Volume 75, Issue 1

Xylan deposition and lignification processes were examined in tension wood fibers with gelatinous layers (G-layers) in Mallotus japonicus (Euphorbiaceae). The cell walls consisted of a multi-layered structure of S 1  + S 2  + G +  n (L + G), where n indicates the number of repetitions ( n  = 0–3) and L indicates very thin lignified layers. The formation and lignification processes of the multi-layered structure of tension wood fibers were examined by light microscopy, ultraviolet microscopy, and transmission electron microscopy (TEM) following KMnO 4 staining. The deposition of xylan was examined by immunoelectron microscopy with a monoclonal antibody (LM11). Immunolabelling of xylan appeared in lignified cell wall layers, except in the compound middle lamella (CML), i.e., the S 1 , S 2 , and L layers but not the G-layers. The density of LM11 xylan immunogold labeling in S 2 layers increased during the formation of G-layers. This increase was due to the shrinkage of S 2 layers during development rather than intrusive deposition of xylan through G-layers. Lignification of the CML, S 1 , and S 2 layers proceeded during G-layer formation. The shrinkage of S 2 layers occurred almost simultaneously with the lignification of the S 2 layers during G-layer formation, suggesting that the S 2 layers shrank with lignification.

Whether water sorption hysteresis exists above 75 °C and the representation of its relationship with wood softening remains unclear. In this study, sorption hysteresis at three temperature levels, namely, 75, 90 and 99.5 °C, was investigated using accurately controlled conditioning chambers using powder samples from seven wood species. The dry mass loss percentage of the samples and proper equilibrium time was evaluated by pretests to ensure reliable sorption isotherms afterwards. The dry mass loss percentage after the entire sorption isotherm running needs to be kept within 0.5% to avoid complications in determining the equilibrium time. The abrupt increase of equilibrium moisture content at high relative humidity regions and the crossover of adsorption isotherms were not observed. Hysteresis was conspicuous at 75 and 90 °C and was statistically confirmed at 99.5 °C. High sample extractives content or unnecessarily long equilibrium time would cause significant sample dry mass loss, which may suppress the desorption isotherm to an extent that leads to unjustified hysteresis disappearance. The hysteresis behavior observed in this study suggests that wood softening does not necessarily result in hysteresis disappearance, and the explanation of hysteresis progression as a function of wood softening temperature must be evaluated with care in the future.

Forests are under great pressure due to climate changes. It is forecast that the importance of Mediterranean type forests will significantly increase. Among various types of oak species, pubescent oak ( Quercus pubescens ) will likely gain ecological and economic importance in the region south of Alps. Although this wood species is well known, there are not much data available about chemical properties and durability. A comprehensive analysis of extractives and durability against wood decay fungi was therefore performed. The results of the chemical analysis revealed that heartwood contains up to 20% of the extractives, with considerable amounts of phenols, including a fairly high concentration of Gallic acid (GAc). Anatomical structure, with high frequency of tylosis, resulted in good water exclusion efficacy. The presence of biologically active extractives and superior water exclusion efficacy resulted in good durability, as shown by basidiomycetes tests. Based on the laboratory data, factors that determine the service life of wood were calculated. Data indicate superior performance in above-ground applications.

Modification of wood improves certain properties of natural wood and presents competitive alternatives to synthetic materials that may have larger environmental impacts. One aspect of modified wood that is currently not fully understood is the dynamic performance and how it is affected by the modification process. In this study, low-molecular weight phenol formaldehyde (PF) resin was applied to Scots pine ( Pinus sylvestris L.) and European beech ( Fagus sylvatica L.) wood. The effect of this modification was evaluated using a three-point bending test undergoing cyclic loading. Compared to reference samples, modified wood showed higher static performance but revealed a reduction in cyclic fatigue strength (9% for pine and 14% for beech). Cyclic fatigue strength of unmodified wood was found to be 67% of the static modulus of rupture for both species. With PF resin modification, the fatigue strength dropped to 58% for pine and 53% for beech. While fatigue strength decreased, there was no reduction in cyclic modulus or change in the creep rate within the stationary creep phase. It is important to consider the reduction in fatigue strength when using PF modified wood for any construction purposes with expected cyclic loading conditions.

The aim of this study was to evaluate the characteristics of radio-frequency/vacuum combined with mechanical press (RF/VP) drying on three softwood timbers (Douglas fir, Hemlock, and Radiata pine) with longitudinal kerfs. The results were as follows: Due to the dielectric permittivity of wood, RF/VP drying at a fixed frequency of 13.56 MHz significantly influenced the moisture content (MC) distribution, the number of surface checks, shrinkage, and warp. These observations were attributed to the formation of a temperature gradient along the charge plate during the drying. The presence or absence of pith, more affected an occurrence of surface checks than that of the stresses within the wood during drying. The longitudinal kerf reduced the number of surface checks, but did not affect the MC distribution or the twist after drying.

