Abstract
The degree with which wood shrinks and swells with changing moisture content is an important property which determines its suitability for different applications. This property, known as dimensional stability, is often a target property for improvement in wood modification research. Its importance makes it a commonly quantified wood property. Despite this, methods for measuring dimensional stability are not standardised, and there is little consensus on appropriate test methods. Dimensional stability tests can be classified according to the method used to change the moisture content of the wood (liquid water or water vapour) and the duration of the test (until equilibrium is reached, or a shorter duration). Each class of test represents a situation that wood products may encounter in service, and different types of wood (modified or otherwise) may respond differently to each situation. This means that comparative performance between different wood types may be dependent on the test used (and may not be valid for some situations encountered in service). In this paper, standard test methods and methods described in the literature are compared, and recommendations are given for selecting an appropriate dimensional stability test and for minimising sources of bias and measurement uncertainty in the test. It is expected that this will also encourage the adoption of more standardised test methods, enabling comparisons to be made between different studies and different wood types.
Highlights
Dimensional stability affects how a final wood product will move and distort in service and is an important wood property to understand
Almeida and Hernández [17] and Naderi and Hernández [18] found that resaturating dried blocks of beech (Fagus grandifolia Ehrh.) or sugar maple (Acer saccharum Marsh.) by immediately placing dried blocks in water produced more swelling than for a less severe method, where samples were equilibrated to high moisture contents before resaturation
Sargent et al [2] found that modified wood samples continued to increase in dimension for up to 48 h when soaking in water after vacuum-pressure resaturation
Summary
Dimensional stability affects how a final wood product will move and distort in service and is an important wood property to understand. This is true in wood modification research and among processers of modified wood products, where the modification processes often aim to improve dimensional stability. The concept of dimensional stability is not always well defined, and there are numerous methods used to measure dimensional stability, with little consensus on test methods or metrics used. In this paper, ‘stability’ refers to dimensional stability—the amount a piece of wood shrinks or swells in response to a change in its moisture content, or a change in moisture in its environment. Many method variations will still yield similar results, but some methods compromise the properties being measured, potentially giving misleading results
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