Volume 54, Issue 3

Novel methods developed for characterization and identification of wood-inhabiting fungi target molecules of the organisms such as proteins and nucleic acids and use mycelial interaction, mating, antibodies, electrophoretic protein patterns, oligonucleotide primers and DNA sequencing. The article reviews the respective work on the dry rot fungus Serpula lacrymans in the Hamburg institute and also covers the international literature.

The structure of the middle lamella in Pinus thunbergii has been studied by the rapid-freeze deep-etching (RFDE) technique in combination with transmission electron microscopy (TEM). The ultrastructure of the compound middle lamella was studied in the early phases of the development of woody tissue in the cambial and differentiating xylem, before the heavy incrustation with lignin had occurred. Lignified middle lamella in the xylem was studied both directly and after delignification. It was found that the structure of the unlignified middle lamella in the cambium/developing xylem consists of a fine irregular network probably containing pectin and hemicellulose. As a result of lignin incrustation, the middle lamella becomes increasingly dense and the surface structure of the fully lignified middle lamella appeared to be compact and partly covered with globular structures. After delignification of the lignified middle lamella a thin network with a different structure was revealed. This network probably mainly consists of hemicellulose. No microfibrils of the type that occurs in the primary and secondary walls were found in the middle lamella.

The antifungal activity of cadinane skeletal sesquiterpenoids from Taiwania ( Taiwania cryptomerioides Hayata) heartwood is demonstrated. Using spectral analyses, the absolute structures of three main cadinanes, T-cadinol, T-muurolol, and α-cadinol, all isolated from Taiwania with HPLC, were identified. The amount of these cadinanes was also quantified using GC. The results showed that the total amount of cadinanes extracted from heartwood with n -C 6 H 14 was 6.49 mg per kg of wood. This was much more than the essential oils collected by water distillation from leaves (0.04 mg/kg), sapwood (0.36 mg/kg), or heartwood (1.77 mg/kg). Moreover, results obtained from the antifungal assays demonstrated that αcadinol exhibited the highest antifungal index for both Coriolus versicolor and Laetiporus sulphureus , followed by T-cadinol and T-muurolol. As a matter of fact, α-cadinol completely inhibited the growth of C. versicolor and L. sulphureus at the level as low as 100 ppm. Further comparison of the molecular configuration of these cadinanes reveals that cadinane skeletal sesquiterpenoids with an equatorial hydroxyl group at C-9 and a trans configuration at the ring junction, such as the case for α-cadinol, exhibited the strongest antifungal activity.

Three quarters of the western red cedar's heartwood colour is due to a polymeric material easily isolated by methanol extraction. The nature of this polymer has not been fully investigated and published information is contradictory. Our initial examination of the coloured polymer by pyrolysis-gas chromatography, combined with mass spectrometry, indicated that the polymer was guaiacyl in nature and thus similar to softwood lignin. However, analysis by infrared spectroscopy indicated the presence of both lignin and lignan like moieties. To clarify this issue a more detailed analysis was conducted using nuclear magnetic resonance spectroscopy ( 1 H NMR, 31 P NMR, 13 C NMR). Analysis of the spectra and comparison with the spectra of plicatic acid and a product from mild acid treatment of plicatic acid, indicated that the polymeric fraction was derived almost entirely from lignans. During polymer formation, the highly reactive pyrocatechol moiety in the plicatic acid is destroyed, leaving a guaiacyl-like polymer. The reaction mechanism appears to proceed via an ortho -quinone intermediate followed by polymerization.

The influence of botanical species ( Quercus and Castanea sativa ) and geographical origin (Portugal—three different sites, France and North America) on the qualitative and quantitative content of some extractable low molecular weight phenolic compounds was assessed by HPLC. Chestnut wood had the highest total content of low molecular weight phenolic compounds, followed by the Portuguese oaks and the French oaks, whereas the American oak had the lowest content of these compounds. The contents of phenolic acids, phenolic aldehydes, scopoletin and umbelliferone were significantly different among the studied woods. Both the botanical species and the geographical origin affect the content of low molecular weight organic compounds of woods used in Portuguese cooperage. The results also show that the botanical species seem to be more important than the geographical origin to explain the difference in the wood phenolic composition. So, the separation of trees according to their origin is of considerable interest for coopers and winemakers to choose wisely the woods for the ageing of brandies.