Natural constituents of wood cell-wall layers are affected in various ways by thermal treatment. This study investigated the effect of high-temperature treatment on the properties of cell-wall layers. The properties were studied using PeakForce quantitative nanomechanical mapping and Fourier-transform infrared spectroscopy (FTIR). European beech wood was thermally treated at 200 °C for 1, 3, and 5 h in an oxidizing atmosphere. Modulus of elasticity, adhesion force, and roughness of the secondary S 2 layer and the compound middle lamella (CML) were determined using atomic force microscopy (AFM). Results showed that both the S 2 layer and CML were affected by thermal treatment. Stiffening of the S 2 layer was caused by increased crystallinity of the cellulose-dominated component, having peaked after 1 h of treatment. The degradation thereafter resulted in a decrease of the S 2 as well as the CML stiffness. An increase of CML roughness after 3 h of treatment was associated with the effect of thermal degradation on CML integrity. The analysis suggested that the reduction in syringyl lignin is potentially associated with an increase in adhesion of cell-wall layers.

This study presents a novel application of the Wilhelmy plate method on welded joints of Scots pine sapwood and beech. Welding resulted in an increase in the contact angle (increased hydrophobicity) as well as a decrease in the water uptake and swelling of the welded pine-joint compared to non-welded pine. When the welding time was extended from 4 to 5 s, these properties were further pronounced. Welding of beech, on the other hand, led to an increase in the contact angle and a decrease in the water uptake, but an increase in the swelling. Fourier Transform Infrared spectroscopy showed that welding increased the aliphatic C–H and unsaturated C=C stretching absorption bands in pine and beech. Scanning electron microscopy showed a dense structure at the welded joints of the both species, giving evidence of a lower porosity that leads to a lower permeability as a result of the welding.

The effect of wollastonite on the wetting properties of welded Scots pine-joints was studied using the multicycle Wilhelmy plate method and by observation of the chemical composition of the welded joints. Welding pine with wollastonite for 5 s resulted in a decrease in the water uptake and the swelling, and an increase in the contact angle of the welded joint compared to welded wood without wollastonite. High-performance liquid chromatography and gas chromatography/mass spectrometry showed the presence of dehydration products such as furfural, 5-hydroxymethylfurfural, and levoglucosan in methanol extracts from welded joints of specimens welded with and without wollastonite. Phenols were also found by analysis using the Folin-Ciocalteu method and High-performance liquid chromatography. The importance of such compounds in relation to the wetting properties of the welded joint is discussed.

The broad applicability of the wood modification protocol recently published by Kaufmann et al. allows to improve the fire resistance of renewable materials, too. In this study organophosphorus and organoboron compounds have been synthesized, characterized and subsequently applied for enhanced flame retardancy of wood. Wood hydroxyl groups of Scots pine ( Pinus sylvestris L.) sapwood veneer chips were covalently modified upon esterification with benzotriazolyl-activated P- and B-substituted benz-amides. The efficacy of this synthetic strategy was demonstrated by the weight percent gain (WPG) of up to 32% and the corresponding quantities of covalently bonded organicmaterial (QCO) of up to 1.1 mmol/g, respectively. The successful covalent attachment of the functional precursors was proven by attenuated total reflection infrared spectroscopy (ATR-IR). The effect of the flame retardants on the properties of the modified sapwood samples was shown by a significant decrease of the temperature of mass loss from about 346–248 °C in the thermogravimetric analysis (TGA).

In this study, oriented bamboo scrimber board (OBSB) was manufactured with a synthesized formaldehyde-free tannin adhesive. The chemical properties of the tannin adhesive were analyzed with 13 C nuclear magnetic resonance spectroscopy ( 13 C-NMR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). Results revealed that 70% aqueous acetone extractives of Acacia confusa bark (AcBAE) contained abundant phenolic compounds and condensed tannins comprising mainly B-type flavonoid bonds. Moreover, cross polarization magic angle spinning (CP/MAS) 13 C-NMR mapping of cured Acacia confusa bark tannin glue (AcBTanGlu) revealed that condensed tannin reacted with hexamethylenetetramine to form a polymer with a cross-link structure through a polymerization mechanism. According to the results obtained from gas chromatography-flame ionization detector (GC-FID) analysis, no formaldehyde was emitted from AcBTanGlu-glued OBSB. Thermogravimetric analysis indicated that AcBTanGlu significantly improved the thermal stability of AcBAE after the curing reaction. Comparison of the DRIFT spectra of bamboos before and after AcBTanGlu-glued treatment indicated AcBTanGlu did not impact the chemical functional properties of the bamboo. Compared to phenol formaldehyde (PF) and urea formaldehyde (UF)-glued OBSBs, AcBTanGlu-glued OBSBs statistically had lower modulus of elasticity (MOE) and modulus of rupture (MOR). As for the nail withdraw resistance, AcBTanGlu-glued OBSBs are statistically comparable to PF-glued OBSBs and higher than UF-glued OBSBs.