Volume 53, Issue 5

Under laboratory conditions basidiomycete and soft rot tests were carried out on more than 20 hardwood species and 3 softwood species together with reference species to evaluate their natural durability according to the European standard EN 350 part 1. The basidiomycetes tests were carried out using Gloeophyllum trabeum, Coniophora puteana, Poria placenta and Coriolus versicolor , all fungal strains in malt agar tests and in agreement with the EN 113. Such tests did not provide a solid basis to classify all wood species according to known durability classes (EN 350, part 2). There was only a distinct differentiation noted between those species belonging to the group with a durability classified 1 to 3 and those classified 4 to 5. Conclusively, only limited additional information on durability of tropical hardwoods was gained from brown rot tests. Despite both types of laboratory tests on soft rot, prescribed in ENV 807 (vermiculite and soil) which show the essential differences to the basidiomycete test results, it has not been possible to classify the durability subdivisions in a more substantial way. Adding to these tests the durability classification, based upon a field stake test (EN 252) and a greenhouse accelerated stake test, was also carried out. Using this last method, results can be gathered more rapidly and consequently confirm the efficiency of lab tests. Generally it is perceived that lab tests and accelerated tests are important tools in the prediction of the natural durability of wood. To further improve the predictability value, durability testing would be enhanced when using a hazard class orientation. Therefore the function of the conclusive end product can be identified in a more obvious way.

Specimens of Pinus sylvestris have been subject to decay by the brown rot fungus Coniophora puteana , the white rot fungus Phanerochaete chrysosporium , and to doses of γ irradiation sufficiently high to cause significant molecular damage. Specimens of Picea abies have been subject to decay by the brown rot fungus Postia placenta . The dynamic mechanical properties of the decayed and degraded materials have been assessed between −100 °C and 120 °C using in some cases a natural frequency instrument and in other cases a driven frequency instrument. The results obtained have allowed calculation of the temperature coefficients of modulus for the materials at various stages of decay or degradation, and these are relatively constant regardless of the history of the specimen. Such changes as do occur can be explained by modulus dependent frequency effects. The static mechanical properties of some specimens were also assessed by three point bending at 20 °C. Measured changes in dynamic stiffness and flexural modulus have been compared with the weight changes and the proportionality constant relating strength and stiffness loss to weight loss obtained for each situation. These show that in the case of fungal attack the dynamic stiffness falls more quickly than flexural strength, and that, as would be expected, the brown rot fungi are the more effective at reducing mechanical properties.

The aim of this study was to fix chromium chemically in wood from trivalent chromium solutions. Chromium(III) nitrate, chloride and sulphate salts were applied, both in aqueous and in methanolic solutions. To improve chromium fixation metallic zinc was used as a strong reductant to generate labile Cr(II) species from Cr(III), and base was added (NaOH for water and NaMeO for methanol). Aqueous solution reaction conditions were always acidic in spite of base addition, leading to unacceptable levels of wood degradation (e. g., weight loss), although relatively high chromium levels were attained in some cases. Methanolic solutions did not lead to wood degradation, and there was fixation of high levels of chromium. Although the addition of NaMeO seemed to improve chromium fixation, a chromium precipitate always formed, usually after a long reaction time (> 4h). Therefore the following experimental conditions for chromium fixation are suggested: alcoholic solution of Cr(III) chloride or nitrate, addition of metallic zinc, at reflux. To avoid using large amounts of zinc, Cr(III)-solutions can also be reduced electrochemically.

The possibility of using synchrotron radiation microbeam X-ray fluorescence (μ -XRF) for the determination of the morphological distribution of inorganic elements in wood has been investigated. A number of samples were analyzed and some of the results are presented in this paper. The new application of the method showed good results and it was concluded that the technique is useful for specific in situ metal ion analysis of wood. One of its special advantages is that it is a non-destructive method, which may allow analysis of the same sample before and after a chemical treatment. This study shows the natural distribution of a selection of metal ions in wood. Some differences in the distribution and amount of certain metals could also be observed in a sample that had been subjected to treatment with an EDTA-solution.

