Volume 55, Issue 3

Rot fungi Fomitopsis pinicola and Sterum hirsutum were employed in preparing decayed birch wood samples. The degree of decay was determined as weight loss. The samples were analysed by analytical pyrolysis (PY) and infrared spectroscopy (FTIR) and correlated to weight loss by means of multivariate calibration. The above techniques provided both quantitative assessments and qualitative interpretations. The PY technique can distinguish between the fungi at all degrees of decay while FTIR failed at low weight losses. This may be due to fungal biomass, the amount of which is difficult to determine in the decayed sample. Both analytical techniques can be calibrated to predict weight losses from 0 to 45%. Different fungal degradation patterns could also be identified, especially when pyrolysis was used. F. pinicola degraded lignin to a lesser extent at the same weight loss than did S. hirsutum . General degradation mechanisms could be confirmed for the fungi studied.

Previous work by Srinivasan et al. (1992) and Bruce et al. (1996) has shown that inhibition of wood decay fungi by volatile organic compounds produced by Trichoderma spp. is dependent on the type of growth media and age of the Trichoderma colony. Wheatley et al. (1997) identified five volatile organic compounds produced by Trichoderma spp. that may be inhibitory to wood decay fungi. The effects of four of these compounds (Acetone, 2-methyl-1-butanol, heptanal and octanal) were tested over a range of concentrations against four selected wood decay fungi. Fungi were incubated in malt extract broth under appropriate conditions and growth was estimated by biomass production and respiration rates. Growth of all four fungi was affected by at least one of the compounds, usually by inhibition but occasionally stimulation. All but two of the fungus/chemical combinations showed significant effects on biomass development ( P < 0.05) and fifteen of the sixteen combinations produced a significant concentration effect on respiration rates ( P < 0.05). The aldehydes, heptanal and octanal, were very effective against all four wood decay fungi. All four fungi were inhibited by more than 80% at 25 μg ml −1 by heptanal and three of the four fungi were totally inhibited at 250 μg ml −1 . Acetone did not inhibit the four wood decay fungi and even stimulated fungal growth at some concentrations. 2-methyl-1-butanol was only effective at the highest concentration of 2500 μg ml −1 . The implications of these results for the biological control of wood decay fungi and future studies are discussed.

Phlebiopsis gigantea , a white-rot fungus currently being tested in biological processing applications for the pulp and paper industry, was shown to effectively inhibit blue stain fungi in both laboratory and field trials. Inoculation of logs with P. gigantea shortly after cutting resulted in up to 86% colonization of logs in the laboratory and 100% in field studies. Colonization of logs by blue stain fungi such as Ophiostoma piliferum and O. piceae was greatly reduced or completely inhibited with prior inoculation by P. gigantea . In field studies, blue stain fungi colonized up to 53% of the sapwood and stained as much as 31% of the sapwood in non-inoculated control logs in contrast to 4% colonization and 2% stain in treated logs. Logs inoculated with O. piliferum 2 weeks prior to inoculation with P. gigantea were 88% colonized by O. piliferum and had 33% of the sapwood stained after 7 weeks, and 33% colonized and 18% stained after 29 weeks. Scanning electron micrographs of P. gigantea and O. piliferum hyphae showed P. gigantea parasitizing the blue stain fungus. Phlebiopsis gigantea was shown penetrating and growing adjacent to collapsed and disintegrated blue stain hyphae. Phlebiopsis gigantea also decolorized sapwood previously stained blue.

Information on the natural decay resistance and efficacy of CCA-treated rubberwood is important for the development rubberwood industry. The purpose of this study was to determine the natural decay resistance of rubberwood and the efficacy of CCA-pressure treatment in order to explore a new opportunity for this abundant raw material. Natural decay resistance and efficacy of CCA was estimated using soil-block test according to AWPA E10-91. Cubes were exposed to six wood-decay fungi: two each from white, brown, and soft rot. The moisture content of test cubes exposed to Irpex lacteus and Trametes versicolor increased with weight loss increase, while that exposed to Gloeophyllum trabeum and Postia placenta decreased. After a 12-week incubation period the average weight loss by white rot and brown rot fungi was about 1.5 times higher than that of soft rot fungi. CCA retention of 4.1 kg/m 3 reduced weight loss to between 8% and 10%, retention of 14.5 kg/m 3 protected weight loss by all test fungi from exceeding 2%.

