Volume 70, Issue 3

Hemicellulose O -acetyl-galactoglucomannan (GGM) is the main noncellulosic water-soluble polysaccharide in the coniferous softwood Norway spruce, consisting of anhydro-galactose, -glucose, and -mannose. Acid hydrolysis of GGM has been studied in a continuous tube reactor to obtain these sugars under industrially relevant conditions. The reaction was performed under atmospheric pressure at 90°C and 95°C, and hydrochloric acid (HCl) served as catalyst. The influence of the reaction parameters, such as acid concentration (pH), temperature, concentration of the substrate, as well as catalyst and reactant flow rates, has been studied on the conversion efficiency and product distribution. Continuous production of monomeric sugars was achieved without formation of low-molecular by-products. The GGM conversion was high with HCl as catalyst, at 95°C, and a pH of 0.3. The main hydrolysis products were mannose, glucose, and galactose monomers. Minor amounts of sugar dimers were detected among the products. The experimental results are described with a laminar flow model for the continuous reactor.

Activated carbon fibers (ACFs) have been prepared from liquefied wood (W liq ) by chemical activation with KOH, with a particular focus on the effect of KOH/fiber ratio in term of porous texture and surface chemistry. ACFs based on steam activation served as a blank for comparison. The properties of the ACFs were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption/desorption, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results show that the KOH-activated ACFs have rougher surfaces and more amorphous structure compared with the blank. The pore development was significant when the KOH/fiber ratio reached 3, and achieved a maximum Brunauer-Emmett-Teller (BET) surface area of 1371 m 2 g -1 and total pore volume (V tot ) of 0.777 cm 3 g -1 , of which 45.3% belong to mesopores with diameters of 2–4 nm, while the blank activated at the same temperature had a BET surface of 1250 m 2 g -1 and V tot of 0.644 cm 3 g -1 , which are mainly micropores. The surface functional groups are closely associated with the KOH/fiber ratios. KOH-activated ACFs with KOH/fiber ratio of 3 have more oxygenated surface functional groups (C-O, C=O, -COOH) than the blank.

The water vapour sorption data of untreated (W untr ), acetylated (W ac ) and formaldehyde-treated (W FA ) Scots pine ( Pinus sylvestris L.) sapwood were analysed in terms of their sorption kinetics and were transformed into excess surface work (ESW) isotherms. The sorption kinetics were studied by fitting the non-linear parallel exponential kinetics (PEK) model to the experimental data in which the sorption kinetics curve is composed of two processes (fast and slow components). W ac and W FA showed evident differences in their sorption kinetics and their thermodynamic sorption behaviour. In contrast to acetylation, formalisation influenced both the extent of the slow sorption process and the shape of its pseudoisotherm. For W untr and W ac , it appears that some water associated with the slow process is adsorbed at sites for fast sorption newly generated upon swelling (previously postulated as extra water) and subsequently desorbed by the fast process. For W FA , the formation of extra water hardly occurs. ESW was reduced through acetylation with a constant factor over the whole hydroscopic range, whereas the ESW of W FA was reduced only after reaching the monolayer capacity compared to its control. The sorption behaviour of W ac was solely determined by cell wall bulking, whereas that of W FA was governed by the increased matrix stiffness due to cross-linking of the cell wall polymers.

Thermal modification (TM) of wood has occupied a relatively narrow but stable niche as an alternative for chemical wood protection. There are different technological solutions for TM and not all details of their effects on wood tissue have been understood. The one-stage hydrothermal modification (HTM) at elevated vapour pressure essentially changes the wood’s composition and structure. In the present paper, the changes in three hardwood lignins (alder, aspen, and birch) were observed within the cell wall by means of cellular UV microspectrophotometry. The lignin absorbances in the compound middle lamella (CML) of unmodified wood are 1.7- to 2.0-fold higher than those in the fibre S2 layer. The woods were modified in the temperature range from 140 to 180°C, while in the lower temperature range (140°C/1 h), the UV absorbances are little affected. Essential changes occur in the range of 160–180°C and the UV data reflect these by absorbtion changes, while the absorbances at 278 nm rise with factors around 2 more in the S2 layer than in the CML. The absorbance increments are interpreted as polycondensation reactions with furfural and other degradation products of hemicelluloses with the lignin moiety of the cell wall.

A dynamic interrelationship exists among wood density and fiber traits (tracheid length and microfibril angel, MFA) and the ultimate wood strength properties. Moreover, many of the basic fundamental wood attributes are heavily influenced by crown size and architecture. In an attempt to examine this interplay, we thoroughly characterized 60 interior spruce ( Picea glauca × P. engelmannii ) trees sampled in three age classes from four sites in central British Columbia. Breast height discs were taken, and relative wood density was measured along two radii. Tracheid length was assessed on isolated 5 years increments from pith to bark at breast height for each tree, as was MFA. Segmented regression was used to identify the “juvenile to mature wood” transition point, which revealed transition ages of 9.4 and 15.1 years for wood density and MFA, respectively, while fiber length continued to elongate until near 60 years of age. The flexural properties, modulus of elasticity (MoE) and modulus of rupture (MoR), were also quantified in the 60 individuals and found to be best predicted by V FV , a measure of tree vigor, and not the basic wood attributes. These findings imply that long crowns carrying large amounts of foliage, V FV , negatively impact wood strength in interior spruce.

