Volume 72, Issue 1

A quantitative method has been developed for assessment of the distribution of xylan across the secondary cell wall layers of Eucalyptus dissolving pulp fibres by means of a carbohydrate binding module (CBM), Ct CBM6, in combination with transmission electron microscopy (TEM). To ensure reproducibility and to minimise non-specific labelling, various parameters were optimised, namely the size of the gold colloid marker, Ct CBM6 concentration, and the selection of buffer solutions. The method was replicated on processed Eucalyptus fibres containing different xylan contents. Reproducible xylan counts and distributions across the secondary cell wall layers were obtained for unbleached and bleached Eucalyptus fibres. The xylan distribution pattern across the cell wall layers S1, S2 and S3 was similar, but the S1 and S3 layers contained after bleaching more xylan than the S2 layer. The technique has a wide range of applications in basic wood research as well as in the analysis of technological processes.

Diarylheptanoids are a group of secondary metabolites widely distributed in the Betulaceae family and characteristic for Alnus species. In this study, the chemotaxonomic power of diarylheptanoids, such as hirsutanonol-5- O - β - d -glucopyranoside, rubranoside A, oregonin, platyphylloside, alnuside A and hirsutanonol, has been investigated in combination with principal component analysis (PCA) for differentiation of Alnus species. Concentrations of six diarylheptanoids in the bark extracts of two natural populations of Alnus glutinosa (black alder) and Alnus incana (gray alder) were determined by ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). PCA clearly shows the separation of three groups. Populations I ( A. glutinosa ) and II ( A. incana ) both consisted of individuals of the corresponding species. Four individuals from both sampled populations formed a separate group (population III), which possibly represents a hybrid group. Accordingly, diarylheptanoids may serve in combination with PCA as chemotaxonomic markers at the species level, which may also reveal hybrid species.

Acetylated wood (W Ac ) shows improved properties largely due to the reduced amount of water in its cell wall, but the exact mechanism of water reduction remains unclear. Acetylation reduces hydroxyl (OH) content by acetyl (Ac) substitution but may also limit water access to unmodified OH groups by steric hindrance. In the present work, the accessibility of OH groups in acetylated or propionylated Radiata pine ( Pinus radiata D. Don) wood (W Ac and W Pr ) was investigated by deuterium exchange, saponification in sodium hydroxide followed by high-performance liquid chromatography (HPLC) analysis and weight percentage gain determination of the modified samples. Acetylation reduced OH accessibility (OH A ) to a greater extent than would be predicted, if OH substitution were the only responsible mechanism for accessibility reduction. The combination of deuterium exchange and saponification results provides strong evidence that steric hindrance plays a key role in reduction of water accessibility to unmodified OH groups in W Ac . The supramolecular architecture of W Pr samples seems to be modified by the propionylation reaction, which leads to increased OH A at low levels of substitution. This suggests that molecular restructuring within the cell wall exposes new OH groups after propionylation. At higher levels of substitution, however, the W Pr exhibited less OH A than expected indicating steric hindrance from the propionyl groups.

The outer bark of Douglas-fir ( Pseudotsuga menziesii ) has a significant amount of cork tissue that may be an important source of chemicals derived from its natural polymers, suberin, cellulose, hemicelluloses and lignin. The present work focuses on the polyalcohol liquefaction of Douglas-fir bark with glycerol and polyethylene glycol (PEG) in order to obtain a liquid that can be further processed to other chemicals and products. The results show that Pseudotsuga bark can be liquefied in a significant percentage in presence of alkali. The best liquefaction yield was obtained with 6% KOH as agents. Although the use of a cosolvent is favorable, good liquefaction yields can also be obtained by glycerol alone. Lower temperatures are favorable as they lead to acceptable liquefaction yields. FTIR-ATR studies showed that all the structural compounds of the bark were attacked and depolymerized. The process tested has a high potential for generation of value-added products from liquefied Douglas-fir bark.

