Abstract
The aim of this paper was to analyze selected properties of beech wood (Fagus sylvatica L.) treated by one-sided surface charring. Specimens were one-side charred with a hot plate using several time-temperature combinations (from 200 to 400 °C). Characteristics such as colour, discoloration, surface roughness, fire resistance, total carbohydrate content at several wood layers and decay resistance were evaluated. Surface charring was applied to the radial and tangential surfaces. Colour measurements showed that the surface of the wood turned grey due to charring. In addition to colour measurements, other experiments showed significant differences between radial and tangential specimens due to their different structures. The higher the temperature used in treating them, the lower the roughness values for radial specimens, while the trend for tangential specimens was the opposite. A smoother surface is more fire resistant, so radial specimens are generally better in this regard. Tangential specimens are more susceptible during preparation to forming cracks that impair flame resistance because a continuous protective densified layer is not formed. The determination of total carbohydrates revealed significant changes at various wood depths after surface charring. These changes were more predictable in radial specimens due to the annual ring orientation, because each layer consisted of a similar earlywood/latewood ratio. Finally, when decay resistance was assessed, weight loss was found to be lower in all specimens than in the references. The results suggest that charring at a particular combination of temperature and time improved the investigated properties of the surface-modified beech.
Highlights
The method of preserving the surfaces of wood by charring was probably unknowingly used in history when people learned to control fire
We studied European beech (Fagus sylvatica L.) wood obtained from a forest enterprise in Moravia, a region of the Czech Republic
The colour space CIEL*a*b* of beech wood charred with different temperatures and times was investigated
Summary
The method of preserving the surfaces of wood by charring was probably unknowingly used in history when people learned to control fire. One of the first scientific experiments on the verification of the wood charring effectiveness was carried out by Graham and Miller in 1957 on fence posts [6]. According to their results, the technique was in preserving wood from decay not as effective as the application of banned or restricted products, such as creosote and other hazardous compounds. A practical experiment in 2019, based on traditional Japanese practice, proved that a protective effect could be achieved, but it has been suggested that this cannot be done ecologically, due to the large gas consumption required for the surface charring [7]
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