Volume 59, Issue 4

Silver birch ( Betula pendula Roth) wood was subjected to bleaching with acidic hydrogen peroxide solution. The color change and chemical changes occurring on bleaching were investigated by CIELab color measurements and UV-Vis, FTIR and UVRR spectroscopy. With bleaching, the color of birch wood changed notably towards white, less red and more yellow, revealed by the CIELab color measurements, however, followed by notable yellowing in 343 days. The chemical changes occurring with the bleaching treatment in the xylem of birch, demonstrated by UV-Vis, FTIR and UVRR spectroscopy, indicated degradation of aromatic structures with a simultaneous increase in relative amounts of unconjugated carbonyl structures. The results indicate that the degradation of aromatic structures involved opening of the aromatic ring possibly leading to the formation of muconic acids or other low molecular weight products rich in carbonyl structures. In addition, in birch wood subjected to bleaching treatment with acidic hydrogen peroxide solution, syringyl structures provided favorable sites for the degradation of aromatic structures.

Samples of Pinus sylvestris were treated with different reagents bearing isocyanate, carboxylic anhydride or oxirane functions to induce reaction with the OH groups of the various components of wood. Conditions were optimised to achieve maximum grafting. When the reagents also carried a polymerisable function, a monomer (styrene or methyl methacrylate) was incorporated into the wood morphology after the derivatisation reaction. Subsequent radical polymerisation produced chemical incorporation of some of the resulting macromolecules. The properties of the doubly modified samples were assessed using a wide variety of tests. Both the hydrophobic character and the density increased considerably, suggesting improved lifetime and extended domains of application.

The chemical modification of maritime pine sapwood ( Pinus pinaster Soland) with 3-isocyanatopropyltriethoxysilane (IPTES) and its subsequent hydrolysis were investigated. The formation of urethane linkages after the carbamoylation reaction was confirmed by Fourier-transform infrared (FTIR) spectroscopy. The weight percent gain (WPG) obtained was found to be commensurate with the quantity of IPTES in the reagent solution. Swelling measurements combined with scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis showed that the reaction occurred within the wood cell walls. Hydrolysis of the grafted triethoxysilane ends in highly carbamoylated wood was also envisaged: the modifications generated after prolonged contact with water were studied by FTIR spectroscopy and 13 C and 29 Si nuclear magnetic resonance cross-polarisation with magic-angle spinning (NMR CP MAS) analysis. The chemical environments found for silicon (Si–OH, Si–OEt or Si – OSi) before and after hydrolysis were thus identified and a schematic representation of the silicon structures most often encountered in modified wood was proposed.

Spent sulfite liquors (SSLs) were fractionated by two common separation techniques: amine extraction and ultrafiltration. The lignin fractions obtained were characterized with respect to their elemental composition, functional groups and molecular weight distribution. The results of size exclusion chromatography indicate a broad molecular weight distribution of the lignosulfonates (LS). Irrespective of the separation technique used, a small LS fraction with high molecular mass and low degree of sulfonation was obtained, while most of the lignosulfonates have much lower molar masses and a much higher degree of sulfonation. Both separation methods offer the opportunity to extract high-purity LS fractions; however, compared to amine extraction, ultrafiltration provides additional information about the molecular weight distribution of the SSL components without application of other analytical techniques.

A few lignans, that is, 7-hydroxymatairesinol, secoisolariciresinol, lariciresinol, and nortrachelogenin, predominate in a large proportion of the industrially important softwood species used. Some other lignans, of which some still are unidentified, are also present in lower amounts. Softwood knots, i.e., the branch bases inside tree stems, commonly contain exceptionally large amounts of free aglycone lignans, which has provided a great opportunity to isolate sufficient amounts of softwood lignans for structural characterisation. Here we present the identification and characterisation of two new 9-epimers of 7-hydroxy divanillyl butyrolactol lignans, (7 S ,8 R ,8′ R ,9′ R )-4,4′,7-trihydroxy-3,3′-dimethoxylignano-9′,9′-lactol and (7 S ,8 R ,8′ R ,9′ S )-4,4′,7-trihydroxy-3,3′-dimethoxylignano-9′,9′-lactol, in knotwood of Colorado spruce ( Picea pungens ), from tentative GC-MS analysis to final determination of the structure by NMR spectroscopy and X-ray analysis. Further analyses have verified the occurrence of these lignans, which were earlier incorrectly addressed by our group as isomers of liovil, in several spruce, pine, and fir species.

