Surface Modification of Spruce and Fir Sawn-Timber by Charring in the Traditional Japanese Method-Yakisugi.

David Hans Ebner,Petr Čermák,Marius-Catalin Barbu,Josef Klaushofer

doi:10.3390/polym13101662

David Hans Ebner, Petr Čermák + Show 2 more

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https://doi.org/10.3390/polym13101662

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Abstract

The traditional Japanese method of wood surface charring was studied. To perform the surface charring, three sawn Norway spruce and Silver fir wood boards of dimension 190 × 24 × 4000 mm3 were tied together to act as a chimney and charred in a short time (3–4 min) with open flame at a temperature above 500 °C. Temperature inside the chimney was recorded on the three different positions during the charring process. Surface temperature of spruce increased from 0 °C to 500 °C in approx. 120–300 s while fir increased in approx. 100–250 s. The thickness of the charred layer and the resulting cupping effect were investigated at the different heights of the chimney to evaluate its variability. Temperature achieved during the charring process was sufficient to get a significant charred layer of 2.5 and 4.5 mm on average for spruce and fir samples, respectively. The analyzed samples showed a significant cupping effect to the charred side with no difference between the annual ring orientation of sawn boards. Spruce exhibit a more significant cupping effect when compared to fir, i.e., 3.2–6 mm and 2.2–4.5 mm, respectively. Furthermore, the pH values of charred samples increased significantly, which could be an indication of improved resistance against wood-decay fungi. For better insight into the traditional charring method, further studies should be carried out to execute the charring process in a consistent quality and therefore fully exploit its potential.

Highlights

Nowadays, the forest and wood-working products industry has to meet new challenges in terms of sustainable wood protection, especially when it comes to house facades made of sawn-timber claddings
To perform the surface charring, three sawn Norway spruce and Silver fir wood boards of dimension 190 × 24 × 4000 mm3 were tied together to act as a chimney and charred in a short time (3–4 min) with open flame at a temperature above 500 ◦C
Spruce exhibit a more significant cupping effect when compared to fir, i.e., 3.2–6 mm and 2.2–4.5 mm, respectively

Summary

Introduction

The forest and wood-working products industry has to meet new challenges in terms of sustainable wood protection, especially when it comes to house facades made of sawn-timber claddings. There are currently many scientific studies on the subject of preserving timber against various environmental impacts [1,2] Wood modifications, such as thermal, chemical, or mechanical treatments, to improve the physico-mechanical properties are available [2,3]. A contact heating system by hot plate used for one-sided surface charring of wood allows greater control of the process conditions and provide uniform charred surface at temperature range of 200–400 ◦C [4,5,6,7]. Recent studies proved that the protective properties of charring were influenced by the wood species (spruce and pine), the temperature and time of charring, and the evenness of treatment. The charred surface modified using hot plate method is uniform, less brittle, and non-coloring when touched, when compared to the traditional Japanese process

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