A simple phenolic lignin model compound (syringyl alcohol, SA) was subjected to the reaction with a one-electron oxidizing reagent, Mn 3+ (manganese(III) acetate), in a weakly acidic aqueous medium or in acetic acid medium under various oxygen pressure (0 to 1.0 MPa). Yields of the reaction products, especially that of methanol, were used to evaluate the progress of oxidation reaction and the difference of oxidation mechanism due to the presence of molecular oxygen. The difference in the oxygen pressure did not result in any detectable difference in reaction products, suggesting that molecular oxygen did not participate in the oxidation process which were initiated by one-electron abstraction from phenolic hydroxyl group. Contrary to this, a clear effect of oxygen pressure on the methanol yield was observed when methanol was determined after the reaction mixture being subjected to the alkali post-treatment. This is attributed to the generation of some active species from the reaction of Mn 2+ with molecular oxygen and to the simple oxygen-alkali oxidation.

The potential of several tertiary amine catalysts (pyridine, 4-dimethyl-amino pyridine, N-methyl pyrrolidine and N-methyl pyrrolidinone) for the acetylation of Corsican pine sapwood, using acetic anhydride, has been investigated. Rates of reaction were compared with non-catalysed acetylation using acetic anhydride. The hypernucleophile 4-dimethylamino pyridine was found to be the most effective catalyst of those studied. At a concentration of only 1% of the catalyst in acetic anhydride, a weight percent gain of 20% was realised, compared with 7% for the uncatalysed reaction, after 30 minutes system at 100°C. The influence of substrate swelling upon the rate of reaction with wood is discussed.

Effluents from the chlorine dioxide bleaching of chemical pulps were characterized with respect to high and low molecular weight material, COD, TOC, elemental composition, and carboxylic acid and methyl ester content. A technique was developed for the quantitative estimation of muconic acid-type structures as moities of the high molecular weight material. The method is based on the use of quantitative 13 C NMR and the pH-dependent cyclization of muconic acids in aqueous solution. 20–40 % of the carboxylic acids in the high molecular weight material isolated from bleach plant effluents from three softwood kraft mills were found to exhibit muconic acid-type behaviour.

In pulp bleaching, while the peroxide-stage chemical charges and the physical operating conditions have been optimized, little attention has been given to the order in which these chemicals are added. We assessed the effects of chemicals, individually and combined, and the effects of the order of addition of these chemicals on peroxide bleaching performance in an acid-treated pulp and in a chelated pulp. We found that adding magnesium to an acid-treated pulp is essential for good peroxide bleaching, while adding magnesium to a chelated pulp provides only a marginal improvement in most additions. But adding magnesium and sodium hydroxide, or sodium hydroxide and magnesium sequentially into a bleaching solution before adding the solution into pulp, causes inefficient peroxide bleaching. This is particularly the case with a chelated pulp. This inefficiency can be avoided if a chelant is added between the additions of magnesium and sodium hydroxide. Magnesium is substantially more effective when in a complex form with either the pulp or a chelant, and the optimum concentration of magnesium for use in peroxide bleaching can be determined by following the peroxide residual.

A process has been developed for densifying wood by thermo-hydro-mechanical (THM) means. The resulting product is then called THM densified wood. Small specimens of different wood species, with or without knots, were densified in their radial, tangential and transversal directions. Tests on THM densified wood show significant improvement in mechanical properties. THM densified wood is less hygroscopic and more stable, with almost no shape memory. We have shown that the shear strength of wood in its grain direction increases more than tenfold by THM treatment. This article gives testing results and micrographs of THM densified wood, and discusses the physical nature of different mechanisms intervening at the wood cell wall level during the thermo-hydro-mechanical process.

Black-colored heartwood of sugi ( Cryptomeria japonica D. Don) logs with bark attached were smoked, heated, and smoke-heated separately to improve the heartwood color. After each treatment, changes of heartwood color, amounts of extracts (hot water, 1 % sodium hydroxide, and ethanol-toluene), metal ions (sodium, potassium, calcium and magnesium), and pH were examined. In addition, changes of heartwood color by UV irradiation (wavelength at 254 nm and 365 nm) also were studied. Heating and smoke-heating of logs prevented blackening of the heartwood, leading to a yellow-white heartwood color, whereas smoking did not largely change the heartwood color. Almost no differences in the amounts of extracts and metal ions were found in the control and treated woods. Thermal and smoke treatments decreased the pH from the original 8.1 to 6.0 and 7.4, respectively. The results obtained suggest that the changes of pH by both heating and smoking relate to the heartwood color changes in black-colored sugi. In the heated and smoke-heated woods, redness and yellowness were increased by the subsequent UV irradiation at 365 nm, whereas brightness was decreased. Apparently, the heartwood color of black-colored sugi was changed from yellow-white to red by the UV irradiation, the red color being the normal heartwood color of sugi. However, UV irradiation did not cause significant changes in the heartwood color in the control and smoked woods. These results suggest that UV irradiation of the thermally treated wood showing the resulting yellow-white color recovered the redness as found in normal red-colored heartwood, which seems to be caused by chemical changes of pigments under a weak acidic condition in the black-colored heartwood of sugi.

