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Phytopathology Peterson MD, Thomas RJ Protection of wood from decay fungi by acetylation - an ultrastructural and chemical study. International Biodeterioration and Biodegradation 86 Part B: International Wood Products Journal 8: Schmidt O Indoor wood-decay basidiomycetes: damage, causal fungi, physiology, identification and characterization, prevention and control. Mycological Progress 6: Holztechnologie Srebotnik E, Messner K, Foisner R Penetrability of white rot-degraded pine wood by the lignin peroxidase of Phanerochaete chrysosporium. Swelling in water and fiber saturation point.

Tappi Takahashi M, Imamura Y, Tanahashi M Effect of acetylation on decay resistance of wood against brown-rot, white-rot and soft-rot fungi. Lappeenranta Finland May Thybring EE The decay resistance of modified wood influenced by moisture exclusion and swelling reduction. Thybring EE Water relations in untreated and modified wood under brown-rot and white-rot decay.

Part I: Results for untreated, acetylated, and furfurylated Norway spruce. Science Viitanen H, Ritschkoff AC Brown rot decay in wooden constructions - effect of temperature, humidity and moisture. Viitanen HA Modelling the time factor in the development of brown rot decay in pine and spruce sapwood - the effect of critical humidity and temperature conditions.

Wood-water relations - Ghent University Library

Fr [Water balance and matter transport in Merulius lacrymans Wulf. Welzbacher CR, Rapp AO Durability of thermally modified timber from industrial-scale processes in different use classes: Results from laboratory and field tests. Williams FC, Hale MD The resistance of wood chemically modified with isocyanates: the role of moisture content in decay suppression. Xu G, Goodell B Mechanisms of wood degradation by brown-rot fungi: chelator-mediated cellulose degradation and binding of iron by cellulose. Journal of Testing and Evaluation Wood Material Science and Engineering International Wood Products Journal 7: Zeller SM Humidity in relation to moisture imbibition by wood and to spore germination on wood.

Annals of the Missouri Botanical Garden 7: Related Content. Changes in moisture exclusion efficiency and crystallinity of thermally modified wood with aging Tarmian A, Mastouri A Vol. Behavior of pubescent oak Quercus pubescens Willd.

How to Correct Wood Moisture Content

Page Contents Page Top. More on this topic: Wood modification and environmental impact assessment in research Kinetic analysis of thermal modified poplar wood VOC emission profile of different wood species during moisture cycles Changes in thermally modified wood with aging Wood modification technologies More Google scholar. Download Reference.

Wood-water relations

RIS Zotero. Nature and Landscape Conservation. The drying of wood is thus an area for research and development, which concern many researchers and timber companies around the world. Water in wood normally moves from zones of higher to zones of lower moisture content Walker et al. Drying starts from the exterior of the wood and moves towards the centre, and drying at the outside is also necessary to expel moisture from the inner zones of the wood. Wood subsequently attains equilibrium with the surrounding air in moisture content.


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The driving force of moisture movement is chemical potential. However, it is not always easy to relate chemical potential in wood to commonly observable variables, such as temperature and moisture content Keey et al. Moisture in wood moves within the wood as liquid or vapour through several types of passageways, based on the nature of the driving force, e. These pathways consist of cavities of the vessels, fibres, ray cells, pit chambers and their pit membrane openings, intercellular spaces and transitory cell wall passageways.

Movement of water takes place in these passageways in any direction, longitudinally in the cells, as well as laterally from cell to cell until it reaches the lateral drying surfaces of the wood. The higher longitudinal permeability of sapwood of hardwood is generally caused by the presence of vessels.

Wood-water relations

The lateral permeability and transverse flow is often very low in hardwoods. The presence of gum veins, the formation of which is often a result of natural protective response of trees to injury, is commonly observed on the surface of sawn boards of most eucalypts.

The available space for air and moisture in wood depends on the density and porosity of wood. Porosity is the volume fraction of void space in a solid. The porosity is reported to be 1. On the other hand, permeability is a measure of the ease with which fluids are transported through a porous solid under the influence of some driving forces, e.

