ALBERT

Description: Summary Delignification of spruce (Picea abies [L.] Karst.) during ASA (modified alkaline sulfite/anthraquinone pulping with alkali splitting) and magnesium bisulfite pulping was studied on a cellular level using scanning UV microspectrophotometry. This improved cellular analytical technique enables direct imaging of the topochemistry of lignin removal within the cell wall at different stages of cooking. The cooks were performed in a laboratory digester with forced liquor circulation. At 30 min intervals samples were taken for chemical and UV microscopic analyses. UV microscopy reveals that delignification during ASA pulping starts in the region of the pit canals and proceeds evenly across the entire S2 layer. As a specific feature of bisulfite pulping, a partial delignification of the radial compound middle lamella can be detected after 60 min of cooking. After 120 min, in both processes, the delignified cell walls show low UV absorbance values of both S2 and compound middle lamella. At this stage, approximately 90% of the initial lignin content is removed. At the end of both pulping processes, only parts of the cell corners can be distinguished by the new UV scanning technique.

Description: Summary The topochemical distribution of phenolic extractives in steamed and kiln-dried beechwood with discolourations was investigated on a cellular level by using scanning UV microspectrophotometry (UMSP). For the chemical characterisation of accessory compounds, acetone and methanol extracts of the discoloured beechwood were separated by accelerated solvent extraction (ASE) and analysed with high performance liquid chromatography (HPLC). The UV microscopic investigations reveal that the accessory compounds responsible for the discolouration of beechwood are mainly restricted to the longitudinal and ray parenchyma cells and the lumen of vessels. The detected extractives are characterised by high UV absorbance values and an absorbance maximum in a wavelength range between 280 and 290 nm. The separation of the acetone and methanol extracts of discoloured beechwood shows the presence of different low molecular phenols such as catechin and 2,6-dimethoxybenzochinon, which are transformed into high condensation compounds during steaming and kiln-drying.

Description: Summary In the present study, the biological, chemical and mechanical wood properties of “Wulstholz” as a response to mechanical stress of spruce trees (Picea abies [L.] Karst.) were investigated. “Wulstholz” is formed locally on the compression side of overstressed tree trunks after slip planes were initiated. It is characterized by an increased xylem production leading to bulges. The S2-layers of “Wulstholz”-tracheids are thicker than the corresponding cell wall layers in normal wood, and the cell lumen diameter is significantly reduced. The tracheid length decreases gradually from an average of 4 mm to 2.5 mm compared to normal wood, and the tracheids conspicuously are shifted against each other longitudinally. “Wulstholz” contains a higher concentration of lignin than normal wood, whereas the concentration of glucose in the hydrolysates is reduced. The hemicelluloses-concentration, particularly the mannose-content, is significantly higher compared to normal wood. The compression strength and the modulus of elasticity, despite a higher density, are significantly reduced in “Wulstholz” in comparison to normal wood. But due to the specific anatomical and chemical properties, “Wulstholz”-tracheids can be deformed and compressed considerably without fracturing. The investigations demonstrate that “Wulstholz” can restabilize wind-exposed trees.

Description: Summary The effect of two different wood modification treatments on the lignin of Norway spruce wood was studied by means of cellular UV-spectroscopy. The modification treatments chosen were acetylation using acetic anhydride and a two step hydrothermal treatment. Small cross sectional thin slides from the wood surface were taken and were subsequently analysed using a UV-micro-spectro-photometer. The modified samples were compared with a non-treated control sample. The results revealed changes in the absorption spectra of lignin after both modification treatments. Spectra of the compound middle lamella (CML) of acetylated wood revealed a decrease in the lignin-specific absorption maximum at 280nm, which is considered to be caused by superficial leaching of lignin due to acetylation. The retarding effect of acetylation on UV-degradation of wood is discussed. In hydrothermal-treated wood the 280nm maximum was increased within the S2 layer. This maximum remained almost unchanged in the CML while a lower maximum was observed at about 330nm. Changes in the chromophoric behaviour of lignin are probably caused by de-masking reactions within the S2 layer resulting from hydrolysis of carbohydrates and side chain reactions. Both treatments lead to a severe decrease in absorption at the lower end of the spectrum towards 250nm which is possibly attributed to changes or even splitting of biphenyls.

Description: Summary The localisation of lignin and phenolic extractives in woody tissue was determined using scanning UV microspectrophotometry. This improved cellular analytical technique enabled direct imaging of the topochemical lignin distribution within individual cell wall layers with a resolution of 0.25 μm2. Selected softwood (Picea abies), hardwood (Fagus sylvatica, Entandrophragma cylindricum, Prunus serotina) and monocotyledon (Phyllostachys edulis) sections of 1 μm thickness were scanned at a fixed wavelength and evaluated with the “APAMOS” software. This approach allowed the distribution pattern of lignins and aromatic extractives within the cell wall to be visualised simultaneously. The method was found to be ideally suited to the study of their subcellular distribution in plant cell walls.

Description: The present study investigated different log storage conditions and their influence on the processability of the wood material in pulping and bleaching. For that purpose, logs were stored for about 15 months under dry and wet conditions. Besides a detailed chemical, physical and microbial characterization of the wood, cooking trials according to the standard magnesium acid bisulfite process and bleaching experiments at various conditions using a (E/O)-Z-P-sequence were performed. The dependency of pulp yield, delignification efficiency, the course of cellulose depolymerization and brightness on the different storage conditions was evaluated. Bleaching selectivity was comparable for pulps made from fresh and wet-stored wood. In the case of pulp made from dry-stored wood, between 60% and 300% more bleaching chemicals, expressed as OXE, were necessary to obtain the target brightness. Milled wood lignin was isolated from the beech wood samples to study possible structural changes attributable to different storage conditions. Permanganate oxidation was applied to investigate the most important lignin structures. Additionally, preliminary NMR studies were performed to gain supplementary information about the composition of the lignin moieties. UV microspectrophotometry in agreement with absorption difference spectra strongly suggests that the chromophore structures present in both unbleached and bleached pulp samples predominantly originate from polyphenolic compounds, which are attached to the cell wall and are deposited in the lumina of parenchyma cells. From the results obtained so far, it can be concluded that wet storage of beech wood logs efficiently prevents the formation of chromophore compounds which negatively affect acid bisulfite pulping.