Transverse sections of white birch ( Betula platyphylla ) were treated with anhydrous ammonia at 60–140°C (ammonia treatment, AT). As a result, the crystal structure of cellulose in the AT samples changed to cellulose III I , and acetamide was produced. The surface area of the AT samples, the amount of sugar released upon acid hydrolysis and the lignin content were not changed. However, a small amount of lignin became acid soluble. Mäule color reaction, indicative of the presence of syringyl lignin, showed decreasing color intensities with increasing temperature of AT. The results can be easily interpreted that AT affects ester linkages and side chains of hemicelluloses and syringyl lignin. In addition, AT was carried out on 1-μm thick transverse sections and block specimens. Xylanase treatment and immunolabeling revealed that AT enhances xylan degradation, but ray cells are resistant to xylanase even after AT. On the block sample, a deposited xylan layer appeared on the inner surface of fiber cell walls. Apparently, xylan moved to the surface in contact with the fluid ammonia during AT. The vessel cell wall did not show a similar migration effect, indicating a cell wall-specific interaction with ammonia.

The modification of heat-treated wood (HTW) wettability by cold atmospheric-pressure nitrogen plasma jet (APPJ) for several treatment durations has been investigated. The effects of the modification were assessed by measurement of the advancing contact angle (ACA) of water along with determination of surface free energy. Additionally, the morphology and chemical changes of the HTW surface were characterized by scanning electron microscope (SEM) and FTIR spectroscopy. As expected, the measurements demonstrated that the ACA decreased proportionally with treatment time of APPJ. The optimal treatment time was 20 s. Clear etching traces are visible on the SEM images of HTW surfaces. The roughness of HTW increased after plasma treatment. FTIR spectra demonstrate that OH, C=O, and COOH groups are formed on the HTW surfaces. All these modifications are beneficial for the HTW wettability, which leads to better bonding strength of HTW.

The present research deals with a simple dipping method to insert octadecyltrichlorosilane (OTS) into cell walls of spruce wood and to deposit OTS layers on its inner and outer surfaces. Distribution and chemical interactions of OTS with wood polymers has been investigated by scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The OTS/n-hexane solution penetrated into wood via capillary forces through ray tracheids and bordered pits and was deposited as OTS organic-inorganic layers on wood cell walls. The hypothesis is supported by the results, according to which the OTS molecules are hydrolysed by the wood moisture and by free OH groups of the cell wall components. The hydrolysed OTS molecules react with the OH groups and elevate the hydrophobicity of wood.

In focus of the present study was the mercury intrusion porosimetry (MIP) of heartwood (hW) and sapwood (sW) of Scots pine, which were modified by compression alone (C) and combination of C and heat treatment (CHT). The untreated sW has a more uniform pore distribution than that of hW as presented in logarithmic differential curves. Expectedly, the total pore volumes of CHThW and CHTsW are significantly decreased. Compared to the HT temperature (180–220°C), the exposure time (2–5 h) has a weaker effect on the pore structures of the CHT woods. Furthermore, the intrusion volume of CHThW decreased compared with compressed alone samples. However, an inverse result was apparent for CHTsW.

Lightweight construction of composites is one of the strategies for developing material-saving panels, whereas light honeycomb boards or sandwich panels (SPs) based on foam or wood materials seem to be very promising in this context. The objective of the present work was the development of an SP with a reduced density based on nearly 100% expanded maize granular in the core layer, which was combined with 3 mm thin and stiff poplar plywood as face materials. In focus were mechanical and physical properties of the SPs, which should be applicable in the furniture industry and competitive with conventional wood composites such as fibreboards or particle boards.

The mechanical properties of walnut ( Juglans regia L.) and cherry ( Prunus avium L.) woods, as frequent raw materials in cultural heritage objects, have been investigated as a function of the anatomical directions and the moisture content (MC). The strength data are decreasing with increasing MC, whereas the tensile strength in the longitudinal direction is higher by factors of 1.5–2 compared to the compression strength. Moreover, the inequality of tensile and compressive stiffness is discussed, which is a matter of debate since a long time. This so-called bimodular behavior is difficult to describe in a generalized mode due to the high data variability if tension and compression properties are analyzed on different samples. If tensile and compressive stiffness tests are performed on the same samples of walnut and cherry wood, the ratio between these properties is significantly higher than 1.