Volume 55, Issue 4

Lignin content, lignin composition and lignin removal were investigated in hybrid aspen ( Populus sieboldii X Populus gradidentata ) with suppressed peroxidase (POX) contents, involved in the dehydrogenative polymerization of monolignols. No significant suppression of the lignin content of the transgenic hybrid aspen was observed, but one (POX 29) of the POX-suppressed hybrid aspen species had a lower lignin content and gave a higher pulp yield at the same lignin content in kraft pulping than the control wild type. The molecular weight distribution of kraft lignins, sugar compositions and yields of nitrobenzene oxidation products of the transgenic woods were not different from those of the wild-type wood. These results indicate that suppression of POX may hold promise for producing woods suited for milder kraft pulping conditions using less chemicals and lower pulping temperature.

In this paper, we examined the ability of deep and surface staining fungi to utilize wood tissue nutrients. Fungal isolates were inoculated onto fresh billets and γ-sterilised sawnwood, both from Pinus contorta , and also onto defined nutrient media. The wood samples were assessed for host viability, fungal growth and nutrient status. The results indicated that the most aggressive sapstain species on fresh logs was Ceratocystis coerulescens , followed consecutively by Leptographium spp., Ophiostoma minus , O. piliferum , O. piceae , O. setosum , O. pluriannulatum and Aureobasidium pullulans . HPLC analysis of soluble sugars in fungal-infected wood indicated that mannose was the most depleted sugar, followed by glucose. Lipid analysis of infected wood indicated that Leptographium spp. and C. coerulescens greatly reduced the triglyceride fraction and that there was a wide spectrum of consumption of triglyceridederived fatty acids between the fungi. On defined media, the carbon source mannose led to the darkest pigmentation for all tested fungi. For C. coerulescens , the order of pigmentation intensity for the remaining tested carbon sources was reversed when compared to the other fungal species.

Sugi (Japanese cedar, Cryptomeria japonica D. Don) green logs with black heartwood were smoked, heated, and smoke-heated separately to improve the heartwood color. After each treatment, changes in heartwood color, pH, and extract amounts were examined. In addition, changes in heartwood color caused by UV irradiation were observed. Heating and smoke-heating of logs prevented the heartwood from discoloring to black, and the resulting color of thermally-treated heartwoods was yellow-white, whereas smoking alone allowed discoloration to black. The pH value decreased from the original 7.6 to 6.8 by smoking and to 6.5 by thermal treatment. The results obtained here suggest that a pH drop in heartwood by thermal treatment is involved in color changes of black heartwood. When thermally-treated black heartwood was exposed to UV light, redness and yellowness increased and brightness decreased. The resulting color tone was reddish brown. The color of non-thermally-treated woods, however, showed little change. Furthermore, acetone, ethanol, and methanol extracts of thermally-treated black heartwood showed an increase in redness by UV irradiation, but the residues showed little color change. The coloring substances relating to the reddening of heartwood could be extracted with these solvents, particularly with methanol. Reddening in black heartwood by a combination of smoke-heating and UV irradiation is considered to be due to a decrease in brightness and an increase in both redness and yellowness.

In order to reduce the leachability of boron compounds in wood, the double treatment of tetraphenylborate sodium salt [(C 6 H 5 ) 4 BNa] (TPBNa) with potassium chloride (KCl) or tetramethylammonium bromide [(CH 3 ) 4 NBr] (TMABr) was investigated by impregnating them into sapwood specimens of Japanese cedar ( Cryptomeria japonica ) to form insoluble salts of tetraphenylborate tetramethylammonium or tetraphenylborate potassium. The reduction of boron retention in treated wood specimens after the waterleaching test was very small, showing the good fixation of boron compounds in wood. The double treatment of TPBNa salts with TMABr or KCl solution also showed an excellent decay-resisting effect against both Coriolus versicolor and Tyromyces palustris at low boron retention.

