Volume 62, Issue 3

Topochemical detection of lignin and phenolic compounds was carried out at subcellular level in tension wood fibres of maple ( Acer spp.), beech ( Fagus sylvatica ) and oak ( Quercus robur ) by means of cellular UV-microspectrophotometry (UMSP) and confocal Raman microscopy. UMSP field scans at 278 nm revealed the presence of aromatic compounds in the gelatinous layer (G-layer) in tension wood of all three species. Characterisation of the detected substances by point measurements from 240 nm to 400 nm revealed a plausible relationship to by-products from the lignin biosynthesis pathway. Raman spectra, recorded from different regions within the G-layer, showed a high affinity to spectra of lignins. The degree of aromatic compounds in the G-layer of oak tension wood fibres was approximately three-fold higher than that in maple and beech. Moreover, the oak G-layer showed an accumulation of aromatic compounds towards the cell lumen up to 50% higher than that detected in the secondary cell wall. UMSP and Raman microscopy are considered valuable complementary methods for topochemical investigation on a subcellular level.

Wood products for exterior residential applications have long been protected with metallic preservatives. However, environmental and disposal concerns and governmental regulations have resulted in a growing trend to employ organic systems based on relatively benign and expensive agrochemicals. To develop organic preservatives that have increased efficacy and lower cost, various groups are studying the biocidal and non-biocidal properties of extractives present in naturally durable heartwoods. In this study, we determined the fungicidal, free radical scavenger/antioxidant, metal chelation and Fe 3+ reducing properties of some flavones and flavonoid analogs and chromones. The results support our earlier hypothesis that the abiotic antioxidant, Fe 3+ reduction and subsequent metal complexation properties, in combination with the extractives’ fungicidal properties, all have a role in natural durability. Consequently, it may be possible to employ non-biocidal additive(s) with the above abiotic properties to enhance the efficacy of the relatively expensive organic agrochemicals used to protect wood.

Demand for the development of environmentally benign wood preservatives has increased significantly. To reduce the evaluation time of prospective candidates, reliable accelerated decay methodologies are necessary for laboratory screening of potential preservatives. Ongoing research at Mississippi State University has focused upon utilizing custom built equipment to measure stiffness losses in wood wafers after 4 weeks of fungal exposure as opposed to mass losses in blocks after 12 weeks. Stiffness loss as a measure to quantify the extent of biodeterioration may allow detection of incipient decay. The resistance of untreated and treated southern yellow pine and radiata pine ( Pinus radiata ) sapwood wafers to biodeterioration by brown rot ( Neolentinus lepideus , Gloeophyllum trabeum and Postia placenta ) and white rot ( Trametes versicolor and Irpex lacteus ) fungi was investigated by measuring stiffness. From the data collected percentage stiffness losses were calculated based upon modulus of elasticity. It is a potentially accurate alternative to the “secant modulus” at a deformation equal to 5% of the specimen height calculation generally performed.

Thermo-hygro-mechanical (THM)-densified wood is more resistant to colonisation and degradation by brown-rot fungi than untreated wood. Colonisation and degradation by soft-rot fungi was investigated in treated Norway spruce ( Picea abies ) and treated beech ( Fagus sylvatica ) to assess their suitability for utility class 4. Three different treatments were applied: thermal-hygro (TH) treatment, mechanical densification and THM-treatment including densification and post-treatment under saturated steam conditions at different temperatures. For comparison, additional wood specimens were treated with two concentrations of a chromium-copper (CC) wood preservative. After 32 weeks incubation, weight losses induced by soft-rot fungi were lowest in wood treated with CC. Highest weight losses were recorded from TH-treated wood, in which soft-rot erosion attack (type 2) was exclusively observed in spruce. In comparison to controls, significantly lower weight losses by soft-rot fungi were recorded in THM-treated spruce wood, but no such differences were found in beech wood. Microscopical examination showed that in THM-treated wood of spruce, soft-rot type 1 commenced from the outer wood surfaces and cavity formation was not found in deeper regions of the wood samples. THM-treated beech wood was more susceptible to degradation than that of spruce which can be partly explained by the higher syringyl lignin content in beech wood, which is more susceptible to all kinds of degradation. Hyphal colonisation and soft-rot was facilitated within deeper regions of beech wood mainly in the non-occluded lumina of parenchyma cells in multiseriate xylem rays. It can be concluded that TH-treated spruce wood and THM-treated beech wood is susceptible to soft-rot and therefore inappropriate for utility class 4.

