The Impact of Paraffin-Thermal Modification of Beech Wood on Its Biological, Physical and Mechanical Properties

Abstract

The European beech (Fagus sylvatica L.) wood was thermally modified in the presence of paraffin at the temperatures of 190 or 210 °C for 1, 2, 3 or 4 h. A significant increase in its resistance to the brown-rot fungus Poria placenta (by 71.4%–98.4%) and the white-rot fungus Trametes versicolor (by 50.1%–99.5%) was observed as a result of all modification modes. However, an increase in the resistance of beech wood surfaces to the mold Aspergillus niger was achieved only under more severe modification regimes taking 4 h at 190 or 210 °C. Water resistance of paraffin-thermally modified beech wood improved—soaking reduced by 30.2%–35.8% and volume swelling by 26.8%–62.9% after 336 h of exposure in water. On the contrary, its mechanical properties worsened—impact bending strength decreased by 17.8%–48.3% and Brinell hardness by 2.4%–63.9%.

Beech wood thermally modified in the melt of polyethylene glycol

“…In this experiment, in contrast to the experiment with the paraffin-thermally modified beech wood (Reinprecht and Repák 2019), the white-rot fungus T. versicolor did not cause higher weight losses of the PEG-thermally modified beech wood than the brownrot fungus P. placenta. However, comparing with the paraffin-thermally modified beech wood, when its resistance to rot increased always on the 99.9% significance level (Reinprecht and Repák 2019), the anti-rot effect of the PEG-thermal modification modes was clearly lower (Table 1). This could also be caused by a washout of water soluble PEG macromolecules from modified wood during the mycological testso an initial water washout of specimens by EN 84 (1997) would be appropriate.…”

“…Comparing analogous methods of wood thermall modification in melts, i.e., the paraffin-thermal method (Reinprecht and Repák 2019) and the PEG-thermal method present in this work, it can be concluded that PEG 6000 has a lower inhibitory effect against rot by decaying fungi compared to paraffin. This can be attributed mainly to the hydrophilic nature of PEG.…”

“…Fungal attack of specimens was performed in Petri dishes with a diameter of 100 mm during 6 weeks by a modified standard EN 113 (1996), i.e., in accordance with fungal attacks of the paraffin-thermally treated beech wood specimens (Reinprecht and Repák 2019) and with the rapid mycological screening test by Van Acker et al (2003).…”

“…Biological resistance of the thermally modified wood increases due to application higher temperatures, usually from 160 to 220 °C or in the absence of oxygen also up to 260 °C (Rapp and Sailer 2001;Reinprecht et al 2007;Yilgör and Kartal 2010;Westin et al 2013). In comparison to the most common thermal modification process in hot air, a higher resistance of wood to moulds, decaying fungi, and water is ensured when its heating is performed in hot plant oils, melt waxes, or some other liquid substances (Rapp and Sailer 2001; Wang and Cooper 2005;Reinprecht et al 2007;Hasan et al 2008;Reinprecht and Vidholdová 2008;Dubey et al 2012;Reinprecht and Repák 2019). For example, non-toxic and environmentally acceptable hydrophobic paraffin and various waxes decrease the water absorption rate of wood (Reinprecht and Repák 2019), improve its dimensional stability (Scholz et al 2009), and also improve its resistance to termites (Scholz et al 2010;Esteves et al 2014).…”

“…In comparison to the most common thermal modification process in hot air, a higher resistance of wood to moulds, decaying fungi, and water is ensured when its heating is performed in hot plant oils, melt waxes, or some other liquid substances (Rapp and Sailer 2001; Wang and Cooper 2005;Reinprecht et al 2007;Hasan et al 2008;Reinprecht and Vidholdová 2008;Dubey et al 2012;Reinprecht and Repák 2019). For example, non-toxic and environmentally acceptable hydrophobic paraffin and various waxes decrease the water absorption rate of wood (Reinprecht and Repák 2019), improve its dimensional stability (Scholz et al 2009), and also improve its resistance to termites (Scholz et al 2010;Esteves et al 2014). On contrary, deteriorated are mechanical properties of thermally modified woods, mainly their strength and less significantly their modulus of elasticity (Hill 2006;Sandberg et al 2021).…”