Nejc Thaler

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.

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.

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.

Intra-annual dynamics of phloem formation and ultrastructural changes in sieve tubes in Fagus sylvatica

Despite increased interest in the timing and dynamics of phloem formation, seasonal changes in the structure of phloem sieve elements remain largely unexplored. To understand better the dynamics of phloem formation and the functioning of sieve tubes in the youngest phloem in Fagus sylvatica L., we investigated repeatedly taken phloem samples during the growing season of 2017 by means of light microscopy, and transmission and scanning electron microscopy. Phloem formation started with the expansion of the overwintered early phloem sieve tubes adjacent to the cambium and concurrent cambial cell production. The highest phloem growth rate was observed in general 1 week after the onset of cambial cell production, whereas the transition from early to late phloem occurred at the end of May. Cambial cell production ceased at the end of July. The final width of the phloem increment was 184 ± 10 μm, with an early phloem proportion of 59%. Collapse of older phloem tissue is a progressive process, which continuously occurred during the sampling period. Collapse of early phloem sieve tubes started shortly after the cessation of cambial cell production. Prior to the onset of radial growth, late phloem from the previous year represented 80% of the total non-collapsed part; during the growth period, this percentage decreased to 20%. Differences were observed in both sieve tube ultrastructure and sieve plate geometry between the youngest and older phloem. However, sieve plates were never completely occluded by callose, suggesting that processes affecting the functionality of sieve tubes may differ in the case of regular collapse or injury. The youngest parts of the phloem increment from the previous year (i.e., previous late phloem) continue functioning for some time in the current growing season, but the two-step development of overwintered phloem cells also ensures a sufficient translocation pathway for photosynthates to the actively growing tissues.

Mechanical and Fungicidal Properties of approximately 100 Years Old Oak, Beech and Spruce Wood Beams

The aim of this preliminary study was to investigate differences in mechanical and fungicidal properties of three different wood species (English oak (Quercus sp.), common beach (Fagus sylvatica) and Norway spruce (Picea abies)) specimens that were in indoor use for several decades, compared to control specimens of freshly cut timber. The collected material was cut to smaller specimen and conditioned in standard climate prior to further analysis. Mechanical, fungicidal, and sorption properties were determined according to the standard procedures. Our results show that mechanical properties of oak wood do not deteriorate in the investigated time frame. On the other hand, resistance of the wood against fungi decreases over time. The reason for this is yet to be confirmed, it could be due to the degradation of secondary metabolites. Similar results were observed for spruce wood as well. There were no statistically significant differences in mechanical properties of old and new spruce wood. In contrary to oak wood, there were also no significant differences in fungicidal properties, considering that spruce wood has lower durability than oak wood. Same as with oak wood, G. trabeum was found to be the most aggressive fungus. Ageing of beech wood resulted in a big drop in all of the tested mechanical properties, but showed no significant differences in fungicidal properties. Here is where the low durability of beech wood really shows. The old beech wood specimens were moderately deteriorated by insects and fungi, which was the reason for loss of bending and compressive strength.