Matairesinol and pinoresinol were isolated from sugisapwood 40 days after felling. These lignans were not detected in the heartwood. Accordingly, they are probably the result of post-mortem biosynthesis in sapwood parenchyma cells.

Wood is thermally modified by heating and steaming in order to change its properties, e.g., to improve the biological resistance and to increase the hardness of wood. The structure of thermally modified Scots pine ( Pinus sylvestris ) was studied using wide-angle, small-angle and ultra-small-angle X-ray scattering methods. Modification temperatures varied from 100 to 240°C. No marked changes in the microfibril angle distribution were observed. The mass fraction of crystalline cellulose in wood (the crystallinity of wood) and the size of cellulose crystallites increased above 150°C. After modification at 230°C for 4 h the thickness of the cellulose crystallites increased from 3.1 to 3.4 nm. Thermal modification had no effect on the orientation of the voids, but an increase in the porosity of the cell wall was observed. The distance between cellulose crystallites was approximately 4.7 nm in hydrated wood and a decrease in order between microfibrils was observed at 160–200°C.

The influence of inhomogeneity on acoustic velocity measured by a resonance-based WoodSpec acoustic tool and a transit-time-based Fakopp-2D tool was investigated. Four laminated panels with different degrees of inhomogeneity were prepared and acoustic velocities were measured using both tools. Velocities measured by the Fakopp-2D tool were always higher than those measured by the WoodSpec tool in all panels. The difference in the two velocities was found to vary depending on the magnitude of inhomogeneity. It was demonstrated that the velocity measured by the resonance frequency obeys the law of mixtures and is controlled by the volume-weighted average stiffness of the material. In contrast, the velocity measured by the Fakopp-2D tool was the velocity of the pulse that first reached the detector travelling at the dilatational speed.

A parallel-plate rheological analysis was developed for two types of cross-linking poly(vinyl acetate) latex films: solid freestanding films (neat), and solid films bonded directly to wood substrates (composites). The composite sample glass transition was increased by 5°C relative to the neat films, suggesting a strong interaction through polymer adsorption. Time-temperature equivalence was used to evaluate the mechanical response and the distribution of relaxation times in both systems. The resulting master curves revealed significant differences in the mechanical response during the glass transition: the neat films exhibited a 2.5–3-decade change in storage modulus and a damping factor of 1.65, while the composite samples showed a much smaller transition (approx. 0.3 decades and tan δ=0.4, respectively). The coupling model of Plazek and Ngai adequately described segmental relaxations in the glass transition. It was found that wood caused a small but significant decrease in segmental coupling (n=0.32±0.01) relative to that of the neat PVAc films (n=0.37±0.01). This finding was independently confirmed by directly fitting the Gram-Charlier statistical model to evaluate the distribution breadth. That wood caused an increase in the poly(vinyl acetate) glass transition, but a decrease in the related segmental coupling seems counterintuitive. The decrease in segmental coupling may result from reduced cross-linking in the composite films relative to the neat films; perhaps wood absorbs water-soluble reactive chains that would otherwise increase cross-linking in the neat films.

