Volume 58, Issue 3

The Bremen Cog is a big ship built AD 1380 from oak wood. After its recovery from the river Weser, the water-logged ship's timbers were successfully stabilized using a novel two-step polyethylene glycol (PEG) treatment. An electron microscopic study of the patterns of degradation and of the distribution of PEG within the Cog wood is described. Descriptions like these do not exist for many well known archaeological objects. SEM revealed that in areas with extensive degradation, wood cell walls are thinned and cells have a distorted appearance. TEM provided evidence that the wood has been degraded primarily by erosion bacteria. The stabilization treatment involved impregnation first with PEG 200 and then with PEG 3000. The SEM observations of PEG-impregnated wood revealed that in degraded tissues all cell types are well filled with PEG 3000. Non-degraded tissues are impermeable to PEG 3000 and are impregnated only with PEG 200. SEM confirmed earlier fluorescence microscopic evidence, that PEG 200 is absorbed by the cell walls.

Iodine staining has been used to study the orientation of cellulose microfibrils in wood using light microscopy. The aim of this work was to understand the exact nature of the staining reaction with iodine and to provide insight into the properties and organisation of the wood cell wall. Based on transmission electron microscopy it is apparent that precipitation of the iodine following treatment with nitric acid results in the formation of crystal cavities within the cell wall, which follow the orientation of the cellulose microfibrils. There is no evidence that iodine precipitates within “drying checks” as previously speculated. High resolution confocal reflectance microscopy of crystal cavity orientation indicates that the microfibril arrangement within pit borders can be both spiral and circular. Crystal cavities are much more abundant within the S1 layer than elsewhere. All of the cells examined had crystal cavities in the S1 region, which may be related to the reduced lignification at the S1/S2 boundary resulting in greater porosity of the cell wall at this location. Within the S2 region, clusters of crystal cavities are randomly distributed and occur in widely varying numbers among adjacent cell walls, suggesting variations in the porosity of the S2 wall within and among adjacent tracheids. Cavities form preferentially within more electron lucent regions of the cell wall. The random nature of crystal cavity formation within S2 clusters probably reflects the underlying random nature of the cell wall nanostructure. We conclude that iodine staining can provide important clues to the nanostructural properties of tracheid cell walls.

The aim of the study was to evaluate the effect of refining on the ultrastructure of spruce pulp fibres. Pulps with different molar masses of cellulose (estimated as intrinsic viscosity) were studied after PFI-refining. The molar masses of the polymers were decreased by increases in alkali concentration during pulping. Fibre surface structures were examined using Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM) was used to observe changes in the internal structure of the fibres. Pulps with lower (125 and 329 ml g −1 ) intrinsic viscosity showed more damaged during refining than pulps with higher (620 and 1120 ml g −1 ) intrinsic viscosity. Observations showed pulps with lower intrinsic viscosity to have large decreases in fibre length after refining. Fibres with low intrinsic viscosity (i.e., 125 ml g −1 ) had less primary wall and S1 layer remaining and the external fibrillation and damage of the S2 layer had increased. The S2 wall of fibres with high intrinsic viscosity showed characteristic delamination. Similar delamination was not visible for fibres with low intrinsic viscosity.

The effect of refining on the fiber wall was studied for bleached kraft pulp fractions from pine first thinnings and pine sawmill chips. Hydrocyclone fractionation of both pulps produced fractions enriched in earlywood and latewood fibers. Some external fibrillation but no changes in fiber wall thickness were observed for the thin-walled earlywood fibers during refining. Refining the thick-walled latewood fibers led to extensive external fibrillation and a decrease in fiber wall thickness. The pore structure of the fiber wall opened up during refining for all pulp fractions. Earlywood fibers were more porous than latewood fibers, and fibers from first thinnings more porous than those from sawmill chips. The earlywood fibers from first thinnings had more large pores than the other fiber fractions. In the region of the smaller pores, the pore volume did not change significantly with refining, whereas in the region of the larger pores it increased markedly. In all the fractions investigated, specific hydrolytic enzymes hydrolyzed cellulose more easily after refining. This is an indication of an increase in cellulose surface area and/or disordering of cellulose as a result of refining, probably due to local disorder of the cellulose in the fibril aggregates. Bonding developed most strongly for the earlywood fiber fraction from first thinnings. This is concluded to be due to a combination of fiber dimensions and fiber wall porosity.

The determination of microfibril angle (MFA), cellulose crystallite width and microdensity by SilviScan-2 at CSIRO confirmed that several dark bands in the heartwood of an Acacia species were associated with tension wood (TW) fibres. The straight log was taken from a tree of about 30 years of age that had been apparently growing vertically as there were no signs of the usual stimuli for TW formation. The continuous dark bands of about 5 mm width extended radially from the inner heartwood in a spiral pattern and were separated by continuous normal wood bands of similar width. The TW bands continued in the sapwood from the heartwood boundary to the cambium but were not coloured. The dark colour of the TW was probably caused by extractives being polymerised at the heartwood boundary by enzymes in the TW fibres in the sapwood. The MFA and cellulose crystallite width indicated the TW in a band was of similar intensity throughout its length, indicating similar microstructural characteristics at different cambial ages. The initiation of spiral grain formation occurs before that of tension wood in the Acacia samples studied.

