Volume 69, Issue 4

A large-scale test set-up was designed to evaluate the volatile organic compound (VOC) emissions of building materials in a real room situation but under laboratory conditions. Two model rooms (ModR) with a volume of 30 m 3 each were constructed of the wood-based building materials X-lam and OSB, respectively. Temperature and relative humidity (RH) inside the ModR were kept in a range of 21°C–25°C and 45%–55% RH. VOCs were collected at 13 different times over a period of 23 weeks, and the total VOC (TVOC) concentration was calculated from GC/MS data. Results were quantified as toluene equivalents (TE). In the X-lam-ModR, the TVOC concentration decreased by 64% over the whole measurement period from 115 to 41 μg m -3 TE. Terpenes were the most abundant substance group and accounted, on average, for 80% of the TVOC concentration. In the OSB-ModR, the TVOC concentration decreased by 72% from 443 to 124 μg m -3 TE. Aldehydes showed the highest concentrations, accounting, on average, for 52% of the TVOC, while 38% were terpenes. The results show that this type of test provides realistic data for the praxis.

Pine wood particles were treated with effluents from the wood-board manufacturing industry or from a communal clarification plant, and the effect of these treatments on aldehyde emissions of wood material was tested. Pine wood strands were treated in the same manner and strand boards were produced from the treated material on a laboratory scale. The 28-day volatile organic compound emissions of the boards were determined in a microchamber using Tenax-TDAS/GC-MS analytics. Boards made from treated strands exhibited significantly lower aldehyde emissions compared to control boards. Analyses of microflora and of wood extractives confirmed that microbial metabolism in industrial effluents consumed unsaturated fatty acids (UFAs) present in wood. As UFAs are the source of aldehyde emissions due to auto-oxidation, the aldehyde emission was consequently reduced. A routine treatment of wood raw material with properly chosen industrial effluents may therefore be regarded as a cost-reducing and efficient method for the utilisation of industrial waste waters.

The solution behavior and molecular conformation of sodium lignosulfonates (NaLS) in saline solution has been studied by means of static and dynamic light scattering (LS stat and LS dyn ). Results show that the salt content must be larger to eliminate the slow mode in LS dyn analysis of NaLS than that of the theory, and this discrepancy can only be explained by a modified microgel model. The higher salt amount is needed for the formation of a strong ionic gradient field between surface and the inner part of NaLS, which forces counter ions to penetrate into the inner part of NaLS to screen the small amount of charges. The NaLS single molecular shape can be described by an oblate spheroid based on the absolute molecular weight M w and diffusion coefficients D . The best fitting result is semiaxis a =1.6 nm and axial ratio r =3.5, D =5.73×10 -7 cm 2 s -1 , and the corresponding M w =1.7×10 5 g mol -1 .

Chemical and physical characteristics of wood from six European populations of Picea abies were investigated taking into consideration their genetic differentiation determined by four microsatellites markers. The growth conditions of investigated spruce trees differed significantly. As a consequence, several adaptations were observed in samples from varying environments. The adaptation mechanisms include a variation to the annual rings morphology as well as the physical properties of the wood. It was proved that some properties, such as wood density or latewood ratio, are strictly correlated to the environmental variables. Results show that trees from geographically distinct populations present some diversity in the genotypes. It was also noticed that some trees did not share their genetic profile with other plants from the same location due to high intrapopulation variability. Samples from Finland possessed the lowest level of internal differentiation, while samples from northern Poland presented the lowest allele richness and were most divergent from the others. It was not possible to correlate any wood properties (chemical or physical) to genetic features of the population due to high intrapopulation diversity.

The biomass/plastic ratio in wood plastic composites (WPCs) has been evaluated because of the great practical importance of this topic. To this purpose, FTIR spectra of 59 polypropylene (PP)-based WPCs from three biomass species (Chinese fir, poplar, and bamboo) were recorded and the spectral dates were evaluated by means of the partial least squares regression (PLSR) approach aiming at the prediction of the biomass/PP ratio in the WPCs. The results of the full cross-validation of the data showed that first derivative spectra corrected by standard normal variate (SNV) yielded the optimal model for prediction of the WPC composition. For both biomass and PP prediction, the coefficients of determination ( R 2 ) of external validation were above 0.94. The standard errors of prediction (SEP) were between 1.38 and 1.39. And the ratios of performance to deviation (RPD) were about 4.20. The relative prediction errors in this context were lower than ±6%. FTIR combined with PLSR is a useful tool for a rapid and reliable estimation of the biomass and PP contents in different types of PP-based WPCs.