This study investigated the limitations of certain attributes for use in detecting internal defects using ultrasonic methods in spruce dimension lumber. Wave propagation in the radial direction and the effect of induced defects on ultrasonic wave characteristics were examined. Ultrasonic velocity, a parameter often applied, was found to be ineffective due to changes in wavelength and frequency when large defects were present. Amplitude, peak frequency magnitude and the area under the frequency spectra showed statistically significant differences between clear and defect-bearing samples, but among-sample variation was found to be too high because of localized density differences and microstructure, so that these methods were not consistently reliable. When sound intensity level was calculated, the variation among samples decreased and distinctions could be made between clear and defect-bearing wood, both within and among the samples tested. Certain attributes of the frequency spectra also showed clear changes with the introduction of defects.

The object of this study was to measure basic wood properties when water in wood is lost by heating under high temperature and high humidity. Using Sitka spruce ( Picea sitchensis Carr.) specimens with dimensions of 110 mm (R)×25 mm (L)×8 mm (T), temperature and weight were measured and free-free flexural vibration tests were conducted in water vapor at 115–150°C and 75–98% relative humidity. The results were compared to those at high temperatures without humidity control under atmospheric pressure. Early in the drying process, the resonance frequency and loss tangent showed a minimum and maximum, respectively. Temporal changes in the temperature, moisture content and vibrational properties were similar to those in heating without humidity control, while the specific Young's modulus and loss tangent during the drying processes were much smaller and greater, respectively, than those in heating without humidity control. Hence, we concluded that the wood was remarkably softened by high temperature and moisture.

The elastic properties of Norway spruce were studied by means of ultrasound. Samples were from stems that were grown either at a medium- or a high-fertility site in Finland. The stiffness modulus was determined in the longitudinal, radial, and tangential directions as a function of the distance from the pith using 1-mm-thick samples. Tangentially cut samples contained only earlywood, while radially and longitudinally cut samples contained both earlywood and latewood. The stiffness modulus in the longitudinal direction for Norway spruce grown at a medium-fertility site increased with distance from the pith from 6±1 to 8.5±1 GPa. This parameter increased as the mean microfibril angle decreased. In the radial and tangential directions, the stiffness modulus was nearly constant, at 1±0.15 and 0.35±0.04 GPa, respectively. The longitudinal stiffness modulus of fast-growing clonal trees, which contained a large share of juvenile wood and were growing on a fertile site, was ca. 30% smaller (4±1 GPa near the pith and 6±1 GPa at the age of 12 years) than that of trees on a medium-fertility site. No difference was found in the radial and tangential stiffness modulus between stems grown at the two sites.

In order to establish integrated control strategies of wood degradation, a systematic survey of basidiomycete decay fungi colonizing various wood products in service is a prerequisite to increasing the service life of wood products. As a first step, we initiated a thorough survey of basidiomycete decay fungi colonizing playground wood products. For accurate fungal identification, traditional methods were complemented with molecular methods, including a BLAST search for large-subunit 28S rDNA sequences in Genbank and phylogenetic analysis. A total of 132 basidiomycete fungi, including 30 different fungal taxa, were isolated from 35 playgrounds in 15 different areas. Eight species, Bjerkandera adusta, Ceriporia lacerata, Gloeophyllum trabeum , Peniophora sp., Phanerochaete sordida, Schizophyllum commune, Sisto-trema brinkmannii , and Trametes versicolor , were predominantly isolated. A combination of traditional and molecular tools allowed a more detailed identification and diversity.

Until recently, most research on the leaching of preservatives from treated wood was conducted in the laboratory. Although these studies have contributed to the understanding of leaching, the data generated under controlled conditions often do not apply to leaching during natural exposure and weathering. In addition, little is known about the effects of climatic variables and long-term emission rates. This paper examines leaching of chromated copper arsenate (CCA) from lumber exposed above ground to 685 mm of precipitationduring 351 days of natural weathering. Stepwise multiple regression analysis revealed relationships between leaching and a number of treatment and climatic variables, including: species of wood, initial preservative loading, amount of precipitation, average air temperature, average light intensity, pH and duration of rain event. Regression models explained approximately 30% of the variation in chromium and arsenic leaching and 44% of the variation in copper leaching.