Miha Humar

Use of wax emulsions for improvement of wood durability and sorption properties

Waxes are used for treatment of wood surfaces for several decades predominately as surface treatments because they weakly penetrate into the wood. In order to overcome this issue, water emulsions were applied in the present experiment. Five water emulsions of various concentrations were used, namely montan wax, polyethylene, ethylene copolymer and oxidized polyethylene wax. Performance of wax treated beech (Fagus sylvatica) and Norway spruce (Picea abies) against white rot, brown rot and blue stain fungi was tested. In parallel, sorption properties of wax treated wood were determined. The treated specimens were more resistant to wood decay fungi. Polyethylene and oxidized polyethylene wax were found to be particularly efficient. Although this treatment does not improve resistance to blue stain fungi, it reduces the sorption of water.ZusammenfassungSeit Jahrzehnten werden Wachse fast ausschließlich zur Oberflächenbehandlung von Holz verwendet, weil sie nur schwach in das Holz eindringen. Um das Eindringverhalten zu verbessern, wurden in dieser Studie fünf verschiedene Wasseremulsionen in unterschiedlichen Konzentrationen verwendet, und zwar zwei Montanwachse, Polyethylen, Ethylen-Copolymer und oxidiertes Polyethylenwachs. Die Resistenz von wachsbehandeltem Buchenholz (Fagus sylvatica) und Fichtenholz (Picea abies) gegen Weißfäule-, Braunfäule- und Bläuepilze wurde untersucht. Daneben wurden die Sorptionseigenschaften von wachsbehandeltem Holz bestimmt. Die behandelten Prüfkörper waren gegen Holz zerstörende Pilze resistenter, wobei sich Polyethylen und oxidiertes Polyethylenwachs als besonders wirksam erwiesen. Zwar wird mit dieser Behandlung die Resistenz gegen Bläue nicht verbessert, jedoch wird die Wasseraufnahme reduziert.

Decay resistance of wood treated with amino-silicone compounds

Abstract An amino-silicone (AS; amino-polydimethylsiloxane) micro-emulsion was tested for its suitability to preserve wood against basidiomycetes in a mini-block experiment and in a test according to the European standard (1996) EN 113. Decay resistance was assessed against the white rot fungi Trametes versicolor, Ceriporiopsis subvermispora, and Hypoxylon fragiforme, as well as the brown rot fungi Coniophora puteana, Antrodia vaillantii, Gloeophyllum trabeum and Serpula lacrymans. Pine sapwood and beech wood were treated with AS emulsions at solute concentration levels of 2%, 5% and 15%. The mini-blocks treated with 15% concentrations of AS resisted decay by T. versicolor and C. puteana over a long time (12 weeks), while samples treated with low and moderate concentrations underwent considerable mass losses. Accordingly, microscopic studies revealed a high degree of colonisation by the white rot fungus and loss of cell wall integrity (brown rot) in samples treated with 2% AS. At high AS content (15%), no or only initial stages of decay could be observed. In the European standard (1996) test EN 113, the mass loss in all fungal cultures except for the white rot ascomycete H. fragiforme was below 5%, when the samples were treated with 15% AS. The effect of low and moderate AS concentration on the decay resistance was dependent on the fungal strain. The mode of action of AS treatment against basidiomycete decay is discussed.

Changes in EPR spectra of wood impregnated with copper-based preservatives during exposure to several wood-rotting fungi

Summary The tolerance of various fungi against copper was examined. For this purpose, we impregnated Norway spruce (Picea abies) specimens with two different aqueous solutions: copper(II) octanoate with ethanolamine or copper(II) sulfate (cCu = 1.0 × 10−2 mol/l). Impregnated and unimpregnated test specimens were then exposed to brown rot fungi Antrodia vaillantii and Gloeophyllum trabeum or to white-rot fungi Schizophyllum commune and Trametes versicolor. After 2, 4, 6 and 12 weeks of exposure Electron Paramagnetic Resonance, Atomic Absorption Spectroscopy and mass loss measurements were performed. The results indicate that A. vaillantii, G. trabeum and T. versicolor transform copper(II) sulfate in wood into non-soluble, and therefore non-toxic, copper oxalate. The intensity of this reaction depends on the amount of excreted oxalic acid and was the highest for A. vaillantii and the lowest for T. versicolor. In the presence of ethanolamine, formation of insoluble copper oxalate was not possible and therefore, decay could not proceed. The major portion of copper remained in the wood and only minor amounts were in some cases translocated into nutrient media.

