Wood and Moisture | The Wood Database
The moisture content of wood means the relationship between the mass of water in it and the mass of the timber without the water. (For example, if a piece of. These microfibrils form the major structural component in cell walls and play an important role in the wood-moisture relationship. Amount of water in wood. Due to a lapse in federal funding, this USDA website will not be actively updated. Once funding has been reestablished, online operations will continue.
Equilibrium moisture content - Wikipedia
It stays as it is as long as the relative humidity and temperature of the surroundings are not changed. What Is Relative Humidity? Temperature and air pressure affect the relative humidity of the air. The following equation is generally used to calculate the relative humidity of air: Therefore, EMC can be plotted as a function of relative humidity.
What Is Equilibrium Moisture Content? Plus: What It Means for Wood
The EMC values of solid wood are generally greater than wood composites. For a reasonable estimation of the true target EMC at any value of relative humidity and temperature, the following equation may be used: Coastal areas like Miami, Seattle, and Japan have higher values of relative humidity and subsequently higher values of EMCs than non-coastal areas.
The moisture content of a piece of wood at a particular time determines how wet or dry that piece of wood is. The lower the moisture content, the more dried the wood and vice versa. It should be noted that in real-world situations, the FSP is never uniformly reached throughout the thickness of a piece of lumber. A moisture gradient develops where the outside shell is drier, with the interior core still wet and playing catch-up.Moisture Content from the Manufacturer to the End User
As the MC of wood drops below the FSP, it will continue to lose moisture until it eventually stabilizes at a value that is commensurate with the surrounding moisture in the air. This is known as the point of equilibrium moisture content, or simply EMC.
The EMC will change based upon the fluctuating temperature and relative humidity of the surrounding air.
In addition to the fundamental fact that wood is hygroscopic, perhaps the most crucial concept to understand regarding wood and moisture is the link between relative humidity and equilibrium moisture content.
From studying the included chart, several important points pertaining to the relationship between relative humidity RH and equilibrium moisture content EMC emerge. Humidity changes that happen in this window have a slightly gentler effect on EMC, and hence results in smaller amounts of shrinking and swelling.
It can be very useful to make mental notes of common humidity levels and their corresponding EMC.
Moisture Relations and Physical Properties of Wood - Semantic Scholar
Wood shrinks or swells as its moisture content changes, but only when water is taken up or given off from the cell walls. Any change in water content in the cell cavity will have no effect on the dimension of the wood. Therefore, wood only shrinks and swells when it changes moisture content below the point of fiber saturation.
Like other hygroscopic materials, wood placed in an environment with stable temperature and relative humidity will eventually reach a moisture content that yields no vapor pressure difference between the wood and the surrounding air.
Equilibrium moisture content
When the indoor air is very dry, wood will release moisture. When the indoor air is too humid, wood will absorb moisture.
This natural behaviour of wood is responsible for some of the problems sometimes encountered when wood dries. As the piece dries, it develops a moisture gradient across its section dry on the outside, wet on the inside. The dry outer shell wants to shrink as it dries below fiber saturation, however, the wetter core constrains the shell. This can cause checks to form on the surface.