Effects of Cyclic Changes in Relative Humidity on the Sorption Hysteresis of Thermally Modified Spruce Wood

Majka, Jerzy; Czajkowski, Łukasz; Olek, Wiesław

doi:10.15376/biores.11.2.5265-5275

Cited by 28 publications

(14 citation statements)

References 20 publications

(26 reference statements)

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“…In both cases, a noticeable different adsorption curve, ie lower EMC values, were seen for the first cycle compared with the following two cycles. This indicates that a part of the EMC reduction effect resulting from the thermal treatment is reversible because of moisture sorption, in line with Hill et al (2012) and Majka et al (2016). Stronger drying 2.…”

Section: Sorption Propertiesmentioning

confidence: 78%

“…Earlier studies of the water vapor sorption behavior of TMW have shown significant reduction in hygroscopicity compared with UW controls, eg for Scots pine (Engelund et al 2010;Hill et al 2012), Sitka spruce (Hill et al 2010;Endo et al 2016) and Norway spruce (Pfriem et al 2010;Källbom et al 2016;Majka et al 2016). The preferential thermal degradation of hemicelluloses, which contain the highest concentration of water-accessible hydroxyl groups among the cell wall polymers (Runkel 1954;Runkel and Lüthgens 1956), reduces the number of water sorption sites in wood.…”

Section: Introductionmentioning

confidence: 98%

“…Furthermore, cross-linking reactions within the cell wall matrix limit the access to the remaining sorption sites (Tjeerdsma et al 1998). However, recent studies (Hill et al 2012;Majka et al 2016) evidenced the occurrence of a reversible reduction in hygroscopicity in addition to any irreversible changes. This conclusion was based on the analysis of several adsorption-desorption cycles for TMW using a so-called dynamic vapor sorption (DVS) technique or different relative humidity (RH) conditions controlled by salt solution, showing a decrease of sorption hysteresis comparing the first with the second sorption cycle.…”

Section: Introductionmentioning

confidence: 99%

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Sorption and Surface Energy Properties of Thermally Modified Spruce Wood Components

Källbom

Altgen

Militz

et al. 2018

W&FS

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The objective of this work is to study the water vapor sorption and surface energy properties of thermally modified wood (TMW) components, ie wood processing residuals in the form of sawdust. The thermal modification was performed on spruce wood components using a steam-pressurized laboratoryscale reactor at two different temperature (T ) and relative humidity (RH) conditions, T ¼ 150°C and RH ¼ 100% (TMW150), and T ¼ 180°C and RH ¼ 46% (TMW180). A dynamic vapor sorption (DVS) technique was used to determine water vapor sorption isotherms of the samples for three adsorption-desorption cycles at varying RH between 0% and 95%. Inverse gas chromatography (IGC) was used to study the surface energy properties of the samples, including dispersive and polar characteristics. The DVS results showed that the EMC was reduced by 30-50% for the TMW samples compared with control samples of unmodified wood (UW) components. A lower reduction was, however, observed for the second and third adsorption cycles compared with that of the first cycle. Ratios between EMC of TMW and that of UW samples were lower for the TMW180 compared with the TMW150 samples, and an overall decrease in such EMC ratios was observed at higher RH for both TMW samples. The IGC results showed that the dispersive contribution * Corresponding author † SWST member to the surface energy was higher at lower surface coverages, ie representing the higher energy sites, for the TMW compared with the UW samples. In addition, an analysis of the acid-base properties indicated a higher K B than K A number, ie a higher basic than acidic contribution to the surface energy, for all the samples. A higher K B number was also observed for the TMW compared with the UW samples, suggested to relate to the presence of ether bonds from increased lignin and/or extractives content at the surface. The K B was lower for TMW180 compared with TMW150, as a result of higher modification temperature of the first, leading to cleavage of these ether bonds.

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Section: Sorption Propertiesmentioning

confidence: 78%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Sorption and Surface Energy Properties of Thermally Modified Spruce Wood Components

Källbom

Altgen

Militz

et al. 2018

W&FS

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“…180 and 220 °C, were set during the main phase of the modification. The duration of the main phase was 1 h. Majka et al (2016) showed that duration of the main phase of the laboratory-based thermal modification has no significant influence on mass loss and hygroscopic properties. The target temperature values were kept constant during the main phase.…”

Section: Thermal Modificationmentioning

confidence: 94%

Effects of heat treatment on thermal properties of European beech wood

2020

Self Cite

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Beech wood, due to its properties, is one of the most versatile and successfully used construction materials. The wood properties could even be improved, and among different wood modification processes, the thermal modification approach is usually considered as an environment-friendly technology based only on the heat and water application during wood treatment. Changes in material properties resulting from the thermal treatment of wood increase applicability of this material, but on the other hand, detailed knowledge of the modified properties is definitely necessary for the proper application of such materials to construction engineering. Unfortunately, credible data on thermal characteristics of thermally modified wood are usually provided in a very limited way, and there is no information on specific heat in particular. An original calorimetric method was used to determine the specific heat of untreated and thermally modified European beech wood (Fagus sylvatica L.). The inverse modeling was implemented to estimate the anisotropic thermal conductivity, and significant differences were found for the radial and tangential directions. The thermal modification highly influenced the increase in the thermal conductivity in the longitudinal direction. The validation procedure showed credibility of the applied methods, and it is clear that modeling of heat transfer in thermally modified wood leads to erroneous results when using thermal properties determined merely for untreated wood.

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“…Endo et al (2016) also report similar effects of heating at intermediate humidities, but in this case, the reduced EMC was largely recovered by moistening the wood in saturated water vapor at 25C. This temporary reduction in hygroscopicity is explained by the annealing-like physical aging of amorphous wood polymers, and is probably responsible for the unstable moisture sorption characteristics of dry-heated wood under cyclic changes in humidity (Majka et al 2016).…”

Section: Introductionmentioning

confidence: 69%

Reversible and irreversible dimensional changes of heat-treated wood during alternate wetting and drying

Obataya

Higashihara

2017

Wood Sci Technol

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Spruce wood specimens were heat-treated in saturated water vapor (steaming) and in the absence of moisture (dry heating) at 120-180C, and their wet volumes were measured during alternate wetting and drying cycles. After the first wetting and drying cycle, the wet volume of steamed wood decreased, and then remained unchanged during the following alternate wetting and drying cycles. The wet volume regained its initial level when soaked in dimethyl sulfoxide (DMSO), followed by washing in water, but decreased again after subsequent drying and rewetting. Such reversible changes were not observed in unheated and dry-heated specimens. This suggested a hydrophobic structure formed during drying or plastic expansion of cell lumen due to steaming and soaking in DMSO. Although heat treatments reduced the hygroscopicity of the wood, steamed wood showed more swelling, i.e., lower dimensional stability than unheated and dry-heated wood. This is probably because steaming caused serious degradation of cell wall components, therefore loosening its fiber-reinforced structure restricting the swelling of the cell wall. When wood is exposed to alternate wetting and drying, steaming is not advisable because it may reduce the dimensional stability of the wood.

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Effects of Cyclic Changes in Relative Humidity on the Sorption Hysteresis of Thermally Modified Spruce Wood

Cited by 28 publications

References 20 publications

Sorption and Surface Energy Properties of Thermally Modified Spruce Wood Components

Sorption and Surface Energy Properties of Thermally Modified Spruce Wood Components

Effects of heat treatment on thermal properties of European beech wood

Reversible and irreversible dimensional changes of heat-treated wood during alternate wetting and drying

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