Microscopic analysis of the wood bond line using liquefied wood as adhesive

The bonding of beech (Fagus sylvatica L.) with liquefied wood (LW) causes deterioration of the wood surface, resulting in a high percentage of wood failure at a relatively low bond shear strength. Light microscopy, scanning electron microscopy, FT-IR micro-spectroscopy and elemental carbon, nitrogen and sulphur (CNS) analysis techniques were used to investigate the formation of such bonds. It was assumed that the degradation of lignin, hemicelluloses and parts of the cellulose occurred in the cells of the wood surface where the LW had been applied. At the elevated temperatures occurring during the bonding process, the deteriorated cells were carbonised to some extent. The weak boundary layer of the bond was determined to be a layer of delignified cells located between the zone of partly carbonised cells on the one side and the cells of the undamaged wood of the adherend on the other side. The bonds which formed during the bonding of wood with LW were found to be very untypical compared to bonds formed by synthetic wood adhesives. No adhesive film was formed, the adhesive-adherend interface was not clear and the cells of the adherend subsurface were damaged.

Patination of cherry wood and spruce wood with ethanolamine and surface finishes

SummariesThe appearance of age or the so-called patina of cherry wood and spruce wood was obtained by treatment with ethanolamine vapours. Chemical changes in the treated wood were investigated by FT-IR spectroscopy, electron paramagnetic resonance and nitrogen content analysis. It was shown that the use of aggressive and toxic ammonia could be replaced by fuming with ethanolamine. Extensive colour stability experiments of patinated cherry wood that was coated with linseed oil varnish, linseed oil, beeswax or nitro-cellulose lacquer indicated that the described antiquing method represents a new possibility for producing various wood products with the appearance of age.RésuméLe bois de cerisier et d’épicéa a pris un air antique, c’est à dire de la patination, après être traité à la vapeur d’éthanolamine. Des changements physiques dans le bois traité ont été investigués par le moyen de la spectroscopie TF-IR, de la résonance paramagnétique électronique et de l’analyse de la teneur en azote II a été montré que l’emploi de l’ammoniac qui est agressif et toxique pouvait être remplacé par une exposition à la vapeur d’éthanolamine. Des expériences extensives dans le domaine de la stabilité de la couleur du bois de cerisier patiné revêtu d’huile de lin, de vernis à l’huile de lin, de cire d’abeille ou de laque nitro-cellulosique ont indiqué que la méthode décrite de rendre plus antique l’apparence du bois représente une nouvelle possibilité dans le domaine de la production d’objets en bois qui aient l’air antique.ZusammenfassungKirsch- und Fichtenholz wurde durch Behandlung mit Ethanolamingas künstlich gealtert und die chemischen Veränderungen durch FT-IR-Spektroskopie, elektromagnetische Resonanz und Messungen des Stickstoffgehaltes ermittelt. Es zeigte sich, daß man die Verwendung von aggressivem und giftigem Ammoniak durch die Bedampfung mit Ethanolaminen ersetzen kann. Wir führten extensive Tests zur Farbstabilität von künstlich gealtertem Kirschbaumholz durch, das mit Leinöl, Leinöllack. Bienenwachs oder Nitrozelluloselack behandelt worden war. Die Tests zeigten, daß die Behandlung mit Ethanolaminen eine praktikable Methode ist, verschiedene künstlich gealterte Holzprodukte herzustellen.

Influence of carboxylic acids on fixation of copper in wood impregnated with copper amine based preservatives

The importance of copper/amine based preservatives is increasing. Leaching of copper from wood preserved with these solutions is still higher than leaching from wood impregnated with copper chromium ones. In order to decrease leaching, different carboxylic acids (octanoic, 2-ethylhexanoic, decanoic) were added to copper/amine/boron aqueous solutions. An experiment of leaching of copper from Norway spruce was performed according to the modified standard procedure (EN 1250). Results confirmed that carboxylic acids significantly improve copper fixation. The best fixation was determined in specimens impregnated with the preservative solutions consisting of copper, ethanolamine, boric acid and octanoic acid. From such wood, only 1.6% of copper was leached.