The composition of lipophilic extractives in the chloroform soluble fraction of the acetone extract from Eucalyptus globulus wood has been examined. The lipid extract was fractionated by solid-phase extraction on aminopropyl-phase cartridges into four different fractions of increasing polarity. The total lipid extract and the resulting fractions were analyzed by gas chromatography and gas chromatography-mass spectrometry, using high temperature capillary columns. The main compounds identified included sterols, sterol esters, fatty acids, steroid ketones, hydrocarbons and triglycerides. Minor compounds such as fatty alcohols, mono- and diglycerides, waxes and tocopherols were also identified among the lipids from E. globulus wood.

This study was to isolate and identify the antifungal compounds in the ethyl acetate soluble fraction of the methanol extractives of Taiwania ( Taiwania cryptomerioides Hayata) heartwood and to examine their antifungal activity. Five compounds were obtained by open column chromatography and HPLC and based upon the results from Mass, 1 H-NMR, and 13 C-NMR analyses. Their structures were identified, namely ferruginol, helioxanthin, savinin, taiwanin C, and hinokiol. According to the results of antifungal test, the order of antifungal index of these compounds for Coriolus versicolor (L. ex Fr.) Quel. was ferruginol > taiwanin C > savinin > hinokiol. For Laetiporus sulphureus (B. ex Fr.) Bond. it was taiwanin C > savinin > ferruginol > hinokiol.

Three stilbenes, pinosylvin (PS), pinosylvin monomethyl ether (PSM) and pinosylvin dimethyl ether (PSD), were extracted from white spruce (Picea glauca) , jack pine (Pinus banksiana) , and red pine (Pinus resinosa) pine cones, and their structures were confirmed by spectroscopic and chromatographic (HPLC, GC/MS, NMR and FTIR) analysis. PS, PSM, PSD or a 1:1:1 mixture of these stilbenes at concentrations of 0.1 % and 1.0 % were examined for their fungal inhibitory activity by two bioassay methods. Growth of white-rot fungi (Trametes versicolor and Phanerochaete chrysosporium) , and brown-rot fungi (Neolentinus lepideus, Gloeophyllum trabeum and Postia placenta) on agar media in the presence of each of the stilbenes or a 1:1:1 mixture inhibited growth of white-rot fungi, but slightly stimulated growth of brown-rot fungi. Soil-block assays, conditions more representative of those found in nature, did not correlate with those from the screening on agar media. PS, PSM, PSD or a 1:1:1 mixture of the three compounds at concentrations of 0.1 % and 1.0 % did not impart any significant decay resistance to white-rot fungi inoculated on a hardwood (Red maple). However under the same conditions, decay resistance was observed against brown-rot fungi on a softwood (Southern yellow pine). It appears that stilbenes at least partially contribute to wood decay resistance against brown-rot fungi.

The structure activity effects of 1-hydroxy benzotriazole and phthalimide derivatives as mediators for laccase were studied. Using a softwood kraft pulp it was shown that the N-hydroxy unit is a key component of 1-hydroxybenzotriazole for efficient laccase mediator delignification to occur. It was also found that the 1-hydroxybenzotriazole structure was very sensitive to substituent effects with respect to laccase-mediator delignification. Computational results from PM3 indicate that the bond dissociation energy, and electronic factors of the radical may contribute to the efficiency of the mediator for LMS delignification.

Cell-wall-associated oxidases extracted from the lignifying xylem of Sitka spruce and ash oxidise sinapyl alcohol at a greater rate than coniferyl alcohol and p -coumaryl alcohol (SA > CA > pCA). The enzyme from ash shows a marked preference, on a specific activity basis, for the oxidation of SA over CA and pCA (SA ≫ CA ≥ pCA) and has a particularly low affinity for the oxidation of coniferyl alcohol compared to the enzyme from spruce (SA > CA > pCA). This difference in monolignol preference between the spruce and ash enzymes may relate to their required functions during lignification, in that the hardwood enzyme would be supplied mainly SA and the softwood enzyme would be supplied mainly CA. The spruce enzyme also displayed a marked preference for the oxidation of sinapyl alcohol over sinapyl aldehyde even when the two compounds were presented in a mixture. Purified cell walls from the lignifying xylem of spruce could oxidise CA by the action of bound oxidase activity and dissolved oxygen (~ 240 μM) but CA oxidation was increased many fold by the action of the bound peroxidase activity and 240 μM H 2 O 2 . However, the initial dimeric and trimeric products of the peroxidase- and oxidase-catalysed reactions detected by liquid chromatography-mass spectrometry were the same and present in similar proportions. This indicates that the oxidation of CA by oxidase or by peroxidase proceeds via the same intermediates and occurs by a similar mechanism. Insoluble dehydrogenation polymers (DHPs) of CA were formed in similar yields by spruce extracts in the absence (oxidase activity) or presence (peroxidase activity) of H 2 O 2 . The peroxidase-catalysed DHPs and the oxidase-catalysed DHPs gave Fourier transform infra-red spectra with maxima that were characteristic of DHPs of CA. However, differences in the comparative intensities of some maxima suggest that the oxidase-catalysed DHPs were less condensed than the peroxidase-catalysed polymers. These findings are discussed with respect to the possible contribution of oxidases to lignin structure in developing wood.