Spruce and beech wood specimens were sanded with four different grain sizes. Surface morphological and chemical changes were determined by roughness measurement, surface free energy determination according to acid-base theory and X-ray photoelectron spectroscopy. An analysis model was proposed to describe chemical changes due to sanding and the data were analysed according to it. It could be shown that spruce and beech behave similarly over a wide range and that chemical changes are non-linear functions of grain size and thus surface roughness. A maximum of surface free energy and a maximum of carbon C1s sub-peak ratio (ratio of carbon bonded to a single non-carbonyl oxygen to carbon bonded only to hydrogen or other carbon atoms) was found for middle grain size.

The visible and near infrared (NIR) (500–2400 nm) spectra and mechanical properties of almost 1000 small clearwood samples from six softwood species: Pinus taeda L. (loblolly pine), Pinus palustris , Mill. (longleaf pine), Pinus elliottii Engelm. (slash pine), Pinus echinata Mill. (shortleaf pine), Pinus ponderosa Dougl. ex Laws (ponderosa pine), and Pseudotsuga menziesii (Mirb.) Franco (Douglas fir) were measured. Projection to Latent Structures (PLS) modeling showed that the NIR spectra of these softwoods could be used to predict the mechanical properties of the clear-wood samples. The correlation coefficients for most of these models were greater than 0.80. All six softwood species were combined into one data set and a PLS model was constructed that effectively predicted the strength properties of any of the individual softwoods. Reducing the spectral range to between 650 and 1050 nm only causes a slight decrease in the quality of the models. Using this narrow spectral range enables the use of smaller, faster, lighter, less expensive spectrometers that could be used either in the field or for process control applications.

To better understand mechano-sorptive creep, creep behaviors were compared in wood samples during the drying process, immediately after drying, and after a long conditioning under constant humidity and temperature. Creep was greater in the sample tested immediately after drying than in the sample conditioned for a long time under relative humidity equal to that after drying, despite the fact that these samples had almost the same moisture content (MC). While the wood that has been moisture-conditioned for a long time is in a stable state, the wood tested immediately after the drying is presumed to be in an unstable state. Moreover, creep of the sample tested during the drying process was greater than that of the sample tested immediately after the drying. It has also been found that the instability decreased with time, indicating that stabilization and destabilization occur simultaneously during the drying process. In recent studies, a decrease in the elastic modulus and an increase in the fluidity of wood immediately after a change in MC or temperature have been reported. These findings are attributed to the instability caused by changes in MC or temperature. Based on the results of the present study and recent studies, we consider the increase in the fluidity of wood as the MC changes to be attributable to instability.

The paper describes a three-dimensional model with non-constant coefficients for the heat and mass transport process in desorption of water in wood. The model is based on conservation of mass and energy and uses various parameters obtained by comparing experimental data with numerical results. In this way, the relations between some parameters and average temperature and moisture content are obtained in the form of analytical expressions. Experimental results obtained for temperature profiles during drying of oak wood samples are compared with the model results. Satisfactory agreement is obtained over a range of drying air temperatures and velocities.

The fractal-geometry approach was used to calculate the thermodynamic properties of moisture sorption by wood from the adsorption isotherms in this study. The results were compared with those from an isosteric approach and a calorimetric approach. The adsorption isotherms of Southern yellow pine ( Pinus spp.) were measured at 4, 15, 30, and 40°C to provide source data for the calculation of both fractal-geometry and isosteric approaches. The results show that the fractal dimensions of the internal surfaces of wood vary between 2.4 and 2.5. The curves of the differential heat of adsorption −∆ H against moisture content from the fractal-geometry approach are similar to those from calorimetric measurements in previous research. The −∆ H values from the isosteric approach increased with moisture content within a moisture content range up to 3%. And, at moisture contents higher than 3%, the −∆ H values from this method are much higher than those from the fractal-geometry approach and calorimetric approach. As a result, the fractal-geometry approach is applicable to calculate the differential thermodynamic properties of moisture sorption by wood in future research.

Wood products with anti-electrostatic properties have wide applications in many fields. However, wood is an insulator and does not itself have anti-electrostatic ability. This study investigated several ionic liquids as anti-electrostatic agents for wood. Ionic liquids are liquids at room temperature (or close to room temperature), possess no vapor pressure and are excellent conductors for electric current. Maple and pine veneers were either soaked in or brushed with five ionic liquids: 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-ethyl-3-methylimidazolium hexafluorophosphate. The ionic liquid-treated wood specimens were then measured for surface resistivity and volume resistivity in accordance with ASTM standards. The effects of application method (brushed vs. soaked) and storage time were investigated. All the ionic liquids studied were effective anti-electrostatic agents for pine and maple. For all ionic liquids tested, pine had lower resistivity, and thus higher anti-electrostatic ability, than maple.

