Volume 70, Issue 9

A large amount of monolignol glucosides (MLGs: p -glucocoumaryl alcohol, coniferin, syringin) are found in lignifying soft xylem near cambium and they disappear with the progress of lignification. Recently, it became a matter of debate whether those MLGs are real intermediates in lignin biosynthesis or only a storage form of monolignols outside of the main biosynthetic pathway. The latter is partly based on a misinterpretation of 14 C-tracer experiments and partly on the simple generalization of the results of gene manipulation experiments concerning the flexible and complex lignification. In the present paper, it could be confirmed by the most reliable 13 C-tracer method that MLGs are real intermediates in the pathway from l-phenylalanine to macromolecular lignin-polysaccharides complexes in the cell walls. This pathway via MLGs is essential for transport and programmed delivery of specific monolignols in a stable form from intracellular space to specific lignifying sites within the cell wall. The pool size of MLGs is large in most gymnosperm trees and some angiosperm species that emerged in an early stage of phylogeny, while the pool size is small in most angiosperms. This difference in pool size is reasonably understandable from the viewpoint of plant evolution, in the course of which the role of MLGs changed to meet variation in type of major cells, reaction wood formation, and postmortem lignification.

The degradation kinetics of a non-phenolic lignin model compound with α-carbonyl functionality (adlerone) has been studied by varying temperature and concentrations of sodium hydroxide, sodium hydrogen sulfide, and sodium sulfite. The kinetics of adlerone degradation and formation of its reaction products were monitored by UV-Vis spectroscopy and their structures were analyzed by GC/MS. The two step degradation of adlerone was studied in two separate experimental setups. In the first alkali catalyzed step, adlerone is converted to a β-elimination product that reacts further in the second step with hydrogen sulfide or sulfite ion. The Arrhenius kinetic parameters were derived by the KinFit software. The activation energy for the 1 st step was 69.1 kJ mol -1 , and for the 2 nd step with sulfide 42.4 kJ mol -1 and with sulfite ion 35.8 kJ mol -1 . The reaction mechanisms presented are in line with those published earlier: β-ether bonds of structures having α-carbonyl functionality do not cleave under soda pulping conditions, whereas in kraft and sulfite pulping the cleavage of β-ether bonds proceeds via nucleophile attack and addition. The combination of hydroxyl and sulfite ions gives the fastest cleavage of β-ether bonds in non-phenolic lignin structures with the α-carbonyl functionality.

Eucalyptus urophylla hybrids are important raw materials for the forest industry in Brazil, and large quantities of barks are available at mill site that may be used for added-value products. The chemical composition of barks of six commercial hybrids clones of E. urophylla × E. grandis , E. urophylla × E. Camaldulensis , and undisclosed E. urophylla hybrids was studied. The hybrids had similar composition, on average (data based on oven dry bark): 16% extractives, mainly corresponding to polar compounds that are soluble in ethanol and water, 19% lignin, 47% polysaccharides, 1% suberin, and 2% ash. The polysaccharides consists mainly of cellulose as indicated by 84% of total neutral monosaccharides in the acid hydrolysate and 10% xylose. The compositions of the lipophilic extracts was determined by GC-MS before and after alkaline hydrolysis. In all the barks, fatty acids, and triterpenes (namely: betulinic and ursolic acids) were the most abundant compounds followed by smaller amounts of sterols, long-chain aliphatic alcohols, phenolic acids, and acylglycerols. The ethanol-water bark extract had a high phenolic content: total phenolics ranged 211–551 mg gallic acid equivalents (GAE) g -1 of extract, tannins 76–184 mg catechin equivalents (CE) g -1 extract, and flavonoids 98–234 mg CE g -1 of extract. The antioxidant activity corresponds to 338 mg Trolox g -1 of extract. Development of high-value products is proposed through an integrated biorefinery approach including valorisation of extractives and targeting for cellulose-based applications.