Lignins obtained by atmospheric acetic acid delignification of rice straw, birch and fir were characterized by molecular weight, solubility and thermomechanical analysis, and by ultraviolet (UV), Fourier transform infra-red (FTIR) and 13 C-NMR spectroscopy. Rice straw lignins (rice lignins) were very different from birch and fir lignins. The former was difficult to dissolve in most tested solvents and infusible on heating, while the latter had a good solubility and fusibility. FTIR spectra indicated that the rice lignins had more conjugated and fewer unconjugated carbonyl groups than the wood lignins. 13 C-NMR spectra showed that rice lignins had more polysaccharides associated to the lignin and more p -coumaric and ferulic acid than the wood lignins. Concentrations of acetic acid and choice of catalyst (sulfuric or hydrochloric acid) had a considerable effect on the characteristics of rice lignins. Rice lignin obtained with 90% acetic acid than that obtained with 80% acetic acid, and the lignin obtained with sulfuric acid as catalyst than that obtained with hydrochloric acid, had lower molecular weight, better solubility, lower glass-transition temperature and lower UV absorptivity. 80% acetic acid delignified rice straw less effectively than 90% acetic acid.

Findings about anomalous high Klason residues of azobe ( Lophira alata ) heartwood prompted a search for methods of determination of non lignin-type polyphenols in lignin preparations. A four step procedure was performed: (1) ethylation of milled wood lignins (MWLs) from azobe and beech heartwood, (2) permanganate oxidation, (3) methylation, and (4) GC analysis of the oxidation products. Besides the well known degradation products of hemipinic, iso -hemipinic, and meta -hemipinic acid type, methyl-3,4-diethoxy-benzoate (compound I ) has also been detected among the oxidation products. The oxidation of beech MWL gave rise only to 0.4 mol % of I but azobe MWL yielded the remarkably high amount of 10.7 mol % of I . As lignins do not contain two adjacent aromatic hydroxyl groups, we concluded that I is of polyflavonoid origin. Hence the extraordinarily high Klason residues of azobe heartwood can be rationalized with large amounts of acid insoluble polyphenols which are an integral part of the azobe cell wall and which is also closely associated to MWLs. Ethylation followed by KMnO 4 oxidation is an effective tool to detect polyflavonoids in lignins.

Two independent spectroscopic methods are presented and compared for the quantitation of the phenolic hydroxyl groups in lignins. The combined information is used to further elucidate the character of the lignin samples examined. The UV method is based on the difference of the spectroscopic properties of the ionised and the nonionised phenol. The method using 1 H NMR spectroscopy is based on the exchange of phenolic protons in D 2 O. The difference in integrated proton intensities in the sample dissolved in DMSO and the sample with additional 20% D 2 O is proportional to the phenolic protons. The method based on UV spectroscopy uses differences in the maxima close to 300 nm and 350 nm of the sample dissolved in alkali and the neutral sample. The results using the two independent methods are in agreement for milled wood lignin, for kraft lignin and for model compounds carrying one aromatic hydroxyl group. For modified lignins and for model compounds with more than one aromatic hydroxyl group, the UV method gives too low values for phenolic hydroxyl groups. The combined results obtained by the two methods however provide information of the total amount of the phenolic groups and of the nature of the phenolic structure formed by the lignin refining.

