Combined bound water and water vapour diffusion of Norway spruce and European beech in and between the principal anatomical directions

Sonderegger, Walter; Vecellio, Manuele; Zwicker, Pascal; Niemz, Peter

doi:10.1515/hf.2011.091

Cited by 22 publications

(13 citation statements)

References 17 publications

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“…A few experiments have been performed to investigate the water states and diffusion constants in unmodified wood [144]. As the amount of water increases, diffusion of water increases as assessed experimentally using water absorption studies [145][146][147], NMR spin-spin relaxation studies [148], and QENS [149]. The QENS results suggest the presence of at least two distinct water populations in wood, and is able to quantify their dynamic state using a jump diffusion model [149].…”

Section: Water Diffusion and Plasticization In Wood Polymersmentioning

confidence: 99%

Effects of Moisture on Diffusion in Unmodified Wood Cell Walls: A Phenomenological Polymer Science Approach

Jakes

Hunt

Zelinka

et al. 2019

Forests

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Despite the importance of cell wall diffusion to nearly all aspects of wood utilization, diffusion mechanisms and the detailed effects of moisture remain poorly understood. In this perspective, we introduce and employ approaches established in polymer science to develop a phenomenological framework for understanding the effects of moisture on diffusion in unmodified wood cell walls. The premise for applying this polymer-science-based approach to wood is that wood polymers (cellulose, hemicelluloses, and lignin) behave like typical solid polymers. Therefore, the movement of chemicals through wood cell walls is a diffusion process through a solid polymer, which is in contrast to previous assertions that transport of some chemicals occurs via aqueous pathways in the cell wall layers. Diffusion in polymers depends on the interrelations between free volume in the polymer matrix, molecular motions of the polymer, diffusant dimensions, and solubility of the diffusant in the polymer matrix. Because diffusion strongly depends on whether a polymer is in a rigid glassy state or soft rubbery state, it is important to understand glass transitions in the amorphous wood polymers. Through a review and analysis of available literature, we conclude that in wood both lignin and the amorphous polysaccharides very likely have glass transitions. After developing and presenting this polymer-science-based perspective of diffusion through unmodified wood cell walls, suggested directions for future research are discussed. A key consideration is that a large difference between diffusion through wood polymers and typical polymers is the high swelling pressures that can develop in unmodified wood cell walls. This pressure likely arises from the hierarchical structure of wood and should be taken into consideration in the development of predictive models for diffusion in unmodified wood cell walls.

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Section: Water Diffusion and Plasticization In Wood Polymersmentioning

confidence: 99%

Effects of Moisture on Diffusion in Unmodified Wood Cell Walls: A Phenomenological Polymer Science Approach

Jakes

Hunt

Zelinka

et al. 2019

Forests

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“…These differences can be partially explained by the different densities of the radial and tangential specimens and partially due to the different thermal conductivity of wood in the radial and tangential directions (λ R > λ T ). These differences can be attributed to the significant number of wood rays in hardwoods and their orientation [28,29]. In addition, in the tangential section reasonably the ratio of earlywood and latewood is different, depending by the position if close to the pith or far from the pith [3].…”

Section: Resultsmentioning

confidence: 99%

“…Heat treatment of beech blocks were performed by Hakkou et al (2005) in France, in a reactor placed in an oven, the wood surface started to be hydrophobic (CA > 90°) after 120 °C [21]. CA characterized on heat-treated beech wood at 240 °C in an industrial oven showed that the variation after and before processing (∆θa = 16.2°) was low compared with other species (spruce = 44.7°, pine = 62.4° poplar = 85.8°) [28]. The value of ∆θa for beech processed by contact heating for radial specimens (∆θa = 200/20R-REFR) was 24.0° and 5.6° for tangential (∆θa = 200/20T-REFT).…”

Section: Resultsmentioning

confidence: 99%

Effect of One-Sided Surface Charring of Beech Wood on Density Profile and Surface Wettability

et al. 2021

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One-sided surface charred European beech wood (Fagus sylvatica L.) was studied. Radial and tangential specimens of dimensions of 50 × 25 × 350 mm were one-sided surface charred at 200, 250, 300, 350, and 400 °C for various times using a contact heating system. Specimens of dimensions of 50 × 25 × 50 mm3 were prepared for treatment intensity analysis and its effect on surface wettability. Density profiles of the radial and tangential charred specimens were determined using X-ray densitography with a resolution of 0.05 mm. The wettability of the one-sided surface charred wood specimens was analyzed via contact angle, measured using the sessile drop method and determined over 10 to 150 s. The oven-dried specimens were partially submerged in water and water uptake was recorded after 2, 4, 6, 8, 10, 48, and 72 h according to EN-927-5. The surface density of the radial specimen groups charred at 200 °C for 6 min and 250 °C for 4 min decreased by about 4.5 to 8.2%. With increasingly severe charring, the surface density decreased by about 15.5 to 33.5%. A mild charring process produced a surface charred layer of approx. 2 mm, while higher temperatures and longer times affected the density up to 4–6 mm beneath the surface. Differences were found between the water uptake of the radial and tangential charred beech specimens. The most significant decrease of 56% in water uptake was recorded for the radial group prepared at 200 °C for 20 min after floating in water for 72 h. Water uptake in the radial groups modified at 250 °C for 4 and 6 min after 72 h decreased by 38% and 36%, respectively. The tangential groups did not show any statistically significant decrease. The average water uptake of the groups charred at 200 °C for 20 min, 350 °C for 2 min and 400 °C for 1 min was greater than that of the reference; the variability of the measured data was significantly greater due to the highly anisotropic character of the tangential specimens. Micro cracks were also visible on the surface. Concluding from the results of this study, one-sided surface charred beech wood exhibits increased potential in terms of wood–water related properties when a temperature range of 200–400 °C is applied.

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“…The diffusion coeffi cient and Biot number, evaluated from adsorption experiment of beech wood in humid air are random variables (Comstock, 1963;Dekrét and Kurjatko, 1986;Hrčka, 2008;Sonderegger et al, 2011). The critical p-level value was set to 5 % as a variability of data can be assumed.…”

Section: Rezultati I Raspravamentioning

confidence: 99%

Finite Changes of Bound Water Moisture Content in a Given Volume of Beech Wood

Hrčka

2015

Drvna ind.

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Combined bound water and water vapour diffusion of Norway spruce and European beech in and between the principal anatomical directions

Cited by 22 publications

References 17 publications

Effects of Moisture on Diffusion in Unmodified Wood Cell Walls: A Phenomenological Polymer Science Approach

Effects of Moisture on Diffusion in Unmodified Wood Cell Walls: A Phenomenological Polymer Science Approach

Effect of One-Sided Surface Charring of Beech Wood on Density Profile and Surface Wettability

Finite Changes of Bound Water Moisture Content in a Given Volume of Beech Wood

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