It is clear that solids must be porous to be permeable, but it does not necessarily follow that all porous bodies are permeable. Permeability can only exist if the void spaces are interconnected by openings. For example, a hardwood may be permeable because there is intervessel pitting with openings in the membranes Keey et al. If these membranes are occluded or encrusted, or if the pits are aspirated, the wood assumes a closed-cell structure and may be virtually impermeable. The density is also important for impermeable hardwoods because more cell-wall material is traversed per unit distance, which offers increased resistance to diffusion Keey et al.

Hence lighter woods, in general, dry more rapidly than do the heavier woods. The transport of fluids is often bulk flow momentum transfer for permeable softwoods at high temperature while diffusion occurs for impermeable hardwoods Siau, These mechanisms are discussed below. Three main driving forces used in different version of diffusion models are moisture content, the partial pressure of water vapour, and the chemical potential Skaar, ; Keey et al.

These are discussed here, including capillary action, which is a mechanism for free water transport in permeable softwoods.


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Total pressure difference is the driving force during wood vacuum drying. Capillary forces determine the movements or absence of movement of free water. It is due to both adhesion and cohesion. Adhesion is the attraction between water to other substances and cohesion is the attraction of the molecules in water to each other. As wood dries, evaporation of water from the surface sets up capillary forces that exert a pull on the free water in the zones of wood beneath the surfaces.

When there is no longer any free water in the wood capillary forces are no longer of importance. The chemical potential is explained here since it is the true driving force for the transport of water in both liquid and vapour phases in wood Siau, The Gibbs free energy per mole of substance is usually expressed as the chemical potential Skaar, The chemical potential of unsaturated air or wood below the fibre saturation point influences the drying of wood.


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Equilibrium will occur at the equilibrium moisture content as defined earlier of wood when the chemical potential of the wood becomes equal to that of the surrounding air. The chemical potential of sorbed water is a function of wood moisture content. Therefore, a gradient of wood moisture content between surface and centre , or more specifically of activity, is accompanied by a gradient of chemical potential under isothermal conditions. Moisture will redistribute itself throughout the wood until the chemical potential is uniform throughout, resulting in a zero potential gradient at equilibrium Skaar, The flux of moisture attempting to achieve the equilibrium state is assumed to be proportional to the difference in chemical potential, and inversely proportional to the path length over which the potential difference acts Keey et al.

The gradient in chemical potential is related to the moisture content gradient as explained in above equations Keey et al. The diffusion model using moisture content gradient as a driving force was applied successfully by Wu and Doe et al. Though the agreement between the moisture-content profiles predicted by the diffusion model based on moisture-content gradients is better at lower moisture contents than at higher ones, there is no evidence to suggest that there are significantly different moisture-transport mechanisms operating at higher moisture contents for this timber.

Their observations are consistent with a transport process that is driven by the total concentration of water.

Wood-Water Relations

The diffusion model is used for this thesis based on this empirical evidence that the moisture-content gradient is a driving force for drying this type of impermeable timber. Differences in moisture content between the surface and the centre gradient, the chemical potential difference between interface and bulk move the bound water through the small passageways in the cell wall by diffusion.

In comparison with capillary movement, diffusion is a slow process. Diffusion is the generally suggested mechanism for the drying of impermeable hardwoods Keey et al. Furthermore, moisture migrates slowly due to the fact that extractives plug the small cell wall openings in the heartwood.

Introduction

This is why sapwood generally dries faster than heartwood under the same drying conditions. Radial diffusion is somewhat faster than tangential diffusion. Although longitudinal diffusion is most rapid, it is of practical importance only when short pieces are dried. Generally the timber boards are much longer than in width or thickness. If the boards are quartersawn, then the width will be in the radial direction whereas the thickness will be in tangential direction, and vice versa for plain-sawn boards.

Most of the moisture is removed from wood by lateral movement during drying. The chief difficulty experienced in the drying of timber is the tendency of its outer layers to dry out more rapidly than the interior ones.