Sorption of Water Vapor

Water vapor is the main sorbate used for the study of the sorption properties and structure of various cellulose materials such as cellulose powders, films, and fibers of regenerated cellulose, textile materials, pulp, paper, cardboard, and some other materials. Sorption of vapors is usually described through isotherms having various shapes that express the relative amount of sorbate in the sorbent A, g/g) as a function of relative vapor pressure ( p = p/Po) at a constant temperature (Gregg et al., 1982]. To calculate sorption parameters and structural characteristics of sorbents, the obtained isotherms should be linearized by the appropriate equations corresponding to the assumed sorption mechanism. 

Isotherms of type 1 exhibit a saturation plateau due to adsorption of an inert sorbate on the surface of pores. In this case. 

The sorption experiments were carried out at 25°C on a vacuum Mac-Ben apparatus having helical spring quartz scales. Prior to starting of the experiments the samples were dried at 105°C up to constant weight and additionally degassed in the sorption device. 

Sorption of water into non-crystalline domains of cellulose (NCD) at various -ranges was calculated using the additive functions of Van Krevelen (Van Krevelen, 1972). 

The investigations showed that sorption isotherms of water vapor by various cellulose samples are sigmoidal. Moreover, with an increase in the amorphicity degree Y from 0.25 to 1, sorption capacity of the samples is enhanced (Fig. 7.29). 

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The sorption of water vapor onto nonhydrating crystalline solids below RHq will depend on the polarity of the surface(s) and will be proportional to surface area. For example, water exhibits little tendency to sorb to nonpolar solids like carbon or polytetrafluorethylene (Teflon) [21], but it sorbs to a greater extent to more polar materials such as alkali halides [34-37] and organic salts like sodium salicylate [37]. Since water is only sorbed to the external surface of these substances, relatively small amounts (i.e., typically less than 1 mg/g) of water are sorbed compared with hydrates and amorphous materials that absorb water into their internal structures. 

It is not correct, however, to regard activated carbon as hydrophobic. The equilibrium sorption of water vapor on an anthracite-derived activated carbon is compared with that of other sorbents in Fig. 2. The sorption of water vapor on activated carbon follows a Type V isotherm (according to... 

Fig. 2. Equilibrium sorption of water vapor from atmospheric air at 25° C on (A) alumina (granular) (B) alumina (spherical) (C) silica gel (D) 5A Zeolite and (E) activated carbon. The vapor pressure at 100% R.H. is 23.6 Torr (Yang, 1997).

Figure 1-12 Sorption Isotherms of Wheat Flour, Starch, and Gluten. Source From W. Bushuk and C. A. Winkler, Sorption of Water Vapor on Wheat Flour, Starch and Gluten, Cereal Chem., Vol. 34, pp. 73-86, 1957.

Bushuk, W and C.A. Winkler. 1957. Sorption of water vapor on wheat flour, starch and gluten. Cereal Chem. 34 73-86. 

Fig. 2. Isothenns of the sorption of water vapor by the following preparations / hydrate cellulose 2 mixed polysaccharide (III) containing 10 mol.-% of altro-pyranose units 3 mixed polysacdkride (III) containing 31 mol.-% of altropyranose units 4 cotton cellulose 5 mixed polysaccharide IV containing 3,6-anhydro-...

Heats of Sorption as Functions of Amount Sorbed. The integral (Ai ) and differential (AH) heats of sorption of water vapor were obtained from the relationships... 

The sorption of water vapor onto non-hydrating crystalline solids below RHq will depend on the polarity of the surface(s) and will be proportional to surface area. For example, water exhibits little tendency to sorb to non-polar solids like carbon or polytetrafluoroethylene... 

Sorption of water vapor by polymers is a diffusions process (9). The rate and extent of water sorption depends on the diffusion coefficient of water in the polymer, on the water/polymer interaction, and on the temperature. 

Saravacos, G.D. and Stinchfield, R.M. Effect of temperature and pressure on the sorption of water vapor by freeze-dried food materials, /. Food Sci., 30,779,1965. 

To study the structural features of preparations erf mixed polysaccharides, we investigated the process of sorption of water vapor on a vacuum sorption setup of the McBain type (Fig. 2). The elata show that preparations of mixed polysaccharides sorb a larger amount of moisture than cellulose, even in the case of mixed polysaccharide (IV) where the number of hydroxyl groups decreases as a result of the forma-... 

Sokolowska, Z. 1989. On the role of energetic and geometric heterogeneity in sorption of water vapor by soils Application of a fractal approach. Geoderma 45 251 -265. 

Type of data sorption of water vapor into block copolymer films... 

Maximum sorption of water vapor from saturated atmosphere (RH = 100%). 

Figure 12.7 shows a set of isotherms for sorption of water vapor on the most frequently used sorbents. A variety of sorption isotherms, which frequently change the slope at certain moisture concentrations, complicate direct comparison of different sorbents. Specifically, an average sorption capacity over the entire range of moisture concentrations might not be representative of that over the narrow range of moisture concentrations to be used in a partic-... 

Figure 8.83 shows the schematic construction of a chemomechanical rotor, where anisotropic expansion causes rapid bending of the film due to the sorption of water vapor from one side of the film [140]. The rotation continued until the adsorbates were completely vaporized. This moving device may become a clean and silent power source for use as a molecular engine where the chemical free adsorption energy is transduced into the mechanical work. 

Okuzaki, H., and K. Funasaka. 2000. Electro-responsive polypyrrole film based on reversible sorption of water vapor. Synth Met 108 127. 

Sakurai, K., Minami, A., and Takahashi, T. 1984. Sorption of water vapor by chitosan membranes. Sen-i Gakkaishi 40 T425-T430. 

It is not correct, however, to regard activated carbon as hydrophobic. The equilibrium sorption of water vapor on an anthracite-derived activated carbon... 

At diffusion MS from films, also as well as in case of sorption by films ChT-AM of water vapor, have anomalously low values of the parameter n, estimated in this case from the slope in the coordinates lg(G/G )-lgt. Increase the concentration of MS and time of isothermal annealing, as well as in the process of sorption of water vapor films, accompanied by an additional decrease in the parameter n. sym-biotically index n also changes magnitude a. Moreover, the relationship between the parameters of water sorption films ChT-AM (values of diffusion coefficient, an indicator n and values of equilibrium sorption Q) and the corresponding parameters of the diffusion of MS from the polymer film on condition G/G < 0.5 is shown. 

Okuzaki H, Kuwabara T, Kunugi T (1997) A polypyrrole motor driven by sorption of water vapor. 

The blended PP/polyamideurea fibers have better sorption and eleetrie properties (higher sorption of water vapor and dyestuffs, lower electrostatic charge) and changed tensile properties, e.g., lower tenacity [115]. 

Wlochowicz, A. Wojciechowska-Bujok, E. Effect of dyeing on sorption of water vapor by wool. Text. Res. J. 1987, 57, 503-508. 

Miyagi, K.T.Z. Sorption of water vapor by poly(vinyl acetate). Colloid Polym. ScL 257, 259... 

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