The lightfastness of butyrylated China fir ( Cunninghamia lanceolata var. lanceolata ) and maple ( Acer sp.) was evaluated in this study, and its effectiveness was compared with that of acetylated specimens. The color fading in acetylated China fir and maple woods was reduced to half that of untreated specimens, after a 24-day UV lightfastness test. The effectiveness of butyrylation on photodiscoloration prevention in wood was even more pronounced than that with acetylation. With an 18.57% weight percent gain, butyrylation remarkably inhibited the discoloration of wood following UV irradiation. Based on infrared spectral analysis, the lignin of both untreated and butyrylated woods deteriorated after exposure to UV light, but the holocellulose in butyrylated wood was more resistant to the UV light. Furthermore, results obtained from diffuse reflectance UV-VIS spectral analysis elucidated that the absorption of irradiated butyrylated wood, in comparison with that of the irradiated but untreated specimens, was lower in both UV light and visible light regions. It also revealed that the inhibition of photodiscoloration of wood by butyrylation was caused mainly by a significant reduction of chromophoric derivatives, such as quinoid compounds, formed on the wood surface.

The chemical composition of lipophilic extractives in paper pulps from Eucalyptus globulus wood during kraft cooking followed by TCF (“totally chlorine free”) and ECF (“elemental chlorine free”) bleaching sequences has been determined by gas chromatography and gas chromatography-mass spectrometry. The chemical analyses revealed that the composition of the lipophilic extractives in pulp after kraft cooking and TCF bleaching with hydrogen peroxide was similar to that of E. globulus wood extractives, sitosterol and sitosterol esters being the predominant compounds. In contrast, the presence of these compounds was almost negligible in pulp after ECF bleaching with chlorine dioxide and only the saturated sterol stigmastanol, in both free and esterified forms, survived the bleaching.

FTIR spectroscopy was used to estimate monosaccharide content in Eucalyptus globulus wood, using the natural variability of the species for calibration and validation of the method . A total of 38 samples from 9 year old trees from provenance trials was used. The composition ranged for glucose from 43.2% to 59.5%, for xylose from 9.4% to 17.8%, for galactose from 0.5% to 5.4%, for mannose from 0% to 2.8%, and for rhamnose from 0.3% to 0.8%, based on extractive-free dry wood. The multivariate analysis gave in general, better results with increased R 2 , lower SEC and SEP errors, although the univariate method also gave good fits with high coefficient of determination (R 2 ) based on remaining data once outliers were removed. FTIR techniques may be used in large scale breeding programmes to measure wood monosaccharide composition with considerably less effort and in shorter time than wet-lab methods, once a reliable calibration has been made for the species.

Sapwood of Scots pine ( Pinus silvestris L.) was acetylated with 14 C- and 3 H-labelled acetic anhydride. The distribution of acetyl groups was investigated with microautoradiography and microautoradiographs were evaluated with ESEM, Environmental Scanning Electron Microscopy. The investigation showed that the impregnation of wood with radioisotope-labelled substances provides a good opportunity to investigate the location of substances covalently bonded to the wood material. Introduced 14 C-labelled acetyl groups show an even distribution in the wood cell wall, with no discernible concentration gradients at acetylation levels of about 5, 15 and 20% weight gain. 3 H-labelled acetyl groups show an even distribution in the wood cell wall at 15 and 20% weight gain, with no discernible concentration gradients. At the 5% weight gain level, however, an uneven distribution of 3 H-labelled acetyl groups over the cell wall is observed. Nevertheless, the unevenness is random and no concentration gradient is discernible at this level. 3 H with a relatively high resolution, 0.5–1 μm, compared to 14 C with a resolution of 2–5 μm, gives more accurate information about where exactly the acetyl groups are situated in the wood cell wall. Acetic anhydride was evenly distributed when a full impregnation procedure was used. The chemical and physical properties of acetic anhydride allow a uniform penetration into the pine cell wall and a complete acetylation takes place when the specimens are heated.

Photoyellowing of lignocellulosic materials has been studied with a new technique based on solid state 13 C-NMR analysis of 13 C-enriched DHP in cell wall tissue. The selectively 13 C-enriched cell wall-dehydrogenation polymer (CW-DHP) was prepared directly on differentiating xylem from spruce ( Picea abies ) at pH 6.0 by administering β- 13 C-enriched coniferin in an enzymatic system consisting of glucose oxidase, β-glucosidase, and the naturally occurring water-insoluble enzymes remaining in the cell wall. The bonding pattern of the formed CW-DHP was found to be: 42% β-β, β-5, and β-1 substructures; 36% β-O-4 derived substructures; and 22% coniferyl alcohol and coniferaldehyde end-groups. The 13 C-NMR analysis of unirradiated and irradiated tissue revealed a decrease in the relative amount of coniferaldehyde and/or coniferyl alcohol end-groups during irradiation. Prolonged irradiation also introduced new signals centered at 37, 70, and 102 ppm. The results indicate that the present technique, with the formation of DHP in a naturally lignifying carbohydrate environment, has the potential of being a valuable tool for the study of structural changes of lignin during light-induced yellowing.

