Moisture Sorption of Wood Surfaces Modified by One-Sided Carbonization as an Alternative to Traditional Façade Coatings

Kymäläinen, Maija; Dömény, Jakub; Rautkari, Lauri

doi:10.3390/coatings12091273

Cited by 13 publications

(16 citation statements)

References 46 publications

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“…The samples were exposed to a temperature of 320 °C for a duration of 30 min. This regime was chosen based on previous tests [ 6 , 7 ] to avoid surface cracking and create a thick transition layer. The flame charring was implemented outdoors, moving the torch slowly along the length of a one-meter board.…”

Section: Methodsmentioning

confidence: 99%

“…The basic process of surface carbonization is quite simple and relies on high temperatures that degrade the surface to a carbonaceous residue, or charcoal. The techniques include the traditional “free” flame charring, where the boards are set on fire by ignition flame [ 3 , 4 ], and the more controlled gas flame charring, where boards are either charred by a handheld torch or conveyed beneath static torches [ 5 , 6 , 7 ]. Not yet commercialized, the contact charring technique relies on the use of a heated plate in tight contact with the modified wood surface, providing a highly repeatable and controlled result [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ].…”

Section: Introductionmentioning

confidence: 99%

“…It has previously been shown that a flame charred surface is rather inert against weathering damage, thus whether it would also provide protection against decay was further examined. Contact charring of wood differs from flame charring in terms of exposure temperature and duration, and the resulting product presents a smooth, hard surface with highly improved sorption properties [ 7 ]. For this reason, contact and flame charred wood surfaces were compared.…”

Section: Introductionmentioning

confidence: 99%

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Decay Resistance of Surface Carbonized Wood

et al. 2022

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Surface carbonization, or charring, of wood is a one-sided modification method primarily intended for protection of exterior cladding boards. The heavily degraded surface acts as a barrier layer shielding the interior from environmental stresses, and as such acts as an organic coating. To test the durability of surfaces created in this manner, unmodified, contact charred, and flame charred spruce and birch samples were exposed to the brown rot fungus Coniophora puteana and white rot fungus Trametes versicolor for a period of nine weeks. All sides of the samples except the modified surfaces were sealed to investigate the protective effect of the surface. Mass losses were greatest for unmodified references (up to 60% and 56% for birch and spruce, respectively) and smallest for contact charred samples (up to 23% and 32%). The wood below the modified surfaces showed chemical changes typical of brown rot and simultaneous white rot. The measured glucosamine content revealed fungal biomass in both the modified surface as well as the layers beneath. According to the recorded values, the fungal biomass increased below the surface and was higher for flame charred samples in comparison to contact charred ones. This is likely due to the more intact, plasticized surface and the thicker thermally modified transition zone that restricts fungal growth more effectively in contact charred samples in comparison to the porous, cracked flame charred samples. Scanning electron microscope images verified the results by revealing fungal hyphae in all inspected wood types and species.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Decay Resistance of Surface Carbonized Wood

et al. 2022

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“…The SF group showed the highest surface roughness with R a of 143 µm. The increased surface roughness is caused by the charring process: a heterogeneous modi ed layer with variable sized cracks is formed due to the uneven action of the ame on the surface during the process (Ebner 2021), while a more homogeneous surface can be achieved by using the hot plate (Šeda et al 2021;Kymäläinen et al 2022c). However, it is necessary to use appropriate parameters of the modi cation process.…”

Section: Surface Roughnessmentioning

confidence: 99%

“…The process utilizes a heated surface that can consistently maintain a targeted temperature for the desired treatment duration. The resulting surface is hard, smooth and hydrophobic due to ow and plasticization of structural components and migration and condensation of extractives (Kymäläinen et al 2018; Kymäläinen et al 2022c). This method is still under development, but the experimental pilot scale results presented by Kymäläinen et al (2020) were promising for potential commercial development.…”

Section: Introductionmentioning

confidence: 99%

Evaluating the quality of surface carbonized woods modified with a contact charring or a gas flame charring technique

Kymäläinen

Dömény

Schwarzkopf³

et al. 2022

Preprint

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Surface carbonization, or charring, of wooden exterior cladding boards is a modification method that creates a fully organic barrier layer in resemblance to a coating. The process effectively degrades the wood and transforms it into a carbonaceous residue that protects the underlying unmodified wood from environmental stresses. The surface quality of wood modified in this manner is a combination of several factors and depends on the manufacturing method and wood species. To assess the quality of spruce and birch modified with contact and flame charring techniques, several experiments were set up from the nanoscale to macroscopic evaluation of surface resistance to different stresses. The degree of changes in elemental composition scale with the modification severity with little differences between wood species. The carbon structures analyzed by high resolution transmission electron microscopy (HR-TEM) were found to be amorphous, but the electron energy loss spectroscopy (EELS) revealed higher ordering with what is assumed to be random graphitic stacking of carbon sheets. These carbon-carbon bonds are stable, so a higher ordering is hypothesized to induce improved resistance to exterior stresses. The scanning electron microscopy (SEM) revealed a clear difference between contact charred and flame charred woods. The selected contact charring temperature was not high enough to induce the transformation of cell walls from anisotropic into an isotropic material but provided other benefits such as a relatively crack-free, smooth and scratch resistant surface. Surface roughness was able to adequately predict the surface quality of the contact charred samples and scratch tests were found to be suitable for evaluating the mechanical stress resistance of the surface instead of abrasion. In terms of overall quality, birch instead of spruce was concluded to better respond to both charring methods, although contact charring eliminates some species-specific characteristics, resulting in more homogeneous surfaces.

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