FT-NIR spectroscopy equipped with a fiber optic probe was used to predict the mass loss caused by a brown-rot fungus ( Coniophora puteana) in Scots pine heartwood. Because decay tests are impractical for generating reference data for the calibration of prediction models, the possibilities of using the concentration of heartwood extractives as a reference variable instead of mass loss was studied. The material investigated covered a wide range of natural variation in durability and diffuse reflectance infrared Fourier transform spectra were recorded from the cross section of 41 pines. The partial least square (PLS) regression models were found to be satisfactory for prediction of the mass loss and the concentration of extractives (total phenolics, resin acids, pinosylvin and pinosylvin monomethyl ether). It was concluded that FT-NIR spectroscopy has the potential to become a tool for the decay resistance grading of Scots pine heartwood timber, especially if the prediction models will be based on heartwood extractives.

Red pine ( Pinus resinosa Ait.) sapwood samples treated with alkaline (amine) copper quaternary (ACQ) were conditioned at different temperatures and under wet or dry conditions to evaluate the stability of copper (Cu) to leaching and conversion of divalent copper (Cu-II) to monovalent copper (Cu-I). Significant Cu-II was reduced to Cu-I during post-treatment stabilization, especially at elevated temperatures (105°C and 120°C). The percent conversion to Cu-I was higher at lower retentions; in some cases, at low retentions and high fixation temperatures, all of the cupric Cu was reduced to Cu-I, raising the possibility of reduced activity of Cu as a biocide when high temperature conditions are used to fix ACQ treated wood. However, exposure of wood to a leaching procedure (rewetting, re-drying) generally resulted in a significant component of the Cu-I in wood being oxidized back to Cu-II. Steaming of weathered ACQ treated wood at 120°C also converted significant amounts of Cu-II to Cu-I.

A new waterborne CuSO 4 ·5 H 2 O-based formulation containing proteins from animal plasma SOLUTEIN (0.1%) as additive was investigated. Scots pine sapwood powder, cellulose and lignin were impregnated with solutions containing 0.1% and 2.5% copper (w/v). After impregnation, the samples were additionally treated by air-drying at 100°C or by tannic acid for denaturation of the proteins. Copper concentration was determined by atomic absorption spectroscopy and electron paramagnetic resonance (EPR). Copper introduced into wood by impregnation and eliminated by leaching was controlled. The maximum retention of 5.83 g kg -1 in wood was obtained when wood was treated with tannic acid (2.5%) after impregnation. For a formulation containing more than 0.5% of CuSO·5 H 2 O, precipitation of the salt in wood appears. Five different EPR spectra appeared in wood, cellulose and lignin after treating with SOLUTEIN and with tannic acid.

Electron paramagnetic resonance (EPR) spectra were recorded for copper(II) ions in cellulose, lignin and pine sapwood impregnated with a water based formulation containing CuSO 4 ·5 H 2 O, tannic acid and animal protein SOLUTEIN. EPR parameters were derived from computer-simulated spectra. The parameters were interpreted in terms of molecular orbital theory giving coefficients of spin delocalization onto ligands. Five different spectra of chemically fixed complexes were identified. The complexes were octahedral with a different degree of elongation. For a copper concentration higher than approximately 0.5%, the additional EPR signal from the precipitated CuSO 4 ·5 H 2 O salt appears. Two possible coordination sites are proposed for fixed copper complexes in cellulose structure and a single site is proposed for copper in a lignin. These complexes are different from the copper complex in wood, where Cu(H 2 O) 4 O 2 octahedral complex exists with apical coordination to two oxygen atoms of deprotonated hydroxyl groups of polymeric units. When tannic acid is added to the impregnating solution, copper ions are strongly coordinated in a square-planar geometry of CuO 4 and are easily leached. The copper-SOLUTEIN complex yields a distinguished EPR spectrum only in the impregnating solution, but not in the wood. Except for the copper(II) EPR spectra, where the signals from free radicals were detected in wood and lignin with a concentration in the order of magnitude of 10 17  g -1 dependent on wood treatment.