Fiber (tracheid) length is an important trait targeted for genetic and silvicultural improvement. Such studies require large-scale non-destructive sampling, and accurate length determination. The standard procedure for non-destructive sampling is to collect increment cores, singularize their cells by maceration, measure them with optical analyzer and apply various corrections to suppress influence of non-fiber particles and cut fibers, as fibers are cut by the corer. The recently developed expectation-maximization method (EM) not only addresses the problem of non-fibers and cut fibers, but also corrects for the sampling bias. Here, the performance of the EM method has been evaluated by comparing it with length-weighing and squared length-weighing, both implemented in fiber analyzers, and with microscopy data for intact fibers, corrected for sampling bias, as the reference. This was done for 12-mm increment cores from 16 Norway spruce ( Picea abies (L.) Karst) trees on fibers from rings 8–11 (counted from pith), representing juvenile wood of interest in breeding programs. The EM-estimates provided mean-fiber-lengths with bias of only +2.7% and low scatter. Length-weighing and length 2 -weighing gave biases of -7.3% and +9.3%, respectively, and larger scatter. The suggested EM approach constitutes a more accurate non-destructive method for fiber length (FL) determination, expected to be applicable also to other conifers.

The identification of wood species in paper products is highly important for the enforcement of the newly established timber regulations regarding the control of illegal logging. In the context of European Timber Regulation (EUTR), in the present paper a database has been established containing reference samples and anatomical descriptions for the identification of 23 tropical timbers from Southeast Asia in pulp and paper products. The vessel elements and fibers of these mixed tropical hardwoods (MTH) were characterized by light microscopy. The woods in focus were macerated, embedded and compared visually and statistically. The collected microscopic data and images are helpful for the identification of the wood species used for paper production.

A more accurate prediction of the mechanical behavior of wood is needed to increase its ability to compete with other building materials. Especially, when it comes to estimate failure loads, the lack of appropriate prediction tools becomes obvious. The present work contributes to this goal in two different ways: First, a damage concept for wood is revisited, which allows for transferring information about failure processes through different scales of observation. In this concept, the failure behavior of clear wood is linked to the different characteristic of earlywood and latewood layers in softwoods. This reduces the number of empirically determined strength parameters, while the definition of multisurface failure criteria is still possible. Secondly, it will be demonstrated that the combination of these models with discrete crack modeling based on the extended finite element method provides a numerical simulation tool capable to describe failure mechanisms more realistically than existing approaches. The results obtained by numerical calculations and experiments by means of a micro wedge splitting test show very good agreement, especially, if the load capacity and failure mechanisms are in focus. The presented approach shows a much better performance compared to linear elastic or elastoplastic simulations.

Oak from the Swedish warship Vasa and recent oak that was aged after impregnation with iron(II) chloride has been analyzed by FT-IR spectroscopy and submitted to tensile strength testing. The aim was to investigate correlations between FT-IR bands in the fingerprint region, chemical degradation, and tensile strength in iron contaminated oak. The concentration of carboxylic functions increased and the acetyl groups in the hemicellulose fraction were decreasing as a function of degradation time. These changes are accompanied by reduced tensile strength and elevated content of oxalic acid (OA) in both Vasa wood and the impregnated recent oak samples. To evaluate the possibility to predict tensile strength from spectral data, chemometric modeling by partial least-squares (PLS) regression was applied. The strategy of repeated double cross validation (rdCV) allowed a realistic prediction of tensile strength. Overall, chemical changes and mechanical performances of iron contaminated wood are strongly correlated and thus FT-IR spectroscopy is suited to predict the strength properties of the degraded wood.