In situ polymerization of bioactive monomers was investigated as an alternative to conventional preservative treatments. The results are presented in a series of two papers. In Part 1 of the study, six acrylate monomers with covalently bonded, potentially bioactive moieties were synthesized: (1) pentachlorophenolyl acrylate (PCPA), (2) tributyltin acrylate (TBTA), (3) 8-hydroxyquinolyl acrylate (HQA), (4) 5,7-dibromo-8-hydroxyquinolyl acrylate (DBHQA), (5) diethyl-N 1 N-bis(acryloxyethyl) aminomethyl phosphonate (Fyrol 6 acrylate, F6A), and (6) tetrabromobisphenol A acrylate (TBBPAA). All of these acrylates, except F6A, were purified. Southern pine sapwood samples were treated with acrylate solutions (except TBBPAA) at different retention levels and various amounts of crosslinker (trimethylolpropane trimethacrylate, TMPTM), polymerized in situ , and then acetone leached. The relative amount and location of the polymer in earlywood and latewood of selected samples were determined by scanning electron microscopy and x-ray analysis. Distribution of the compounds varied with treatment. Biological and thermal properties of the treated wood are discussed in Part 2 of this series.

This paper is the second in a two-part series on in situ polymerization of bioactive monomers as an alternative to conventional preservative treatments. In this part of the study, bioactive monomers were evaluated for their ability to provide resistance to decay and protection against fire. Five bioactive monomers were synthesized: (1) pentachlorophenolyl acrylate (PCPA), (2) tributyltin acrylate (TBTA), (3) 8-hydroxyquinolyl acrylate (HQA), (4) 5,7-dibromo-8-hydroxyquinolyl acrylate (DBHQA), and (5) diethyl-N 1 N-bis (acryloxyethyl) aminomethyl phosphonate (Fyrol 6 acrylate, F6A). Southern pine sapwood samples were treated with acrylate solutions at different retention levels and with various amounts of crosslinker (trimethylolpropane trimethacrylate, TMPTM), then polymerized in situ . Methyl methacrylate (MMA) was used as the control. Biological resistance to the brown-rot fungus Gloeophyllum trabeum was determined on acetone-leached and unleached samples. PCPA showed some biological efficacy in the absence of crosslinker, but otherwise provided no more protection than did MMA alone. TBTA was biologically effective at all retention levels except with crosslinker concentration ≥10 %. HQA was biologically effective at ≥ 2% retention. F6A was not biologically effective, although unleached wood treated with 10% F6A and 5% or no crosslinker showed some resistance to decay. The 5% DBHQA plus 5% crosslinker treatment was biologically effective in both leached and unleached wood. The effects of the highest treatment level of each monomer, after polymerization, were also evaluated by thermogravimetric analysis. All treatments provided some resistance to fire. The best treatment was 10 % F6A, which resulted in the lowest mass loss (67.0 %) and the lowest maximum temperature of pyrolysis (308.5 °C).

Transmission electron microscopy (TEM) of the walls of Picea abies axial tracheids showed the distribution of lignin in the S2 layer to be inhomogenous. At relatively low magnifications, some parts of the outer and inner S2 layer appeared more electron dense than the mid region in the tracheids which were in contact with or in proximity to a ray. At similar magnifications, the presence of radial and tangential features was observed in the S2 layer of the tracheids which were in contact with or close to rays as well as in those which occurred elsewhere. Higher magnification views showed the S2 layer to be differentiated into electron lucent and dense regions in both radial and tangential directions. A comparison of the counts made of lignin particles in these regions suggested that the differentiation of the S2 wall into lucent and dense regions resulted from inhomogenous distribution of lignin observable at a nano level.