Dubinin's theory of micropore volume filling was used to describe the isotherms of water resorption and desorption by natural wood of twelve species and chemically modified birch wood. The analysis showed that each wood sample is characterized by its own pair of the main equation parameters. The correlation between these parameters was also determined. The resorption/desorption characteristic which is a combination of the main equation parameters of the above mentioned theory was revealed to be invariable for all the studied examples of natural wood. It can be used for estimation of wood substance disturbances caused by chemical modification and probably anthropogenic factors effecting during wood formation. The thermal coefficient as a function of relative vapor pressure was found. This dependence and the main equation of the theory of micropore volume filling can be used to calculate sorption equilibrium for wood/water system under the limited set of experimental data.

Acoustic emission (AE) generated in pine wood samples upon bending across the grain under simultaneous moistening of the tension zone, was measured. The aim of the study was to determine the effect of external tension load on AE generated during asymmetrical moistening of dry wood samples in water. The cumulative counts of AE signals recorded during simultaneous moistening of the tension zone of sample were proportional to the intensity of the mechano-sorptive strain. AE starts when the mechano-sorptive strain in the tension zone (ε T ) reaches a value close to 0.8%.

Experimentally it was observed that the dynamic modulus of elasticity calculated from the velocity of stress wave or ultrasonic wave and the density of wood in green condition increased with increasing moisture content. This statement disagrees with the physical meaning of data observed with static tests, namely the decreasing of all mechanical properties of wood with increasing moisture content. To elucidate this discrepancy a simulation procedure was developed to study the effect of free water, present in wood above the fiber saturation point on wave velocity. For this purpose the coefficient k, related to the mobility of free water was defined, as a ratio of free water vibrating simultaneously with water present in cellular wall (k = 0.6 for stress wave velocity and k = 0.7 for ultrasonic velocity). The simulation procedure using corrected values of velocity and density showed that the elastic moduli are relatively constant above the FSP, as all the mechanical parameters determined with static tests.

The mechanism of longitudinal contraction of Yezo spruce ( Picea jezoensis Carr.) during treatment with aqueous NaOH solution is discussed. The contraction of wood samples increased with an increase in the concentration of NaOH solution and in heating temperature. Measurements of the stress relaxation and the twist angle during the alkali treatment showed that the alkali treatment caused the contractive and twist forces of a tracheid cell wall in longitudinal and tangential directions, depending on the components of contractive force. The temperature dependence of the contraction and the thermodynamics led to the conclusion that the longitudinal contraction of samples is due to that of microfibrils via an entropy-elastic force.

In order to make clear the molecular mechanism of the dielectric relaxation based on adsorbed water in wood cell wall during moisture changing process, the temperature and frequency spectrums of dielectric processes of Sikkim spruce ( Picea spinulosa Griff .) were measured in three different adsorption processes. Three levels of relative humidity used were 40, 80 and 100 %, respectively, and the temperature was kept at 20°C. In oven-dry state, relaxation process I based on the reorientation of CH 2 OH groups in amorphous region of wood cell wall was observed. While in moist state, relaxation process II based on ionic conductivity and relaxation process III based on the additive reorientation of CH 2 OH groups and adsorbed water molecules occurred. Within higher humidity region, relaxation process IV concerned with adsorbed water in lignin was observed in the initial adsorption period, but it vanished with further adsorption.

Processed bamboo culms capable of maintaining the greenish color in their skin have increased economic value. The use of protectors to preserve the green color and to improve the color fastness of bamboo culms has, therefore, attracted great interest in the industry. In this paper three exposure tests, including accelerated UV lightfastness, outdoor weathering, and indoor exposure, were used to evaluate the color fastness of ma bamboo ( Dendrocalamus latiflorus Munro) treated with chromium based reagents. Experimental results revealed that bamboo culms treated with CCP (chromated copper phosphate) or CP (chromated phosphate), both homemade by the authors, exhibited excellent color fastness. Among all inorganic salt-treated bamboo culms the CP-treated samples had the brighter greenish skin and also provided the best green color fastness. It was further noticed that ultraviolet light plays an important role on the color conversion of CrO 3 -treated bamboo. The green color becomes significantly enhanced with increased exposure time.