A Method for Determination of Absorption Isotherms at High Relative Humidity Levels: Measurements on Lime-Silica Brick and Norway Spruce (Picea abies(L.) Karst.)

Abstract

Link to publicationCitation for published version (APA): Fredriksson, M., & Johansson, P. (2016). A method for determination of absorption isotherms at high relative humidity levels: measurements on lime-silica brick and Norway spruce (Picea abies (L.) Karst.). Drying Technology, 34(1), 132-141. https://doi. AbstractThe relationship between the relative humidity and the moisture content of a material for relative humidity levels close to 100% can be studied using the pressure plate technique. However, this method is designed for desorption experiments and modifications are necessary in order to perform absorption experiments. This paper presents a method to condition samples to a uniform moisture content by absorption with the pressure plate technique. The specimens were suspended in magnetic clamps until the ceramic plate had equilibrated with the applied pressure and modifications were made so that water could circulate through the pressure plate cell.

Experimental techniques for characterising water in wood covering the range from dry to fully water-saturated

“…The decreasing sorption hysteresis at high RH might, however, be an artefact due to desorption being initiated from a non-saturated state (often by conditioning to 95% RH). Thus, in recent results by Fredriksson and co-workers (Fredriksson and Johansson 2016;Fredriksson and Thygesen 2017), sorption hysteresis in untreated Norway spruce gradually increases up to at least 95% RH (see Fig. 2).…”

“…lignin-rich middle lamella fragments) are over-represented in smaller size fractions that are more easily lost upon handling the milled material. Instead of milling, several studies have used wood slices cut with a microtome or razor blade to produce a large sample surface area while preserving the microscopic wood structure (Fredriksson and Thygesen 2017;Fredriksson et al 2010;Glass et al 2017;Hill et al 2015;Hosseinpourpia et al 2016;Song et al 2014), while a few use small wood blocks (Fredriksson and Johansson 2016). All of these studies use the automated humidity control by which RH is automatically changed upon reaching a specified mass stability (dm/dt) criterion.…”

“…2 a Sorption isotherms for desorption from water-saturated state and absorption from dry state for untreated and acetylated (R mod = 0.18) Norway spruce in the range of 0-97% relative humidity (RH). Based on data from Fredriksson and Johansson (2016), Fredriksson et al (2013) at 20°C and from authors at 25°C (dm/dt = 0.0005%/min). Note that the desorption and absorption isotherms do not coalesce at 97% RH; b absolute sorption hysteresis of untreated wood from moisture content data acquired with automated sorption balances.…”

“…Note that the desorption and absorption isotherms do not coalesce at 97% RH; b absolute sorption hysteresis of untreated wood from moisture content data acquired with automated sorption balances. Based on data for Norway spruce (Fredriksson and Johansson 2016;Fredriksson and Thygesen 2017;Källbom 2015;Sedighi-Gilani and Schwarze 2015) and Sitka spruce ). Note that in all studies except (Fredriksson and Johansson 2016;Fredriksson and Thygesen 2017) Besides deriving MC in equilibrium with various climates, automated sorption balances have been used for studying the kinetics of sorption.…”

“…Based on data for Norway spruce (Fredriksson and Johansson 2016;Fredriksson and Thygesen 2017;Källbom 2015;Sedighi-Gilani and Schwarze 2015) and Sitka spruce ). Note that in all studies except (Fredriksson and Johansson 2016;Fredriksson and Thygesen 2017) Besides deriving MC in equilibrium with various climates, automated sorption balances have been used for studying the kinetics of sorption. In many polymeric materials, the sorption process exhibits two-stage behaviour (Christensen and Kelsey 1959;Crank 1953;Kelly and Hart 1970;Newns 1956) and cannot be explained by Fickian diffusion into the material.…”