The aim of this study was to enhance the water repellency and dimensional stability of thermally modified wood by combining the preimpregnation of paraffin wax emulsion. To achieve this, Southern pine (SP; Pinus spp.) samples were first impregnated with paraffin wax emulsion (with 2.0% solid content) and then subjected to thermal modification (TM) in an oven at 180°C and 220°C for 4 and 8 h. The contact angle (CA), surface free energy, water absorption rate (WAR), anti-swelling efficiency (ASE), and bending properties of the control and modified samples were investigated. Moreover, the chemical and morphological alterations were analyzed by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Both the wax impregnation and TM decreased the surface wettability, water absorption, and tangential swelling, while the combination of wax and thermal treatment exhibited the best water repellency and dimensional stability, indicating the synergism between the two procedures. However, the wax preimpregnation did not affect the mechanical properties of thermally modified wood. The FTIR, SEM, and XPS analyses confirmed that the synergistic effect is mainly due to the redistribution of the paraffin wax during TM rather than its impact on the chemical changes caused by thermal degradation.

The fracture behavior of bond lines in hardwood has been studied. The joints of a phenol resorcinol formaldehyde (PRF) resin and a one-component polyurethane (PUR) adhesive with European beech wood ( Fagus sylvatica L.) adherends were examined for their fracture toughness ( K c ). The initial crack tip was placed directly in the adhesive as a thin silicon film. Thereby, the examination of the bond line, and not the solid wood, can be assured. Five different load angles were applied, from fracture mode 1 (M1) to mode 2 (M2), with an Arcan test mount. Additionally, three sample series conditioned at the relative humidities (RH) of 50%, 65%, and 95% of the surrounding air were tested. The results clearly show an increasing K c of both adhesives with increasing shear stresses. This observation is valid for all RHs, but the differences decrease with increasing RH. The moisture dependency is more pronounced in PUR than in PRF glue joints. PUR generally shows a lower K c than PRF, with the only exceptions being K I,c and K II,c in dry climate. The subsequent crack propagation in the PRF samples mainly takes place in the wood adherend, whereas, in the PUR samples, the cracks remain within the bond line (adhesive failure). Nevertheless, the performance of PUR glue joints is not worse than that of the solid wood, which can be attributed to the ductile behavior of the adhesive.

Removing water from wood is a critical requirement for applications in building and construction and for chemical modifications. Normally, green radiata pine ( Pinus radiata D. Don) timber, with a moisture content (MC) range at harvest between 150% and 200%, is kiln dried to below fiber saturation point (FSP) to 10–14% MC. In the present work, a physical-chemical-mechanical dewatering process is presented, which involves pressure cycling with supercritical CO 2 to remove water to near the FSP. When the CO 2 was cycled from ∼4 MPa into the supercritical state, at pressures up to 20 MPa, specimens of cross-sectional dimensions of up to 52 mm were successfully dewatered from a MC of 174%, typical of the green state, to approximately 39% in seven cycles. The specimens with the smallest cross-sectional dimensions dewatered more slowly than the larger specimens. Preheating the green wood before loading it into the dewatering vessel increased the rate of dewatering. The final MCs were similar in all experiments and were independent of specimen dimension (15–52 mm) or preheating temperature between 40°C and 60°C. Pressure-temperature phase diagrams show that it is necessary to compress the CO 2 to the supercritical state for efficient dewatering. Diffusion rates and solubility of CO 2 in sap were important, but channel opening within specimens was proposed to be a critical factor in the dewatering process. The reason why pressure-based experiments remove water from wood to an MC greater than the established FSP of 30% is not yet clear.

From modern buildings to public spaces are made of concrete, steel, and glass. These materials increase propagation of sound and the reverberation time. Therefore, furniture should be good sound absorbers in such places. The objective of this study was to ascertain acoustic properties of wood-based materials by determining normal acoustic impedance on the surface and sound absorption coefficients. Experiments were carried out on 17 types of wood-based materials commonly employed in furniture design and manufacture. Investigations were conducted based on the transfer-function method. It was demonstrated that for frequencies between 125 and 500 Hz, the highest capability of sound absorption was determined of low surface layer density and high porosity. Honeycomb panels with paper core absorbed better sounds in the range between 1 and 2 kHz. Panels of considerable external surface irregularities were characterized by the most favorable acoustic properties for the frequency of 4 kHz.

Diffusion of chemicals and ions through the wood cell wall plays an important role in wood damage mechanisms. In the present work, free diffusion of ions through wood secondary walls and middle lamellae has been investigated as a function of moisture content (MC) and anatomical direction. Various ions (K, Cl, Zn, Cu) were injected into selected regions of 2 μm thick wood sections with a microinjector and then the ion distribution was mapped by means of X-ray fluorescence microscopy with submicron spatial resolution. The MC of the wood was controlled in situ by means of climatic chamber with controlled relative humidity (RH). For all ions investigated, there was a threshold RH below which the concentration profiles did not change. The threshold RH depended upon ionic species, cell wall layer, and wood anatomical orientation. Above the threshold RH, differences in mobility among ions were observed and the mobility depended upon anatomical direction and cell wall layer. These observations support a recently proposed percolation model of electrical conduction in wood. The results contribute to understanding the mechanisms of fungal decay and fastener corrosion that occur below the fiber saturation point.