Performance of Waterborne Cu(II) Octanoate/Ethanolamine Wood Preservatives

Summary Various aqueous wood preservative solutions containing Cu(II) in the form of copper(II) sulphate or copper(II) octanoate, ethanolamine and in one case octanoic acid were investigated by spectrophotometry, polarography and Electron Paramagnetic Resonance (EPR) spectroscopy. Results have shown the same coordination environment around Cu(II) in all solutions with ethanolamine. Computer simulation of the EPR spectra also revealed that the coordination in the first coordination sphere of copper is the same at low concentration of ethanolamine. At 20% ethanolamine concentration, a mixture of two complexes (one with two nitrogens and the other with three) could be detected. The active compound in the investigated ethanolamine containing solutions is the same when previously synthesised copper(II) octanoate was used, or when copper(II) sulphate and octanoic acid were utilized instead. Fungicidal and leaching experiments with the treated wood resulted in the same conclusion: it is not necessary to use pre-synthesised copper(II) octanoate for the preparation of waterborne copper/ethanolamine wood preservatives. Preservative preparation time and costs can be reduced by simply dissolving copper(II) sulphate and octanoic acid in aqueous ethanolamine solutions.

Thermal modification of wax-impregnated wood to enhance its physical, mechanical, and biological properties

Abstract Thermal modification is the most important commercial modification procedure. Thermally modified (TM) wood has improved durability, but its performance does not meet expectations predominately under moist conditions. To reduce water uptake of TM wood, Norway spruce specimens were treated with suspensions of a natural wax by dipping impregnation (DipI) or by vacuum-pressure impregnation (VPI). Wax-treated specimens were subsequently TM at 185, 200, 215, and 230°C. Control specimens were heated up to 100°C only. Contact angle (CA), short-term and long-term water uptake, bending strength, and performance against wood decay fungi of the resulting material were determined. The results show that a combination of wax treatment and thermal modification have a synergistic effect that considerably improves hydrophobicity, reduces liquid water uptake, slows down water vapor uptake, and improves the resistance against fungal decay of the treated material.

Upgrading of spruce wood with ethanolamine treatment

Wood is the most abundant non-toxic, recycable and biodegradable natural material, valued as a construction material because of its appearance and its high strength at low density. On the other hand its biodegradability is an important drawback. Improvement of decay resistance of wood with ethanolamine is described in this paper. Ethanolamine chemically reacts with wood (Norway spruce sapwood) and does not evaporate from it. During this reaction, significant amounts of oxygen are consumed. Upgraded specimens show increased fungal activity and increased combustibility. The treatment of the spruce wood samples with aqueous solutions of ethanolamine resulted in colour changes.

The combined effect of wetting ability and durability on outdoor performance of wood: development and verification of a new prediction approach

Comprehensive approaches to predict performance of wood products are requested by international standards, and the first attempts have been made in the frame of European research projects. However, there is still an imminent need for a methodology to implement the durability and moisture performance of wood in an engineering design method and performance classification system. The aim of this study was therefore to establish an approach to predict service life of wood above ground taking into account the combined effect of wetting ability and durability data. A comprehensive data set was obtained from laboratory durability tests and still ongoing field trials in Norway, Germany and Sweden. In addition, four different wetting ability tests were performed with the same material. Based on a dose–response concept, decay rates for specimens exposed above ground were predicted implementing various indicating factors. A model was developed and optimised taking into account the resistance of wood against soft, white and brown rot as well as relevant types of water uptake and release. Decay rates from above-ground field tests at different test sites in Norway were predicted with the model. In a second step, the model was validated using data from laboratory and field tests performed in Germany and Sweden. The model was found to be fairly reliable, and it has the advantage to get implemented into existing engineering design guidelines. The approach at hand might furthermore be used for implementing wetting ability data into performance classification as requested by European standardisation bodies.