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

Thybring, Emil Engelund; Kymäläinen, Maija; Rautkari, Lauri

doi:10.1007/s00226-017-0977-7

Cited by 64 publications

(37 citation statements)

References 182 publications

(259 reference statements)

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“…Today, sorption measurements are most commonly done gravimetrically, as has been done for more than 500 years [12]. Gravimetric methods for water vapor sorption in wood have been broadly reviewed previously [4]. This article focuses on methods most relevant to sorption kinetics.…”

Section: Overview Of Experimental Methods For Determining Sorption Kimentioning

confidence: 99%

“…It should be noted that in much of the wood science literature, the absorption of water vapor is often referred to as "adsorption". However, given the IUPAC (International Union of Pure and Applied Chemistry) definitions for these terms, the sorption process in wood, whereby water molecules are taken up in the bulk of the cell walls and in the capillary structure, most closely resembles absorption, whereas, adsorption strictly refers to processes at an interface [4].…”

Section: Introductionmentioning

confidence: 99%

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Kinetics of Water Vapor Sorption in Wood Cell Walls: State of the Art and Research Needs

Thybring

Glass

Zelinka

2019

Forests

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Water vapor sorption is the most fundamental aspect of wood-moisture relations. It is directly or indirectly related to the physical properties of wood and the onset of wood-damage mechanisms. While sorption properties of cellulosic materials have been utilized since antiquity, the time-dependent transition from one moisture content to another (i.e., sorption kinetics) has received much less attention. In this critical review, we present the state-of-the-art of water vapor sorption kinetics in wood. We first examine different experimental methods that have been used to measure sorption kinetics, from the quartz helix vacuum balance beginning in earnest in the 1930s, to automated sorption balances used recently. We then give an overview of experimental observations and describe the physical phenomena that occur during the sorption process, which potentially govern the following kinetics: boundary layer mass transfer resistance, heat of sorption, cell wall diffusion, swelling, and polymer mobility. Finally, we evaluate theoretical models that have been proposed for describing sorption kinetics, considering both experimental data and the physical processes described in the previous section. It is clear that no previously developed model can phenomenologically describe the sorption process. Instead, new models are needed. We conclude that the development of new models will require more than simple gravimetric measurements. In addition to mass changes, complementary techniques are needed to probe other important physical quantities on multiple length scales.

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Section: Overview Of Experimental Methods For Determining Sorption Kimentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Kinetics of Water Vapor Sorption in Wood Cell Walls: State of the Art and Research Needs

Thybring

Glass

Zelinka

2019

Forests

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“…In order to have probe solution with narrow size distributions, PEG6k was acquired as reference standard from U.S. Pharmacopeia (USP, Rockville, MD, USA), while PEK40k and PEG108k were acquired as analytical standards for gel permeation chromatography from Sigma Aldrich (Darmstadt, Germany). Molecular sizes are according to regression of hydrodynamic diameter (d) with the molar mass (M n ) by [36]. The initial concentration of each probe molecule was 0.6% w/w.…”

Section: Determination Of Cell Wall Moisture Content With Solute Exclmentioning

confidence: 99%

How much water can wood cell walls hold? A triangulation approach to determine the maximum cell wall moisture content

et al. 2020

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Wood is a porous, hygroscopic material with engineering properties that depend significantly on the amount of water (moisture) in the material. Water in wood can be present in both cell walls and the porous void-structure of the material, but it is only water in cell walls that affects the engineering properties. An important characteristic of wood is therefore the capacity for water of its solid cell walls, i.e. the maximum cell wall moisture content. However, this quantity is not straightforward to determine experimentally, and the measured value may depend on the experimental technique used. In this study, we used a triangulation approach to determine the maximum cell wall moisture content by using three experimental techniques based on different measurement principles: low-field nuclear magnetic resonance (LFNMR) relaxometry, differential scanning calorimetry (DSC), and the solute exclusion technique (SET). The LFNMR data were furthermore analysed by two varieties of exponential decay analysis. These techniques were used to determine the maximum cell wall moisture contents of nine different wood species, covering a wide range of densities. The results from statistical analysis showed that LFNMR yielded lower cell wall moisture contents than DSC and SET, which were fairly similar. Both of the latter methods include factors that could either underestimate or overestimate the measured cell wall moisture content. Because of this and the fact that the DSC and SET methods are based on different measurement principles, it is likely that they provide realistic values of the cell wall moisture content in the water-saturated state.

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“…Also, the degree of polarity and hydrogen bonding capability of the probe molecule will affect the result [114]. Furthermore, solute exclusion studies of wood vary widely in the amount of time allotted for the samples to come to equilibrium with the probe solution [115]. Only "several minutes" were used for pulp samples [20] while solid wood samples were equilibrated for 1-14 days [110,111,116].…”

Section: Nanopore Blockingmentioning

confidence: 99%

The Importance of Moisture for Brown Rot Degradation of Modified Wood: A Critical Discussion

Ringman

Beck

Pilgård

2019

Forests

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The effect of wood modification on wood-water interactions in modified wood is poorly understood, even though water is a critical factor in fungal wood degradation. A previous review suggested that decay resistance in modified wood is caused by a reduced wood moisture content (MC) that inhibits the diffusion of oxidative fungal metabolites. It has been reported that a MC below 23%–25% will protect wood from decay, which correlates with the weight percent gain (WPG) level seen to inhibit decay in modified wood for several different kinds of wood modifications. In this review, the focus is on the role of water in brown rot decay of chemically and thermally modified wood. The study synthesizes recent advances in the inhibition of decay and the effects of wood modification on the MC and moisture relationships in modified wood. We discuss three potential mechanisms for diffusion inhibition in modified wood: (i) nanopore blocking; (ii) capillary condensation in nanopores; and (iii) plasticization of hemicelluloses. The nanopore blocking theory works well with cell wall bulking and crosslinking modifications, but it seems less applicable to thermal modification, which may increase nanoporosity. Preventing the formation of capillary water in nanopores also explains cell wall bulking modification well. However, the possibility of increased nanoporosity in thermally modified wood and increased wood-water surface tension for 1.3-dimethylol-4.5-dihydroxyethyleneurea (DMDHEU) modification complicate the interpretation of this theory for these modifications. Inhibition of hemicellulose plasticization fits well with diffusion prevention in acetylated, DMDHEU and thermally modified wood, but plasticity in furfurylated wood may be increased. We also point out that the different mechanisms are not mutually exclusive, and it may be the case that they all play some role to varying degrees for each modification. Furthermore, we highlight recent work which shows that brown rot fungi will eventually degrade modified wood materials, even at high treatment levels. The herein reviewed literature suggests that the modification itself may initially be degraded, followed by an increase in wood cell wall MC to a level where chemical transport is possible.

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

Cited by 64 publications

References 182 publications

Kinetics of Water Vapor Sorption in Wood Cell Walls: State of the Art and Research Needs

Kinetics of Water Vapor Sorption in Wood Cell Walls: State of the Art and Research Needs

How much water can wood cell walls hold? A triangulation approach to determine the maximum cell wall moisture content

The Importance of Moisture for Brown Rot Degradation of Modified Wood: A Critical Discussion

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