The amount of carbonyl groups in an organosolv lignin was determined by 19 F NMR spectroscopy after different derivatizations: derivatization with trifluoromethylphenylhydrazine, fluorobenzoylation of alcohol groups formed after NaBH 4 reduction of lignin, fluorobenzoylation of phenolic hydroxyl groups after catalytic hydrogenation of lignin. Oximation was also used for comparison. Carbonyl group contents determined by 19 F NMR after trifluoromethylphenylhydrazine derivatization were in good correlation with results from other methods. Trifluoromethylphenylhydrazine derivatization is a fast and easy technique, which provides a distinct quantification of aldehyde, ketone and quinone groups. Some round robin lignins (Milne et al. 1992), using trifluoromethylphenylhydrazine derivatization and modified oximation (Zakis 1994) provided significantly higher carbonyl group contents than the round robin test data, which had been measured either by classical oximation or by reduction-UV methods. Other recently reported carbonyl group estimations on round robin lignins (Faix et al. 1998; Ahvazi et al. 1999) were either in agreement or in disagreement with the herein-presented results. This indicates that carbonyl group analysis in lignins is difficult and that care must be taken when selecting an appropriate method.

The reactions of the β-aryl ether lignin model 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-propanol on heating in aqueous solution have been studied. Guaiacol, isoeugenol, vanillin, 1-(4-hydroxy-3-methoxyphenyl)-1-ethanol, 1,2-bis(4-hydroxy-3-methoxyphenyl)-1-propanol, 2-(4-hydroxy-3-methoxyphenyl)-7-methoxy-3-methyl-2,3-dihydrobenzo[ b ]furan, dehydrodiisoeugenol and trans -1,2-dihydrodehydroguaiaretic acid were detected in the reaction mixtures. The formation of the products can be envisioned to proceed via homolysis of an intermediate quinone methide. When 2,6-dimethoxyphenol was present in the reaction mixtures large amounts of 1-(4-hydroxy-3,5-dimethoxyphenyl)-2-(4-hydroxy-3-methoxyphenyl)-1-propanol were formed and the yields of guaiacol and isoeugenol were comparatively high. The reaction product pattern can be explained by the occurrence of radical-exchange reactions. The presence of wood meal in the reaction mixtures resulted in an increase in the yield of isoeugenol and a lowering of the yield of dehydrodiisoeugenol. The changes in yields in this case can also be explained by radical-exchange reactions. The significance of homolytic cleavage of β-aryl ether linkages in connection with the technical processing of wood is discussed.

Structural analysis was conducted on residual lignin from pine Kraft AQ pulp, Eucalyptus Kraft lignin from Eucalyptus globulus and Repap Organosolv lignin by 2D 13 C- 1 H correlation NMR spectroscopic techniques such as HMQC sequence. These lignins contain a rather wide variety of saturated aliphatic groups. The HMQC NMR spectra of the lignins do not verify the presence of diarylmethane moieties in any lignin investigated. The type and amount of other condensed structures depend on the nature of lignin preparation. All the lignins investigated still contained β- O -4′, pino- and syringayresinol (β-β′) and phenylcoumarane (β-5′) structures. Stilbene structures were also identified. Vinyl ether structures were present only in Eucalyptus Kraft lignin. All the lignins contain α-carbonyl groups conjugated to aromatic moieties as terminal side chains rather than involving β- O -4′ structures. No coniferyl alcohol and coniferyl aldehyde type structures are detected in the lignins after pulping. The spectra of kraft lignins show some new signals, the origin of which is discussed.

The radial and tangential deformations in a single growth ring of Norway spruce, which was subjected to moderate tensile loading in its radial direction, were measured by use of digital speckle photography. From the measured displacement field, the transverse coefficients of elasticity E R , E T , G RT and ν TR were determined with respect to radial position in the growth ring. As a result of the abrupt change in stiffness from latewood to earlywood in the growth ring, it was possible to establish all four coefficients solely from the radial tension test. The elastic modulus E T was found to be a factor 15 larger in latewood than in earlywood, whereas the corresponding variation for E R was merely a factor 3. The measured variations were in reasonable agreement with predictions from simple two-dimensional honeycomb models of the growth ring cellular structure. The average elastic moduli of the growth ring were found to be twice as large as E R and E T measured in conventional tests on macroscale specimens, whereas the reverse was true for the shear modulus. An explanation to these differences is sought by analysing the loading conditions and deformation behaviour of macroscale specimens used in transverse stiffness testing of wood.

In this work, the extensive knowledge of wood gained at the Ecole Nationale du Génie Rural des Eaux et Forêts by using a combination of microscopic observation and experimental work is being used to postulate material property correlations for a macroscopic heterogeneous “Cerne” growth ring model of softwood. Mathematical tools such as image analysis and homogenisation are used to develop models that capture the effect of the density variation within the wood sample of important macroscopic physical parameters. This first part is devoted to mass transfer in wood due to Darcy's law. Capillary pressure correlations as a function of local density are deduced from image analysis. Thereafter, a tracheid model is proposed for softwood. Its shape evolves from earlywood to latewood according to anatomical observations. Liquid and gaseous permeability values are calculated from this model according to Poiseuille's flow within cells and assuming a linear flow-pressure loss relationship through the pits.