The effective diffusion coefficient and mass transfer coefficient of Scot's pine and Norway spruce heartwood are calculated from the measured development of the internal moisture profiles of sawn timber during drying. Measurement is made using the oven-dry method. Calculation of both coefficients is based on using an existing timber drying simulation model to iteratively optimise the parameter values for the diffusion and mass transfer coefficients of prescribed functional form. The results show that the procedure employed is a feasible method to obtain numerical values for the internal and external transfer coefficients as functions of wood moisture content and temperature. The resulting diffusion coefficient and mass transfer coefficient are applicable in the whole moisture range between green and dry states in temperatures 20–80°C thus covering the whole process of medium-temperature wood drying.

To clarify the mechanism of the permanent fixation of compressive deformation of wood by high temperature steaming, stress relaxation and stress-strain relationships in the radial compression for Sugi ( Cryptomeria japonica D.Don) wood were measured under steam at temperatures up to 200°C. The stress relaxation curves above 100°C were quite different in shape from those below 100°C, showing a rapid decrease in stress with increasing temperature. In the stress-strain relationships measured above 140°C, the stress reduced as pre-steaming time increased when compared at the same strain. The recovery of compressive deformation (strain recovery) was decreased with steaming time and reached almost 0 in 10 min at 200°C. The relationship between the residual stress and the strain recovery at the end of relaxation measurements could be expressed by a single curve regardless of time and temperature. The permanent fixation of deformation by steaming below 200°C was considered to be due to chain scission of hemicelluloses accompanying a slight cleavage of lignin. In some cases, the increase in regularity of the crystalline lattice space of microfibrils or the formation of crosslinks between the cell wall polymers seemed to play an important role in the permanent fixation of compressive deformation.

This paper was designed to investigate the change of bending strength, bonding shear strength and surface fire-retardant (FR) performance of FR treated plywood after accelerated degradation treatment at elevated temperature (77 °C) and medium humidity (50%RH) condition. Furthermore, thermogravimetry analysis (TGA) and differential scanning curves (DSC) analysis were also conducted to explore their thermal degradation. PF-bonded Red meranti ( Shorea spp.) and radiata pine ( Pinus radiata ) plywood, FR chemicals of AF21 and Lee-An 302 were used. Results indicated that the bending strength and bonding shear strength of non-FR treated and FR treated plywood decreased linearly with the increase of treatment durations. After 80 days of accelerated degradation treatment, the reduction ratio ( %) of bending strength ranged from 6.5% to 33.4% and varied with treatment conditions, whereas 12.8% to 42.3% reduction ratios were observed in bonding shear strength. After subjected to accelerated degradation treatment FR treated plywood could meet the requirement of the third grade FR performance as specified by CNS 6532 standard except those treated with Lee-An 302 FR for 20 days and 40 days. Furthermore, based on TGA, the weight loss of FR treated plywood was found to be less than that of non-FR treated plywoods. After thermal degradation under 100°C, the residual weight of FR treated plywood was higher than that of non-FR treated plywoods.

The moisture related properties of wood-coating composites have been studied to evaluate the influence of coating penetration on the protection of wood against moisture. Pine sapwood samples were vacuum-impregnated with 7 pigmented and unpigmented coatings, both water and solvent borne. The retention and void filling of the coating have been determined. After drying, the samples were exposed to relative humidities between 33 and 98 % and to liquid water and equilibrium moisture content and dimensional changes were measured. The rate of swelling and moisture sorption has been measured, the latter was also used to calculate diffusion coefficients. The sorption isotherms were analysed by the Hailwood-Horrobin equation. In order to obtain additional information on the hygroscopicity of coatings, similar measurement were made on free coating films. The void filling of wood with coating material has the strongest impact on the uptake of liquid water. A limited reduction was observed for the equilibrium moisture content, the diffusion coefficient during adsorption and the rate of dimensional change. No influence on the equilibrium swelling have been found but the shrinkage during desorption was however often slightly increased for the wood-coating composites. The limited impact of the penetrated coating on moisture related properties can to a large extent be explained by the low void filling after drying (20–60%) and the relatively high moisture sorption and swelling of the coating film itself. In general, it can be concluded that the moisture protection of penetrated coating material is low in comparison to coating applied as a film on the surface of wood.