Boštjan Lesar

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.

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.

Sorption Properties of Wood Impregnated with Boron Compounds, Sodium Chloride and Glucose

Chemical protection is one of the possible treatment processes that influence the sorption characteristics of wood. In the present research we have investigated the influence of biocides (boric acid, borax) and their concentrations on the sorption characteristic of impregnated wood. For comparison, two other chemicals were included in the research as well (NaCl and glucose). The equilibrium moisture content during the adsorption and desorption process at five levels of relative humidity (ϕ1 = 20%, ϕ2 = 33%, ϕ3 = 65%, ϕ4 = 88%, and ϕ5 = 98%) was monitored. The results showed that impregnation does not influence the wood moisture content of specimens conditioned at low relative air humidity. In the upper hygroscopic region, moisture content is significantly influenced by the concentration and properties of impregnation chemicals. The Guggenheim-Andersen-deBoer (GAB) and Dent models of sorption isotherms was fitted to experimental data to explain the sorption mechanisms in detail.

Re-evaluation of fungicidal properties of boric acid

AbstractMinimal inhibitory fungicidal concentrations of one of the most important biocides were determined in nutrient medium and on impregnated wood specimens. The results showed, that brown rot fungi are more sensitive to boric acid than white rot ones. To inhibit growth of wood decay fungi, lower minimal effective retentions have been determined than reported in previous publications.

Utilization of recycled wood in biorefineries: preliminary results of steam explosion and ethanol/water organosolv pulping without a catalyst

With overall higher use of wood and wooden materials in the future, the importance of recycled wood will increase. Recycled wood is currently used for the production of wood based composites and for combustion. In the future, use of recycled wood will also be important as feedstock for biorefineries for the production of bio-based chemicals and biofuels. The present paper gives preliminary results on the feasibility of A I recycled wood (German classification, natural wood only treated mechanically) in a steam explosion and organosolv pre-treatment process. The presence of inorganic pollutants and non-wooden material in recycled wood material was investigated. The effect of recycled wood heterogeneity (e.g., variable wood species and wide particle size distribution) on performance of wood pretreatment and subsequent enzymatic hydrolysis was also evaluated. Microeconomic analysis of lignocellulosic feedstock for a biorefinery using organosolv cooking was calculated with various price scenarios and various proportions of recycled wood instead of fresh beech chips. The results show that the concentration of inorganic pollutants is higher than in fresh wood but below the limit values for polluted wood. Preliminary results on steam explosion and ethanol based organosolv cooking without an acid catalyst showed typical behaviour of softwood for recycled wood of A I quality in respect of hydrolysability, thus being a potential future raw material for sugar production. A I recycled wood can be used in a biorefinery without major problems and can significantly improve the economics of investment in an industrial scale biorefinery.

Rezultati izlaganja nezaštićenog drva i drva zaštićenog bakar- etanolaminom utjecaju morske vode u luci Koper, Slovenija

The application of wood in seawater is one of the most challenging. Impregnated wood is exposed to leaching and to various marine borers, Limnoria sp. and Teredo sp. being the most important ones. The present research investigated the durability of pine wood impregnated with copper-amine based preservative solution (Silvanolin) of different concentrations exposed to the seawater according to EN 275 standard. Performance of Silvanolin treated wood was compared to the performance of reference wood (Quercus sp., Castanea sativa, Larix decidua). After 10, 18 and 32 months of exposure, specimens were removed and assessed. The results show clearly that the reference wood species were completely degraded after 10 months of exposure. On the other hand, it became evident that Silvanolin prolonged the service life of wood exposed to the sea. The specimens impregnated with the lowest concentration of preservative solution (cCu = 0.31 %) were slightly decayed. The specimens, impregnated with higher concentrations of copper (cCu > 0.31 %), showed almost no defects after expsore to marine borers.

Performance of wood impregnated with N-methylol and copper based aqueous solutions

AbstractThe combination of copper and N-methylol compounds considerably improves the performance against copper sensitive fungi (G. trabeum and T. versicolor), while the fungicidal effect against copper tolerant strain (A. vaillantii) remained insufficient. Addition of N-methylol compounds to copper solution significantly reduces leaching from wood blocks impregnated with the solution of the lowest copper concentration (cCu =0.1%), and less notably reduces leaching from wood blocks impregnated with solutions of higher copper contents (cCu=0.5%).

Short-term performance of wooden windows and facade elements made of thermally modified and non-modified Norway spruce in different natural environments

ABSTRACT Thermally modified wood is becoming an increasingly popular material for different applications in buildings. Laboratory tests indicated a positive effect of thermal modification on durability, dimensional stability and thermal conductivity of wood. Therefore, windows and facade elements made of thermally modified Norway spruce and non-modified Norway spruce were tested in the field and installed in different test objects which were exposed at five locations in Europe (Slovenia, Germany, Sweden, and Spain). Results from monitoring showed that elements and windows made of thermally modified spruce (TMS) had considerably lower wood moisture content compared to the ones made of non-modified spruce and that wax further positively influenced moisture performance. Colour changes of TMS were more intensive compared to non-modified spruce but were successfully retarded by adding pigments to the wax. Mould and stain growth was largely dependent on the location, amount of precipitation and relative humidity.

Leaching of boron from wood impregnated with preservative solutions based on boric acid and liquefied wood

Reducing boron leaching from impregnated wood has been one of the most challenging tasks for at least 50 years. In order to slow down the leaching of boron, aqueous solutions of boric acid were combined with liquefied spruce wood. The results clearly showed that leaching of boron from spruce wood impregnated with preservative solutions based on boric acid and liquefied wood was significantly reduced.

Performance of wood in the Franja partisan hospital

ABSTRACT Wood is one of the most important construction materials and its use in building applications has further expanded in recent decades. In order to enable even more extensive and reliable use of wood, factors affecting wood’s service life need to be understood. It is well known that fungal degradation of wood is predominantly affected by moisture content (MC) and temperature (T). In order to elucidate the influence of these two factors, long-term monitoring of T, relative humidity (RH) and wood MC was carried out at the WWII partisan hospital Franja, Slovenia. The results clearly showed that fungal degradation of wood is influenced by MC and T. A model to predict brown and white/soft rot decay of wood was applied to predict the expected service lives of different building components of the hospital cabins. The predicted times until onset of decay were well in accordance with findings made during visual assessments and drill resistance measurements at this historical site. The monitoring concept in combination with a mathematical decay prediction model can provide accurate data and valuable guidance for building modern structures and maintaining the cultural heritage.