barley straw. The purity of the obtained lignin fractions varied in the wide range of 57% klason-lignin content for sunflower stalks and 81% for pretreated alfalfa prior to further purification by dialysis. Lignin fractions were characterised by means of FTIR spectroscopy, elementary analysis, thioacidolysis, size-exclusion-chromatography, thermodesorption, differential scanning calorimetry and different wet chemical methods for determination of functional groups. Lignins could be classified into groups, within which they show similar characteristics: (A) horse manure, rape straw, (B) sunflower stalks, tomato stalks, (C) barley-, maize- and wheat straw and (D) hemp shives, miscanthus. In addition, promising lignin candidates were found for several applications. Thus, by screening different agricultural residues, it is possible to choose a specific raw material, in order to produce lignin with desired properties and functionalities. The effect of the pretreatment process was studied based on wheat straw. It was subjected to conventional alkaline pulping, microwave-assisted alkaline pulping and organosolv pulping using formic acid and hydrogen peroxide. Pulping parameters were varied in order to attain best possible separation into a carbohydrate and lignin fraction. Of the varied parameters the concentration of both sodium hydroxide and formic acid has the highest impact on yield and purity of the products for alkaline and organosolv pulping, respectively. It additionally influences the content of functional groups of the lignin fraction and is hence, an important parameter for lignin customisation for subsequent utilisation. Furthermore, the possibility of reducing pulping time by using microwave-assisted pulping instead of conventional alkaline pulping is promising, as the obtained carbohydrate fraction has a low intrinsic viscosity, which may enhance enzymatic hydrolysis.

Die Festigkeitseigenschaften des Papiers hängen vom Gehalt und der Verteilung der Hemicellulosen über den Querschnitt der Faserwand ab. Hemicellulosen werden durch verschiedene Bleichverfahren unterschiedlich stark angegriffen und herausgelöst. Durch Untersuchungen an einem Fichtensulfitzellstoff ist es gelungen, die Auswirkungen einzelner Bleichstufen [Peroxidverstärkte Sauerstoffstufe (EOP), Ozonstufe (Z) und Peressigsäurestufe (PAA)] und Bleichsequenzen (EOP-Z-P, EOP-PAA-P) auf Faseroberfläche, Hemicellulosenzusammensetzung und -verteilung sowie auf die optischen und mechanischen Eigenschaften des daraus gebildeten Papiers aufzuzeigen. Um die Verteilung der Hemicellulosen über den Querschnitt der Faser zu beschreiben, wird das Verfahren des chemischen Abschälens verwendet und schrittweise die Faserwand entfernt. Der gebleichte bzw. abgeschälte Zellstoff wird rasterelektronenmikroskopisch untersucht, hydrolysiert und anschließend die Hemicellulosenzusammensetzung quantitativ mittels Hochdruckflüssigkeitschromatographie (HPLC) unter Nutzung eines Flüssigkeitsmassenspektrometers (LCMS) als Detektor bestimmt. Zusätzlich erfolgt die Bestimmung der Papiereigenschaften. Diese Untersuchungen bestätigen, dass die verschiedenen Hemicellulosengehalte nach den Bleichstufen Unterschiede bei den Festigkeitseigenschaften bewirken. Die Untersuchungen zeigen den positiven Effekt der Peressigsäurestufe für die Papierherstellung im direkten Vergleich zur Ozonstufe. Zusätzlich wurde auch der Einfluss des Aufschlusses geprüft. Hierzu wurden die endgebleichten Sulfitzellstoffe mit einem endgebleichten Sulfatzellstoff verglichen. / The mechanical strength of paper pulp depends strongly on the hemicellulose content and the hemicellulose distribution across the cell wall layers. Hemicelluloses get differently attacked and dissolved by different bleaching methods. The investigations with a paper grade sulphite pulp show the influence of the separate bleaching steps [hydrogen peroxide reinforced oxygen stage (EOP), ozone (Z) und peracetic acid (PAA)] and bleaching sequences (EOP-Z-P, EOP-PAA-P) of the fibre surface, hemicellulose content and distribution as well as the optical and mechanical characteristics of paper. To describe the hemicellulose distribution across the cell wall layers a procedure of a precise chemical peeling was used in order to remove stepwise the cell wall. The bleached and peeled pulp was investigated by scanning electronic microscope (SEM) to get more information about the penetration of the bleaching chemicals into the fibre surface. The hemicelluloses were determined by high performance liquid chromatography (HPLC) using a liquid chromatography mass spectrometer (LCMS) after hydrolysing polysaccharides to monosaccharides. In addition to this paper properties were analysed. This research confirms the effect of different hemicellulose compositions of the mechanical strength. The analyses represent the positive effect for paper production of the peracetic acid step in contrast to the ozone step. Additional the influence of the pulping process was determined by a sulphate pulp comparing with the sulphite pulp.