A 3D numerical solution of the heat conduction equation is proposed based on the finite volume method to describe the heating of wood, where the thermal conductivity (ThC) is variable, and the convective heat transfer coefficient is constant. ThC parameters were found through an optimization process based on genetic algorithms. The objective function between measured and simulated curves is determined, and parameters with greatest correspondence between measured and estimated values were obtained. As a result, a new equation for ThC is proposed, which depends on moisture and temperature. The proposed coefficient is validated by experiments, and a good agreement was found between experimental heating curves and those obtained by simulation by means of the new heat conduction equation.

Pre-extraction of hemicelluloses from lignocellulosic feedstock has been a research focus during the last decade within the context of lignocellulosic biorefineries. In this study, the effect of hot-water extraction (HWE) on the topochemistry and ultrastructure of poplar wood ( Populus sp. ) was investigated based on scanning electron microscopy (SEM) and transmission electron microscopy (TEM) paired with immunogold labeling of the hemicelluloses. The cell walls of HWE wood (HWEW) differ significantly in their ultrastructure from neat wood, i.e., there are many distorted cells and agglomerations of lignin and extractives agglomerations in the cell lumina. Results of immunogold labeling indicate that different types of hemicelluloses are extracted at different stages and both their concentration and distribution within the wood cell wall layers are affected by the HWE. Hemicelluloses more closely associated with lignin appear to be more easily removed by HWE. Lignins are also extracted partially and altered. Results provide a holistic view of chemical and ultrastructural changes including the associated changes in hemicelluloses and lignin distribution in HWEW. The obtained data could be helpful to understand better the mechanical properties and adhesion related issues of HWEW for wood composite production.

The mode of action of phenol-formaldehyde (PF)-modified wood has been investigated with respect to its resistance to brown rot decay. The Fenton reaction is assumed to play a key role in the initial brown rot decay. Pine microveneers were modified to various weight percent gains (WPG) with low molecular weight PF and exposed to a solution containing Fenton’s reagent. The mass loss (ML) and tensile strength loss (TSL) as well as the decomposition of hydrogen peroxide within the incubation time decreased with the increasing WPG of the veneers. Incubation of untreated and PF-modified veneers in acetate buffer containing ferric ions without H 2 O 2 revealed that the modification strongly reduces the uptake of iron by the wood cell wall. Further studies indicated that lignin promotes the decay of wood by Fenton’s reagent. The reason for the enhanced resistance of modified wood to the Fenton reaction is attributable to the impeded diffusion of iron ions into the cell wall rather than to the blocking of free phenolic sites of lignin, which accelerate redox cycling of iron.

Stilbenes are abundant in the heartwood of Scots pine ( Pinus sylvestris L.) and are known to have strong antifungal efficiency. In this study, Scots pine sapwood blocks were impregnated with crude heartwood extract containing the stilbenes pinosylvin (PS) and the pinosylvin monomethyl ether (PSM). Impregnated blocks were submitted to brown-rot fungi, Coniophora puteana , Gloeophyllum trabeum, and Rhodonia (Poria) placenta , and fungal growth test and decay test were performed. Both tests showed that the impregnation with a high concentration of stilbenes (60 mg g -1 dry wood) significantly suppressed the growth of fungi and slowed down the decay process of wood blocks, especially in case of G. trabeum . However, chemical analysis showed that PS and PSM were degraded by all the three types of fungi, obviously via modification to resveratrol and methylresveratrol. Rhodonia placenta displayed the fastest rate of degradation. Thus, impregnation with biodegradable stilbenes could be a viable alternative for wood preservation only in service situations with low or transient risk of decay.

Ginkgo ( Ginkgo biloba L.) forms thick, lignified secondary xylem in the cylindrical stem as in Pinales (commonly called conifers), although it has more phylogenetic affinity to Cycadales than to conifers. Ginkgo forms compression wood-like (CW-like) reaction wood (RW) in its inclined stem as it is the case in conifers. However, the distribution of growth stress is not yet investigated in the RW of ginkgo, and thus this tissue resulting from negative gravitropism is still waiting for closer consideration. The present study intended to fill this gap. It has been demonstrated that, indeed, ginkgo forms RW tissue on the lower side of the inclined stem, where the compressive growth stress (CGS) was generated. In the RW, the micorofibril angle in the S2 layer, the air-dried density, and the lignin content increased, whereas the cellulose content decreased. These data are quite similar to those of conifer CWs. The multiple linear regression analysis revealed that the CGS is significantly correlated by the changes in the aforementioned parameters. It can be safely concluded that the negative gravitropism of ginkgo is very similar to that of conifers.