The following pyridinium-based ionic liquids (ILs) have been successfully tested as components of potential wood preservatives: 1-alkoxymethyl-3-dimethylaminopyridinium chlorides, 1-alkoxymethyl-4-dimethylaminopyridinium chlorides, 1-alkoxymethyl-3-dimethylaminopyridinium acesulfamates and 1-alkoxymethyl-4-dimethylaminopyridinium acesulfamates. These ILs are new biocides that penetrate well into wood. The tested pyridinium ILs with an alkoxymethyl substituent, consisting of 8, 9 or 10 carbon atoms, exhibited fungicidal activity against the basidiomycetes Coniophora puteana and Trametes versicolor and the blue-stain fungus Sclerophoma pityophila. The effective and lethal doses were measured by the agar-plate method and the toxic values, before and after leaching according to EN 84, were determined based on the EN 113 block method. The doses and toxic values of tested 1-decyloxymethyl-4-dimethylaminopyridinium chloride and acesulfamate were comparable with benzalkonium chloride and didecyldimethylammonium chloride. The ILs tested were largely unleachable from wood by water. The mechanical properties of wood treated with the former two ILs were lower than natural wood. Wood treated with the chloride and acesulfamate was, however, characterized by lower absorption of free water than the control wood. Only in the case of treatment with acesulfamate was the hygroscopicity of treated wood distinctly lower than that of control wood. The durability of wood was increased by 1-decyloxymethyl-4-dimethylaminopyridinium chloride and acesulfamate.

The pruned part of a beech ( Fagus sylvatica ) branch was imaged by a 3D spin-echo magnetic resonance imaging (MRI) technique to visualize change in structure and water content in the tissues. Proton density-weighted MR images of intact tissues confirmed high moisture content (MC) associated with high MRI signal in the pith, xylem rays and earlywood vessels, as well as in the cambial zone with current annual xylem and phloem increment. MRI images derived from the 3D datasets showed a previously unreported moisture-related structural response of the beech branch to wounding. An extensive wound tissue with a high MRI signal at the wound edge was a conspicuous new structure clearly visualized by 3D MRI. MRI revealed that the xylem at the wound was dehydrated in a cone-shaped pattern extending approximately 4.5 mm deep into the branch. Dehydration was delimited from the underlying sound wood by a layer, corresponding to the reaction zone, of tissue with a high MRI signal and hence high moisture content. Moisture content of these reaction zones in beech determined by MRI were greater than in healthy wood by factors of 1.3–1.8. Accordingly, in the margins of wounded beech wood not only cell wall alterations can be observed, but also an intensive water accumulation, which is probably an integral part of the protective mechanism for the underlying sound wood.

Arabinoxylans from corn cob and oat spelt were studied in sorption experiments onto bleached and unbleached softwood kraft pulp. The corn cob (CC) xylans were produced by steam extraction (SE-CC) and alkaline extraction (NaOH-CC), while the oat spelt xylan (NaOH-OS) was obtained by alkaline extraction. Both alkaline extracted xylans exhibited a high degree of polymerization (DP) (230–240), whereas the steam extraction induced a significant degradation resulting in DPs around 36. Investigation of the xylan addition mode revealed that adding xylan before beating of pulp is most effective for increasing the beating degree and the strength properties. The tensile and burst indices are improved by xylan addition over the whole range of beating degrees. In contrast to that, the tear strength is increased significantly for unbeaten pulps but declines after beating, compared to the reference. Xylan sorption rates are increased with prolonged beating. Highest sorption rates are observed for the NaOH-OS (12–32%) and lowest for the SE-CC xylan (6.6–14%). In general, the alkaline extracted xylans have a better performance, most likely as a result of their higher molar masses.

