Fiber saturation

At equihbrium with relative humidity below 100%, the moisture ia wood is present primarily ia the cell wads. The moisture content at which the ceU wads would be saturated and the ced cavities empty is caded the fiber saturation poiat. Actuady, such distribution is impossible. Beginning at - 90% relative humidity, some condensation may occur ia smad capidaries. The determination of the fiber saturation poiat is based on the fact that certain properties of wood (eg, strength and volume) change uniformly at first with increasing moisture content and then become iadependent of the moisture content (Fig. 2). The equdibrium moisture content (usuady determined by extrapolation), at which the property becomes constant at 25 to 30% moisture, is represented by the fiber saturation poiat. 

Fiber saturation point is the bound moisture content of ceUular materials such as wood. 

In porous and granular materials, Hquid movement occurs by capillarity and gravity, provided passages are continuous. Capillary flow depends on the hquid material s wetting property and surface tension. Capillarity appHes to Hquids that are not adsorbed on capillary walls, moisture content greater than fiber saturation in cellular materials, saturated Hquids in soluble materials, and all moisture in nonhygroscopic materials. 

Fiber-saturation point is the moisture content of celhilar materials (e.g., wood) at which the cell walls are completely saturated while the cavities are liquid-free. It may be defined as the equihbrium moisture content as the humidity of the surrounding atmosphere approaches saturation. 

Capillary Flow Moisture which is held in the interstices of solids, as liquid on the surface, or as free moisture in cell cavities, moves by gravity and capiUarity, provided that passageways for continuous flow are present. In diying, liquid flow resulting from capiUarity appUes to liquids not held in solution and to aU moisture above the fiber-saturation point, as in textiles, paper, and leather, and to all moisture above the equiUbrium moisture content at atmospheric saturations, as in fine powders and granular solids, such as paint pigments, minerals, clays, soU, and sand. 

FIGURE 68 Wooden bowl. A wooden bowl made of boxwood, first century c.e., from Qumran, Israel the wood used to make the bowl seems to have been imported from Turkey. The excellent preservation of the bowl is due to extremely hot and dry environmental conditions in the region. Three conditions are necessary for wood to decay (1) a favorable temperature (0-32°C), (2) moisture in excess of the fiber saturation point (above 25-30%) and (3) an adequate supply of oxygen. If any one of these is eliminated wood remains well preserved for long periods of time. 

Liger-Belair, G., Topgaard, D., Voisin, C., and Jeandet, P. (2004). Is the wall of a cellulose fiber saturated with liquid whether or not permeable with CO2 dissolved molecules Application to bubble nucleation in champagne wines. Langmuir 20,4132- 138. 

Microfibers. PAC microfibers (single titer less than 1 dtex) behave differently in some respects from normal acrylic fibers [171], First, more dye is required for the desired shade in each case because of the greater light scattering of the fiber. This requirement increases more than twofold with increasing depth of color (similar to pore fibers). For this reason, the fiber saturation is usually adjusted to a higher value by the fiber producer. The characteristic dyeing rate of the fiber is... 

It is very difficult to restrict the oxygen from microorganisms so control measures based on this approach would probably be fruitless. Wood below the fiber saturation point does not decay. Therefore, by restricting the amount of water in the wood cell wall below the fiber saturation point, the microorganisms will not thrive. 

Specific Heat. The specific heat of textiles, particularly wool, has been the subject of recent investigations. For moisture contents above the fiber saturation point of wool, reduced, supercontracted, and chemically modified wool fabrics exhibited endothermic peaks at -30 to 0°C that resulted from the heat of fusion of absorbed water. In that temperature range, a significant increase in the specific heat of the wool fabrics was also... 

To help determine which basic dyes can be combined for shade matching, key dyebath parameters have been developed.16 The first parameter pertains to the dyes themselves and is known as the combinability constant (k). This value provides a measure of how fast a basic dye will dye the fiber, and the dyes are rated on a scale of 1 (fast) to 5 (slow). The second parameter pertains to the fiber type involved and is known as the fiber saturation value (SF). This value provides an indication... 

The fiber saturation point (FSP) of cotton is the total amount of water present within the cell wall expressed as a ratio of water to solid content. It is equivalent to the water of imbibition of the fiber, also called its water retention value. The FSP has been measured using solute exclusion, centrifugation, porous plate, and hydrostatic tension techniques. It occurs at RVP greater than 0.997 and from the review of the papers, it has been concluded that the studies have yielded a value for FSP in the range of 0.43 to 0.52 g/g [303]. 

Changes in the moisture content of the wood cell wall have a major effect on the mechanical properties of wood [5]. At moisture contents from oven-dry (OD) to the fiber saturation point (FSP), water accumulates in the wood cell wall (bound water). Above the FSP, water accumulates in the wood cell cavity (free water) and there is no tangible strength effect associated with a change in free water content. However, at moisture contents between OD and the FSP, water does affect strength. Increased amounts of bound water interfere with and reduce hydrogen bonding between the polymers of the cell... 

Table 4 Fiber Saturation Point of Control and Acetylated Aspen Flakes...

Weight percent gain Fiber saturation point... 

Wood is subject to water iafiltration by both Hquid and vapor. As the moisture content iacreases, the wood wiU sweU imtU it reaches its maximum dimension at its fiber-saturation point (about 30% moisture). Variation in the bound water content between zero and 30% wfll aUow the wood to shrink and sweU. Rapid dimensional changes resulting from changes in the level of bound water cause the wood to crack and spHt. These cracks wfll then aUow moisture to absorb easily and quicldy into the wood. At moisture content levels above the fiber-saturation point, moisture wfll be present as free water, which in turn promotes the rate of wood decay. 

As a consequence of its hydrophilicity, wood tissue will seek to maintain, through either gain or loss of moisture, an equilibrium moisture content with the surrounding atmosphere. If the wood takes on water, the cell walls proceed to swell until the cell walls become water-saturated. The latter moisture content is called the wood s fiber saturation point. In contrast, loss of wood water (below the fiber saturation point), due to diffusion and evaporation, results in wood shrinkage. 

The water content of the wood cell wall has a strong influence on the wood s mechanical properties, and a higher moisture content, at least below the fiber saturation point, and normally is inversely related to most strength properties see Chapter 5). This situation is easily reconciled if one considers that the takeup of water below the... 

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