In this study ionic liquids (3-alkoxymethyl-1-methylimidazolium tetrafluoroborates and hexafluoro-phosphates) are successfully used for wood preservation. These liquids are new biocides as well as new solvents which penetrate wood well. The prepared ionic liquids with an alkoxymethyl substituent, which consisted of 7, 8 or 9 carbon atoms, exhibited fungicidal activity against Coniophora puteana (Schum.: Fr.) Karst., Trametes versicolor (L.: Fr.) Pilát and Sclerophoma pityophila (Corda) v. Höhn. The effective and lethal doses were measured by the agar-plate method. In their activity against wood degrading fungi, ionic liquids such as 1-methyl-3-octyloxy-methylimidazolium and 1-methyl-3-nonyloxymethylimidazolium tetrafluoroborates were comparable with commercially available benzalkonium chloride and didecyldimethylammonium chloride. Ionic liquids both with and without DDAC penetrated into Scots pine wood very well.

Bis-quaternary ammonium and bis-imidazolium chlorides, the compounds containing in their structure two symmetrical quaternary nitrogen atoms, were prepared and tested on wood destroying and sapstaining fungi. The effect of the position of quaternary nitrogen atoms upon fungicidal and surface properties was analysed. The antifungal activity of new bis-quaternary ammonium and bis-imidazolium chlorides against Coniophora puteana (Schum.:Fr.)Kr., Trametes versicolor (L.:Fr.)Pilát and Aspergillus niger van Tieghem was much more pronounced than that of quaternary ammonium chlorides. The results confirm the correlation between surface activity and fungicidal activity. The adsorption of bisimidazolium chloride onto pine wood was influenced by pH of applied solutions and the initial solution concentration. With increasing pH of ammonium solution, the adsorption was much greater than in neutral or acidic solutions. Cation structure of the quaternary ammonium chloride exerted a strong influence on quantity of wood-adsorbed chemicals and resistance to water leaching.

The brown-rot fungus Serpula lacrymans MAFF 420003 was grown in a liquid culture medium containing 0.5% carboxymethyl cellulose (CMC) and 1% glucose as carbon sources. Although little extracellular cellulase was secreted, the fungus produced an oxidized quinone-type chelator, 2,5-dimethoxy-1,4-benzoquinone (2,5-DMBQ). The concentration of 2,5-DMBQ in the medium reached a maximum of 90 μmm after a month of cultivation. S. lacrymans could reduce 2,5-DMBQ to 2,5-dimethoxyhydroquinone (2,5-DMHQ), thus a biological Fenton reaction was adopted by the fungus. The changes in the molecular weight distribution of CMC and arabinogalactan were analyzed after the addition of 2,5-DMHQ and Fe 3+ . CMC was apparently depolymerized by the reaction, but the same reaction conditions showed no significant effect on arabinogalactan. These differences suggest the specificities of the biological Fenton reaction via 2,5-DMBQ toward soluble polysaccharides. In addition, the crystallinity index of α-cellulose did not decrease as a result of the reaction with 2,5-DMHQ and Fe 3+ . These results provide indirect evidence that S. lacrymans employs a biological Fenton reaction mediated by a quinone-type chelator, and preferentially degrades amorphous regions of cellulose rather than crystalline regions in the non-enzymatic cellulose degradation.

Resistance of wood reacted in situ with phosphorus pentoxide-amine to the brown-rot fungus Gloeophyllum trabeum and white-rot fungus Trametes versicolor was examined. Wood reacted with either octyl, tribromo, or nitro derivatives were more resistant to both fungi. Threshold retention values of phosphoramide-reacted wood to white-rot fungus T. versicolor ranged from 2.9 to 13.3 mmol, while these for brown-rot fungus G. trabeum ranged from 8.1 to 19.2 mmol. Wood reacted with phosphoramide tested to be more resistant to white-rot than brown-rot attack.

Corsican pine ( Pinus nigra ) sapwood was treated with methanolic solutions of two organo alkoxysilanes ([γ-(methacryloxy)propylx] trimethoxy silane (TMPS), or vinyl trimethoxy silane (VTMS)). Various treatment parameters were studied in order to determine the optimum method for obtaining a stable weight percentage gain. For TMPS, it was found that best results were obtained when a free-radical initiator was used in conjunction with the silane. This indicates that polymerisation of this species occurs via the pendant methacryloxy moeity, a result confirmed by solid-state nuclear magnetic resonance studies of the treated wood. For VTMS, wood moisture content had a profound influence upon the weight percentage gain due to treatment, with higher weight percentage gains obtained as wood moisture content was increased. This indicates that polymerisation in this case occurred via the formation of silanol groups to form siloxane linkages. Solid-state NMR confirmed that the double bond of the organo-functional group was intact after polymerisation had occurred. Modified wood samples were then prepared using optimised treatments for each silane. The wood was prepared to a variety of weight percentage gains and the effect of treatment on the dimensional stability and decay properties of the treated material studied. Treatment of Corsican pine sapwood with the two organo-alkoxy silanes, resulted in only moderate increases in dimensional stabilisation, with anti shrink efficiency values (after 5 water-soak/oven-dry cycles) no greater than 40%. Treatments were found to be relatively stable to hydrolysis. Some differences were observed in the effectiveness of the two silanes in providing protection. Full decay protection required high treatment levels with the silanes.