Wheat straw fibre is prepared by a thermomechanical (TM) refining system. This study investigated the effects of refining steam pressure (4, 6, 8 and 10 bar) and refiner speed (2500 and 3000 rpm) on the morphology and thermal properties of the resulting fibres. After TM refining, the fibres exhibited more surface irregularities and heterogeneities as well as decreased fibre length. The fine content decreased with increasing steam pressure, but the aspect ratio increased. The findings show that higher steam pressure (8 bar) results in more effective wheat straw refining. Refining lowers the pH. Thermogravimetric analysis showed that TM refining does not influence the thermal properties of wheat straw fibres. Weight loss has to be taken into account upon exposure to temperatures around 170°C. The silica content of the fibres was significantly reduced through refining.

Eucalypt wood ( Eucalyptus globulus ) was heated in an oven for 2–24 h at 170–200°C and in an autoclave with superheated and saturated steam for 2–12 h at 190–210°C. The chemical composition of untreated wood and thermally treated wood with different mass losses in the range of 1.1–11.9% was studied by summative analysis, and the composition of dichloromethane, ethanol and water extracts was determined by gas chromatography mass spectometry (GC-MS). The hemicelluloses degraded first, mainly regarding the arabinose and xylose moieties. Lignin degraded at a slower rate and cellulose was only slightly affected under severe treatment conditions. The extractive content increased first with heat treatment and decreased later on. Almost all of the original extractives disappeared and new compounds were formed, such as anhydrosugars, mannosan, galactosan, levoglucosan and two C 5 anhydrosugars. The most prominent lignin derived compounds were syringaldehyde, syringic acid and sinapaldehyde. The main difference between autoclave and oven treated samples was the appearance of more oxidized extractives for the oven treatment.

The relationship between inward and outward swelling of cell wall surfaces was examined. A formula was derived based on a cylindrical model of a wood cell. The equation clarifies that the slope of the swelling ratio of the whole wood versus moisture content is governed by a number of factors. This equation allows the examination of how the swelling direction of cell wall surfaces is determined during water adsorption. The swelling direction is given by the parameter Δh/Δr , where Δh is the increase of cell wall thickness as a result of inward and outward swelling and Δr is the outward increase.

The swelling of larch wood in 1-butanol, dimethyl sulfoxide, N,N-dimethyl formamide, ethylene glycol, ethanol, methyl cellosolve, 1-propanol and toluene was investigated at room temperature. The volumetric, tangential and radial swelling completion was lagging behind the liquid absorption process. The kinetic indices of swelling of larch wood were determined based on the equation of Kolmogorov-Erofeev. The volumetric swelling was related to molecular mass, molar volume, dielectric permittivity and integral heat of wood wetting. The anisotropy of wood swelling was characterized by the ratio of equilibrium tangential swelling to radial swelling ( α t ,/ α r ). It was demonstrated that α t ,/ α r is related to the dipole component of Hansen's parameter and cannot exceed the value 3.

Thermal conductivity is frequently determined by the hot plate method. The influence of the anatomical and morphological properties of fir wood ( Abies alba Mill.) was studied on the hot plate method and the mechanical treatment on the contact thermal resistance of the surface was addressed. It was confirmed that there is a contact thermal resistance between the surface of a specimen and the smoother metal plate of an experimental device. It amounted to 3.04×10 -3  m 2 K W -1 in the direction of wood fibres and, similarly, 2.96×10 -3  m 2 K W -1 in the transverse direction. A negligible contact thermal resistance – maximal 9% of the contact thermal resistance between the wood specimen and the metal plate – was determined at the contact of two wood surfaces. It is ascribed to the better fit of two wood surfaces compared to the fit of the wood surface with a smoother metal one. Irreversible morphological changes were determined in the real surface layers of mechanically treated test specimens. Abbot curves of real bearing profiles were additionally prepared, where the equality of longitudinal and transverse wood surfaces, as well as a sigmoid increase of bearing surface towards the inner wood tissue of test specimens was confirmed. The inverse proportional relation between the contact thermal resistance and the contact surface of wood was ascertained. The thermal conductivity of the combined and reintegrated composite of solid wood was invariable.