A novel method for the preparation of bamboo fibers (BF) has been investigated that includes crushing, rolling, and other combing techniques with 1,4-butanediol as a dispersant. The fibers were treated by oxygen plasma to improve their interfacial adhesion to unsaturated polyester (UPE) resins. Composites were prepared from the plasma treated fibers (BF tr ) and UPE by hand lay-up compression molding. BF tr significantly increased the tensile strength, flexural strength, and flexural modulus of the resulting BF-UPE composites. Dynamic mechanical analysis indicated that the plasma treatment essentially increased the storage modulus and glass transition temperature of the composites. The damping parameter of the composites showed a decreasing trend in the glassy region, while the opposite was true for the rubbery region. X-ray diffraction analysis indicated that the treatment did not change the crystal structures within the fibers but increased slightly their crystallinity indices. X-ray photoelectron spectroscopy analysis revealed that the surface of BF tr had a higher oxygen concentration and oxygen/carbon ratio than that of BF. The scanning electron microscopy graphs of the tensile-fractured surface of the composites demonstrated an improved interfacial adhesion between BF tr and UPE resins.

Fungal decay alters the composition, microstructure, and mechanical properties of wood cell walls. To understand better the structure-function relationships during fungal decay, selected annual rings of fungal deteriorated Scots pine sapwood were analyzed in terms of their composition, microstructure, and micromechanical properties. The datasets were acquired separately for earlywood and latewood concerning the S2 cell wall layer and the cell corner middle lamella (CCML) and analyzed by means of principal component analysis and partial least squares regression analysis. Links between cell wall stiffness and hardness and the composition and microstructure could be established. Increased mechanical properties in the CCML, as obtained by nanoindentation, were correlated to the degradation of pectins. In the S2 layer, the altered data were related to the degradation of hemicelluloses and lignin modification during fungal decay.

The contraction along the longitudinal direction of Yezo spruce has been examined. The lignin and hemicelluloses (matrix) were removed from the samples with acetic acid and H 2 O 2 for different treatment times, and by this way the matrix content of the samples was diminished step by step. Then the chemically pretreated samples were submitted to aqueous NaOH treatments with varied concentrations. Mechanically isolated tracheids with the same matrix content as wood samples were also NaOH treated. The aim was to detect the longitudinal contraction behaviors of these samples as a function of the degree of matrix removal and the severity of NaOH treatment. The contraction behaviors of the samples were clearly depended on the NaOH concentration as well as on content and composition of the matrix. The differences in contraction behavior are due to the restrictive forces caused by matrices between cellulose microfibrils (CMFs) or between tracheids that prevent the contraction of CMFs also in the longitudinal direction. This is the reason why it is difficult to convert cellulose I to cellulose II in wood cells.

The Young’s modulus (modulus of elasticity, MOE) in the longitudinal (L) and radial (R) directions and the shear modulus (SM) in the LR plane of Douglas fir were determined by the flexural vibration (FV) tests under the free-free condition based on Timoshenko’s vibration equation. In the tests, the height/length ( H / L ) ratio was varied from 0.05 to 0.3. In addition, the test data were analyzed numerically and the effectiveness of Timoshenko’s equation was examined. The MOE and SM were calculated based on the rigorous and approximated solutions of Timoshenko’s equation. The inaccuracy of the approximated solution was enhanced when the H / L ratio of the specimen was too large. In contrast, the rigorous solution enabled the accurate calculation of these moduli in a wider range of length/depth ratios than the approximated solution.

A hypothesis for explaining the differential anisotropic shrinkage behavior of wood has been proposed, and it was based on the differences in the cell wall ultrastructure. The starting point of the consideration is that wood shrinkage is governed by its chemical composition, ultrastructure, and gross anatomy. It is also well known that the transverse shrinkage anisotropy of earlywood (EW) is more pronounced than that of the latewood (LW). In the paper, the cell wall ultrastructure and shrinkage anisotropy has been related to each other, and to this purpose, a set of crystallographic texture descriptors was applied. The descriptors are based on X-ray diffraction (XRD) experiments conducted on matched EW samples from different growth rings of Scots pine. The range of the microfibril angle (MFA) was identified. The ratio of the maxima of inverse pole figures (IPFs) of both the tangential (T) and radial (R) directions was determined. The ratios quantify the inhomogeneity of the spatial arrangement of the ordered areas. The results of the study clearly indicate that the transverse shrinkage of wood is governed mostly by a specific ultrastructural organization of moderately organized cell wall compounds.

Electron paramagnetic resonance was used in conjunction with X-ray fluorescence spectroscopy to quantify total copper and reacted copper retentions in MCQ and MCA treated Canadian red pine sapwood and western hemlock heartwood. Total copper retentions were distinctly different between earlywood and latewood of both softwood species examined. Earlywood of red pine sapwood had higher total copper content than the latewood, while western hemlock heartwood had higher total copper contents in latewood than earlywood. The reacted copper concentrations were similar in earlywood and latewood, reflecting a similar capacity of each to solubilize and complex the reacted copper.