Lignin distribution was determined by interference microscopy, and by confocal laser scanning microscopy (CLSM) for a range of agricultural residues including coppice poplar, linseed, and wheat straw. Interference microscopy was used to determine the lignin concentration in the middle lamella at the cell corner, and for the secondary wall of libriform fibres in the secondary xylem of poplar and linseed. Wheat was examined in the same way for cortical fibres. In addition the secondary wall of vessel elements was examined for poplar. Confocal microscopy was used to confirm the results from interference microscopy by providing semiquantitative information based on lignin autofluorescence, and by staining with acriflavine. Wheat had the lowest level of lignification, with 31 % lignin in the middle lamella of cortical fibres and 9% lignin in the secondary wall. Poplar had a lignin concentration of 63% in the middle lamella and 6% in the secondary wall of libriform fibres, while linseed had corresponding values of 69 % and 13 %. The secondary wall of poplar vessel elements had a lignin concentration of 25 %. In all three species most of the stem tissue was lignified except for phloem and bark, where present. In linseed the pith was unlignified. In wheat, most of the parenchyma cells were lignified except for a few cells lining the stem cavity. Libriform fibres in poplar and linseed sometimes had an unlignified gelatinous layer in samples containing tension wood. In linseed, lignification was greater in xylem fibres compared to bast fibres. Ray parenchyma cells of poplar and linseed appeared to be lignified to the same extent as xylem fibres.

Milled wood lignins isolated from genetically modified poplar trees were studied by quantitative 31 P NMR spectroscopy, in combination with thioacidolysis and mild alkaline hydrolysis. The genetic transformation of the trees included down regulation of CAD and COMT enzyme activities. These analyses confirmed that moderate CAD down-regulation does not substantially alter lignin structure. In contrast, severe CAD deficiency alters the lignin structure more profoundly by decreasing the syringyl/guaiacyl ratio and increasing the degree of condensation of the lignin. The most severe alterations were observed in the lignins from the COMT-transformed lines.

Three biomimetic systems were evaluated for their selectivity in a model system for pulp. FeSO 4 , Fe-EDTA and hemoglobin, in the presence of H 2 O 2 , constituted the biomimetic systems. Sodium lignosulfonate and hydroxyethyl cellulose (HEC) were used as a model system to represent lignin and carbohydrate fractions in pulp. A simple kinetic model was used to determine kinetic parameters for depolymerization of each substrate. Point selectivities at two different H 2 O 2 concentrations were evaluated on the basis of the resulting expressions. Hemoglobin demonstrated superior selectivity for lignosulfonate degradation at a high H 2 O 2 level. The production of hydroxyl radicals from each of the biomimetic systems was measured using a chemiluminescence assay. For the FeSO 4 and Fe-EDTA systems, depolymerization was related to the amount of radicals generated. The fate of reacted H 2 O 2 was evaluated using a specially designed reactor to measure H 2 O 2 consumed by reaction and that decomposed. To achieve a given number of chain scission in lignosulfonate, the hemoglobin system consumed the least amount of H 2 O 2 .

Investigations were conducted on the oxidative ammonolysis of REPAP organosolv lignin at 130 °C in 0.8M NH 4 OH solution under oxygen pressure of 12 bar. The lignin was completely solubilized at the reaction time of 165 min. The kinetics of the nitrogen incorporation consists of two phases. The first phase is up to the reaction time of approximately 35 min including 15 min heating up period. The rate of nitrogen incorporation in the first phase is 2.3 times higher than that in the second phase: κ 1 = 4.58 × 10 −4 s −1 versus κ 2 = 1.90 × 10 −4 s −1 . The oxygen uptake and CO 2 formation in the reaction is rather high. When the nitrogen incorporation was ceased after reaction for 255 minutes, more than 4 moles of oxygen/C 9 -unit of lignin were consumed and approximately 1.5 moles of carbon dioxide/C 9 -unit of lignin were released. In addition, extensive O -demethylation of methoxyl groups occurred. The molar ratio of the nitrogen incorporation to the methoxyl group eliminated is approximately 1.4 and 0.7 for the soluble and insoluble N -modified lignins, respectively. Structural analyses of the soluble N -modified lignins by FTIR and 1 H NMR spectroscopic techniques showed only quantitative differences in the spectra obtained at different reaction times. This indicates that the reaction pathways do not change in the course of the oxidative ammonolysis. Possible reaction mechanisms of the oxidative ammonolysis are discussed on the basis of the experimental data.

