All wood in growing trees contains a considerable amount of water which is commonly called sap. Water is contained in wood as either bound water or free water. The bound water is held within cell walls by bonding forces between water and cellulose molecules, while the free water is contained in the cell cavities and is not held by these forces. The amount of water in wood can be calculated and expressed as a percent of the dry weight is called the “Moisture Content” (MC). The hygroscopic nature of wood cause the water movement, either along the grain or across the grain. The free water moves through cell cavities (along the grain) and pit openings (across the grain). During drying it is moved by capillary forces that exert a pull on the free
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For bound water moves as vapor through empty cell cavities (along the grain) and pit openings (across the grain) as well as directly through cell walls (across the grain). Water movement along the grain is many times faster than across the grain. The MC in living trees (green MC) varies by species Differences between sapwood and heartwood also exist for hardwoods and softwoods. Hardwoods exhibit no green MC pattern between heart-wood and sapwood, species variation is extremely wide. Softwoods commonly have a heartwood MC near the FSP which is much lower than the MC of its sapwood. Next, The Fiber Saturation Point (FSP) is the point at which there is no free water present in the cell lumens and there is the maximum amount of bound water present in the cell walls. Generally FSP considered as 30%. Once wood has been dried below the FSP, it seldom regains any free water that would increase the MC above that point. The wood loses or gains bound water until the amount it contains is in balance with that of the surrounding atmosphere. The amount of water at this point of balance is called the equilibrium moisture content (EMC), and is always below 30 percent. But, The EMC depends on temperature and …show more content…
After, we remove more and more water, the wood get stronger at an exponential rate and shrink at a lineal rate. If we add more and more water, the wood will lose strength and swell until the FSP is reached then nothing more happens. Wood is an anisotropic material, which is an anisotropic means that its structure and properties vary in different directional axes: R (radial), T (tangential), and L (longitudinal). The shrinkage and swelling of wood is different for each axes. In general, the amount of shrinking and swelling which takes place is directly proportional to moisture content changes in the wood. Wood shrinks and swells the greatest amount in the tangential direction, about half as much in the radial direction, and about 0.1% to 0.2% in the longitudinal direction. The amounts of shrinkage which various species undergo as they are dried from the green to oven-dry condition may be found from the shrinkage coefficients (SC). Sugar maple, for example shrinks 9.5 percent in the tangential direction as it goes from the green to the oven dry condition and 4.9 percent in the radial direction. Differences in shrinkage between species may be significant. In contrast to sugar maple, mahogany shrinks 5.0% and 3.6% in the tangential and radial directions, respectively. It is this difference between shrinking in the radial and tangential directions that causes splits to develop in
For bound water moves as vapor through empty cell cavities (along the grain) and pit openings (across the grain) as well as directly through cell walls (across the grain). Water movement along the grain is many times faster than across the grain. The MC in living trees (green MC) varies by species Differences between sapwood and heartwood also exist for hardwoods and softwoods. Hardwoods exhibit no green MC pattern between heart-wood and sapwood, species variation is extremely wide. Softwoods commonly have a heartwood MC near the FSP which is much lower than the MC of its sapwood. Next, The Fiber Saturation Point (FSP) is the point at which there is no free water present in the cell lumens and there is the maximum amount of bound water present in the cell walls. Generally FSP considered as 30%. Once wood has been dried below the FSP, it seldom regains any free water that would increase the MC above that point. The wood loses or gains bound water until the amount it contains is in balance with that of the surrounding atmosphere. The amount of water at this point of balance is called the equilibrium moisture content (EMC), and is always below 30 percent. But, The EMC depends on temperature and …show more content…
After, we remove more and more water, the wood get stronger at an exponential rate and shrink at a lineal rate. If we add more and more water, the wood will lose strength and swell until the FSP is reached then nothing more happens. Wood is an anisotropic material, which is an anisotropic means that its structure and properties vary in different directional axes: R (radial), T (tangential), and L (longitudinal). The shrinkage and swelling of wood is different for each axes. In general, the amount of shrinking and swelling which takes place is directly proportional to moisture content changes in the wood. Wood shrinks and swells the greatest amount in the tangential direction, about half as much in the radial direction, and about 0.1% to 0.2% in the longitudinal direction. The amounts of shrinkage which various species undergo as they are dried from the green to oven-dry condition may be found from the shrinkage coefficients (SC). Sugar maple, for example shrinks 9.5 percent in the tangential direction as it goes from the green to the oven dry condition and 4.9 percent in the radial direction. Differences in shrinkage between species may be significant. In contrast to sugar maple, mahogany shrinks 5.0% and 3.6% in the tangential and radial directions, respectively. It is this difference between shrinking in the radial and tangential directions that causes splits to develop in