Fiber-saturation point measurement

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. 

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]. 

At the cellular level, the true density of dry cell wall substance (i.e., within the cell wall) has been determined to be about 1.5 g/ cm, varying to some extent with the method of measurement and species (2). There are voids within the dry wood cell wall, but the void volume here (i.e., micropores) is reported to be only about 2-4%. However, this figure would be expected to increase as wood moisture content is increased to the fiber saturation point (28). 

When wood below the fiber-saturation point interacts with water, heat is evolved, and there are changes in the free energy and entropy of the sorbed water. Furthermore, the wood exerts swelling forces that can be measured. These effects can be treated by classical thermodynamic methods although moisture sorption by wood is not a perfectly reversible process because sorption hysteresis is involved, as was pointed out in the section on Moisture Sorption Isotherms (p. 136). 

Various terms have been used to characterize the water associated with cellulose fibers. Bound water, imbibed water, water of constitution, adsorbed water, fiber saturation point are some of the terms that have been used to describe the water in pulps and papers. The origin of each term can be traced to either theoretical considerations or to the experimental method of measurement. Bound water has been the most popular term used to describe the associated water. Bulk water or free water is that portion of water not associated (or not bound) with the fibers. Two measurement techniques may not yield identical values of bound water. 

Also in Table V, some measured fiber saturation points are listed. The additional moisture at 100% RH in the modified materials is present in submicroscopic water pockets within the substance. It would now be expected that there would be a marked increase in the rate of diffusion of water-soluble materials through the swollen substance. This was described in a previous publication (37). 

The physical effect, which is measured quantitatively, is a marked increase in fiber saturation point, or moisture content of the substance at 100% relative humidity. With hardwoods treated with 1% NaOH, followed by washing, the swelling capacity of the cell walls is doubled. This increase in FSP not only provides for improved diffusion conditions of water-soluble materials, it also provides for improved enzyme-substrate interactions. In addition, there is an indication of a small increase in the maximum molecular weight of globular proteins capable of diffusing into the substance. 

Measurement of Density. Density of wood is expressed in a number of different ways, and a short explanation may be in order. The density of cell wall substance is generally assumed to be constant, so the density of a piece of wood obtained by measuring its overall weight and volume becomes a measure of wood porosity. Wood density is therefore related to many other wood properties. These relationships would become obscured if the moisture contained in wood were included in the measurements, especially in the case of wood above the fiber saturation point. 

The distinction between fiber saturation point (the maximum water content of swollen cell walls) and the maximum possible moisture content has a diminishing value for degraded wood, which may eventually have no effective fiber saturation point at all. The ordered and disordered cellulose in sound wood are the main sites for water adsorption (ii). As they diminish over time, their relative role in determining fiber saturation also diminishes. Nevertheless, the measurement of relative water adsorption will have some value in determining the relative degradation in a wood sample. 

Springer, E., Isak, H., and Weigand, H., Die kapazitat von aluminium oxid gegen uber salbengrand stoffen. Arch. Pharmaz. Ber. dtsch. Pharmaz. Ges., 291, 339, 1958. Eeist, W. C., and Tarkow, H., A new procedure for measuring fiber saturation point, J. Appl. Polymer Sci., 11, 149, 1963. 

Total amount of water in fibrous materials can be easily measured by use of gravimetric methods. There are also several methods that allow the measurement of the amount of total bound water, such as water retention value (WRV], fiber saturation point (FSC], and differential scanning calorimetry (DSC]. 

Raman and UV-Vis spectra were recorded on the bisected pellets at several points in time after impregnation. UV-Vis spectra were obtained using a house-built set-up, which is schematically depicted in Fig. 4. The use of optical fibers with different diameter allows one to record a UV-Vis spectrum from a small spot of 50- 100 pm on the sample. Manipulation of the sample can be carried out with great precision with the aid of an automated X-Y-Z-table. The sample is placed in an environmental cell under water-saturated air to prevent dehydration of the wet pellets during measurements. 

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