Investigations were conducted on the effects of oxygen pressure on the oxidative ammonolysis of REPAP organosolv lignin at 130 °C under oxygen pressure of 5, 8 and 12 bar. The rates of reactions monitored, such as nitrogen incorporation, lignin solubilization, oxygen uptake and CO 2 formation, increase with increasing oxygen pressure. Kinetics of nitrogen incorporation under different oxygen pressure consists of two phases and follows a first order law in each phase. Linear correlation between the rate of nitrogen incorporation and oxygen pressure implies that the reaction is first order with respect to oxygen concentration. This indicates that oxygen participates directly in the rate-determining step of nitrogen incorporation. The rate of lignin solubilization also linearly increases with increasing oxygen pressure, implying that the rate of lignin degradation directly depends on oxygen pressure. The nitrogen incorporation is linearly correlated with the oxygen uptake, CO 2 formation, oxygen incorporation into lignin, loss of carbon and methoxyl group content under all values of oxygen pressure and during the entire reaction period. This suggests that the reactions in the oxidative ammonolysis of lignin proceed via the same pathways in the different kinetic phases. In addition, the changes in the oxygen pressure were found to have only minor effect upon the coefficients of these linear correlations. This is in good agreement with the structures of N -modified lignin elucidated from FTIR and indicates that oxygen pressure affects only the reaction rate, but not the reaction mechanism.

The water and α-pinene released during sawdust and flake drying were simultaneously measured. For sawdust, the drying profiles for water and pinene are very different at oven temperatures of 105 °C, but are similar at 200 °C. There is an initial burst of pinene very early in the process, which is mainly attributed to the loss of pinene dissolved in surface water. Later, the pinene and water are released in a nearconstant ratio, which is ascribed to water mobilizing pinene from the interior of the wood matrix to the wet line. The surfactants present in wood are believed to solubilize pinene into water. Finally, pinene is lost through evaporation when the wood is almost dry. Hence, at least three mechanisms are operative for the movement and release of α-pinene and other terpenes from 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. In this second part, the method of homogenisation is used to capture the contrast of property between the gaseous phase and the solid phase. Homogenisation problems are computed using a Control Volume formulation. The tracheid model developed in Part 1 has been used to define several elementary representative volumes. Consequently, bound water diffusivity and thermal conductivity can be predicted for each material direction as a function of local wood density. For practical applications, analytical models fitted from the computed values allow these property variations to be easily and accurately determined.

Optimization with distributed computing is performed on a two-dimensional orthotropic drying model which allows boards with arbitrary outtake of the log and sapwood/heartwood distribution in the cross section. Drying schedules with an optimized variation of temperature and humidity which yields minimized drying time are created at the same time as moisture, stress and deformation levels are considered. A numerical example with distributed computing of a board with a mixture of sapwood and heartwood is presented. Drying starts from the fibre saturation point.

Using four different wood species, the wetting behaviour of sanded wood surfaces was compared with that of microtomed surfaces. Sanding caused lower contact angles and lower total surface free energies. Electron donor components were considered to be responsible for the observed changes according to the applied acid-base approach. The time behaviour of sanded surfaces differed from the microtomed reference, insofar as the volume of a deposited drop of water decreased very rapidly as soon as it was applied, indicating fast penetration into the wood. A qualitative analysis by SEM revealed a heavily torn upper-most cell layer on sanded surfaces, which was assumed to be responsible for the increased surface free energy and enhanced penetration.

Diffusion tests were made in wood chips of northern pine ( Pinus sylvestris ), birch ( Betula verrucosa ) and spruce ( Picea abies ). The chips were pre-treated in two different ways, immersion into water and by steaming. The new results covering very high concentrations, 0.5 mol/dm 3 up to 1.5 mol/dm 3 , of NaCl, NaOH and Na 2 S were recorded for both ways of pre-treating samples. The results were graphically compared, with the main emphasis on the differences between the immersed and the steamed samples. The differences were shown to be not only in the magnitude of the flow; clear differences in the concentration dependencies were also noticed. Spruce was more affected by the pre-steaming than pine and birch.