The water vapor sorption mechanism and its hysteresis in wood: the water/void mixture postulate

Willems, Wim

doi:10.1007/s00226-014-0617-4

Cited by 43 publications

(28 citation statements)

References 33 publications

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“…The removal of cell wall carbohydrates by hydrolysis and the subsequent water leaching should lead to a reduction in the number of OH groups as polar sites for water. Since the removed carbohydrates are most likely those that feature the highest polymer mobility and reactivity (Borrega and Kärenlampi 2008), accessible OH groups should be preferentially eliminated (Willems 2014). However, the slope at which EMC decreased as a function of ML c was higher for oven-dry samples than for water- saturated samples.…”

Section: Maximum Swelling and Hygroscopicity Tested On Solid Samplesmentioning

confidence: 92%

“…Nevertheless, it should be noted that excessive matrix stiffening, which may be achieved in high-temperature, low water vapor pressure environments, limits the accessibility of sorption sites upon wood swelling or softening almost completely (Willems 2014(Willems , 2015, but may also decrease the relaxation of stresses applied by external loads considerably (González-Pena et al 2005). The latter causes a brittle behavior with abrupt wood failures as a result of localized stresses.…”

Section: Hygroscopicity Tested On Wood Particlesmentioning

confidence: 99%

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Wood moisture content during the thermal modification process affects the improvement in hygroscopicity of Scots pine sapwood

2016

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Elevated wood moisture contents during the thermal modification process have been shown to adversely affect the improvement in dimensional stability and hygroscopicity. This study tested the hypothesis that the effect of elevated wood moisture content is based on the impact of water on chemical reactions which determine the cell wall matrix stiffness. Samples of Scots pine sapwood (Pinus sylvestris L.) were thermally modified in saturated water vapor at different peak temperatures and durations starting either in oven-dry or in water-saturated state. For a given mass loss caused by the modification process, the improvement in maximum swelling and equilibrium moisture content was stronger for oven-dry samples. After removal of water-soluble degradation products, which caused a cell wall bulking effect, the maximum swelling even increased after modification in water-saturated state. Based on dynamic vapor sorption measurements, it was evidenced that the modification in oven-dry state increased the cell wall matrix stiffness which improved dimensional stability and hygroscopicity. Enhanced bond formation in the polymeric network, i.e., via condensation and cross-linking reactions during the treatment of oven-dry wood, is suggested as a cause for this increase in matrix stiffness. In contrast, the modification in water-saturated state enhanced the flexibility of the cell wall matrix, which increased the cell wall swelling and limited the improvement of hygroscopicity to the reduction in OH groups by removal of hemicelluloses. This enhanced matrix flexibility was potentially caused by predominant hydrolytic cleavage of bonds in case of water-

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Section: Maximum Swelling and Hygroscopicity Tested On Solid Samplesmentioning

confidence: 92%

Section: Hygroscopicity Tested On Wood Particlesmentioning

confidence: 99%

Wood moisture content during the thermal modification process affects the improvement in hygroscopicity of Scots pine sapwood

2016

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“…Wood-water relations have been widely studied in the last century (Engelund et al 2013;Willems 2014), although few studies have addressed the sorption of juvenile and mature wood (Lenth and Kamke 2001;Militz et al 2003;Neimsuwan et al 2008;Hill et al 2011) and none have compared the thermodynamic properties of juvenile and mature wood of the same species through the sorption isotherms. Knowing the hygroscopic response of juvenile and mature wood through the sorption isotherms and using the isotherms to determine the thermodynamic properties of each type of wood can be particularly important to improve energy performance in industrial processes such as drying technology.…”

Section: Introductionmentioning

confidence: 99%

Juvenile and mature wood of Abies pinsapo Boissier: sorption and thermodynamic properties

et al. 2015

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For industrial processes, it is important to study the hygroscopicity and thermodynamic properties of juvenile and mature wood. Samples of Abies pinsapo Boiss. collected in the natural areas of the species in Spain were used to study these properties in both types of wood. The equilibrium moisture contents were obtained, and the 15, 35 and 50°C isotherms were plotted following the Guggenheim-Anderson-Boer-Dent model. The thermodynamic parameters were calculated using the integration method of the Clausius-Clapeyron equation. Chemical analyses, infrared spectra and X-ray diffractograms were applied to assess chemical modifications and possible changes in the cell wall structure. The chemical composition of the mature wood shows a decrease in the lignin and hemicelluloses content and an increase in the extracts and a-cellulose. The sorption isotherms for the three temperatures studied are higher in the mature wood than in the juvenile wood. Causes of this include the higher content of a-cellulose, the higher crystallinity index and the shorter crystallite length in the mature wood. No difference was found between the juvenile and mature wood in relation to the point of inflexion where the multilayer starts to predominate over the monolayer (approximately 30 %). In terms of the thermodynamic properties, the heat involved is greater in desorption than in adsorption, and more heat is involved in the mature wood than in the juvenile wood.

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“…And the multilayer sorption isotherm model (e.g. Hailwood & Horrobin model) enjoys the most popularity since its ability to make accurate fits in experimental data [20], although recent sorption sites occupancy theory has brought about some evidences that raise doubts on its realistic physical fundamentals [6,20,21]. The drawback of these multilayer sorption models is the inconsistency with the thermodynamic aspects of sorption [22,23].…”

Section: Sorption Isotherm Models and Fitting Methodsmentioning

confidence: 99%

Evaluation of moisture sorption models and modified Mualem model for prediction of desorption isotherm for wood materials

Zhang

Zillig

Künzel

et al. 2015

Building and Environment

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The water vapor sorption mechanism and its hysteresis in wood: the water/void mixture postulate

Cited by 43 publications

References 33 publications

Wood moisture content during the thermal modification process affects the improvement in hygroscopicity of Scots pine sapwood

Wood moisture content during the thermal modification process affects the improvement in hygroscopicity of Scots pine sapwood

Juvenile and mature wood of Abies pinsapo Boissier: sorption and thermodynamic properties

Evaluation of moisture sorption models and modified Mualem model for prediction of desorption isotherm for wood materials

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