Wood can be considered as a highly porous, three-dimensional organic scaffold. It can be mineralized to create hierarchically structured organic-inorganic hybrid materials with novel properties. In the present paper, the precipitation of CaCO 3 mineral in Norway spruce and European beech wood has been studied by alternating impregnation with aqueous and alcoholic electrolyte solutions. Microstructural imaging by SEM and confocal Raman microscopy shows the distribution of calcite and vaterite as two CaCO 3 polymorphs, which are deposited deep inside the cellular structure of the wood. The confined microenvironment of the wood cell wall seems to favor a formation of vaterite, as visible by XRD and Raman spectroscopy. In view of a practical application, the mineralization of wood opens up ways for sustainable wood-based hybrid materials with a significantly improved fire resistance, as proven via pyrolysis combustion flow calorimetry and cone calorimetry tests. Beyond that, this versatile solute-exchange approach provides an opportunity for the incorporation of a broad range of different mineral phases into wood for novel material property combinations.

Softwoods (SW, spruce and fir) and hardwoods (HW, ash and beech) were thermally modified by the thermo-vacuum (Termovuoto) process for 3–4 h in the temperature range 160–220°C (TMW 160–220°C ) and their fungal durability were examined in soil-block tests with two brown rot (BR, Postia placenta, Gloeophyllum trabeum ) and two white rot (WR, Pycnoporus sanguineus, Phlebia radiata ) fungi. SW-TMW 160–220°C were exposed to P. placenta and P. sanguineus and HW-TMW 190–220°C to all fungal species. Considerable improvement (durability class 1–3) in decay resistance was only achieved for SW- and HW-TMW 220°C . Thermal modification (TM) below 200°C influenced decay resistance negatively in case of some fungal species applied for both SW and HW. Judged by the durability class, decay resistance was higher in HW- than in SW-TMW at high TM temperature. Behavior of TM differed significantly between ash (ring-porous HW) and beech (diffuse-porous HW). A comparison between results of soil- and agar-block tests on Termovouoto wood demonstrated that the influence of testing method in terms of assignment to durability classes is not significant.

Equilibrium moisture content (EMC), mechanical properties, and durability of Scots pine ( Pinus sylvestris L.) sapwood modified by vinyl acetate epoxidized linseed oil (W VA-ELO ) have been studied. Microscopic observations revealed that the impregnated copolymer is mainly in cell walls, rays, resin canals, and a small fraction in the cell lumens. Under the same climate conditioning, the EMC of the treated wood was in the range of 6.0%–8.2%, which was significantly lower than that of untreated wood (about 12%). Mechanical tests performed on paired samples (control and treated) showed a slight reduction on the mechanical properties of W VA-ELO . The decay resistance against basidiomycete fungi of W VA-ELO was significantly improved as demonstrated by laboratory tests. It was found that 8% weight percentage gain (WPG) was sufficient to ensure decay resistance against the test fungi with <5% mass loss (ML), which led to durability class (DC) of 2.

Aldehydes and terpenes are the most frequently emitted volatile organic compounds (VOCs) in the wood-processing industry. These emissions are classified as injurious to health and hazardous to the environment. To address this problem, the growth conditions have been identified under which bacteria extensively degrade both aldehydes and particularly terpenes in pine wood particles as a raw material for the production of particle boards. In this study, the focus was on pentanal and hexanal (aldehydes) as well as α- and β-pinene (terpenes). Bacterial strains were selected for their ability to metabolize α-pinene as single carbon source in liquid culture medium. α-Pinene degradation was then determined by gas chromatography (GC) analysis. Strains belonging to the genus Pseudomonas showed the best results (98% degradation after 72 h). Comparably good results were also achieved with the thermophilic strain Bacillus pallidus (90% degradation) at 55°C. Furthermore, an adapted mixed culture of Pseudomonas species was inoculated onto wood particles and incubated at room temperature for 3 days. Solid-phase microextraction (SPME) measurements of emitted volatiles and subsequent gas chromatography-mass spectrometry (GC-MS) analysis indicated a complete removal (100%) of aldehydes and, even more importantly, α- and β-pinene. Pre-treatment of unsterile pine wood particles with Pseudomonas species may have potential for industrial application.