Sorption moisture

Fig. 3. Effects of composition on physical properties. A, acetyl B, butyryl C, cellulose. 1, increased tensile strength, stiffness 2, decreased moisture sorption 3, increased melting point 4, increased plasticizer compatibiUty 5, increased solubiUties in polar solvents 6, increased solubiUties in nonpolar...

Satriana. Moisture Sorption of Lead Beta Re-sorcylate Salts , PATM 2022 (1971) 51) M. 

Fig. 5. First (open circles) and second (full circles) equilibrium moisture sorptions in the DGEBA-TETA neat resin. The dotted line is eq. (1)...

Table I. Moisture Sorption/Dlffusion Parameters for Polyester/Glass Fiber Laminates...

The Clausius-Clapeyron equation implies that if we plot the natural log of the pressure of the gas phase versus inverse temperature, the slope of the resulting line is the heat of vaporization divided by the gas constant (R). A plot of In P (vapor pressure of water) versus inverse temperature is given in Figure 3. The calculated heat of vaporization (determined by multiplying the slope by R) is 10,400 cal/mol. The important aspect of Eq. (10) with regard to moisture sorption is the fact that increasing the temperature also increases the vapor pressure. 

IV. HEAT TRANSPORT CONTROLLED MOISTURE SORPTION (PURE WATER ATMOSPHERE)... 

A model describing moisture sorption for a deliquescent solid in a pure water vapor atmosphere is developed in this section. Under such conditions there is no... 

In Section IV it was assumed that all resistance to moisture sorption was due to heat transport. This assumption is valid only in cases where there are no other... 

The basic assumption for a mass transport limited model is that diffusion of water vapor thorugh air provides the major resistance to moisture sorption on hygroscopic materials. The boundary conditions for the mass transport limited sorption model are that at the surface of the condensed film the partial pressure of water is given by the vapor pressure above a saturated solution of the salt (Ps) and at the edge of the diffusion boundary layer the vapor pressure is experimentally fixed to be Pc. The problem involves setting up a mass balance and solving the differential equation according to the boundary conditions (see Fig. 10). 

As one might expect, moisture sorption is controlled by both mass and heat transport resistance. The heat transport model discussed earlier was based on the concept that condensation of water would generate heat, which at steady state would... 

The result shown in Eq. (54) is a square root of time relationship for moisture uptake. Mulski [20] demonstrated that for sodium glycinate in a hydrophobic porous matrix, moisture sorption follows Eq. (54). 

Surface area and moisture uptake have been related to the disintegration properties of excipients such as crosspovidone, starch, and alginic acid [17]. The surface areas of the three materials were measured, and a linear correlation was found between the maximum moisture sorption and specific surface area for the three disintegrants. The greater the surface area of the material, the more numerous were the sites for capillary attraction of water to its surface. It was postulated that the capillary action appears to be responsible for the disintegration properties of the materials. 

Figure 4 also shows the excellent fit to the GAB equation (Eq. 10) of the sorption and desorption isotherms for microcrystalline cellulose. In this regard, this equation offers considerable practical utility in fitting isotherms for these types of materials over the entire relative humidity range, especially in contrast to the BET equation, which usually only fits uptake data up to about 40% relative humidity. As we have mentioned, however, this does not in itself confirm the validity of the GAB model for describing moisture sorption data on these materials. Rather, independent confirmation of the physical meaning is necessary. 

Bell, L.N. and Labuza, T. P. 2000. Moisture Sorption Practical Aspects of Isotherm Measurement and Use . 2nd Ed. American Association of Cereal Chemists, St. Paul, MN. 

Kapsalis, J.G. 1987. Influence of hysteresis and temperature on moisture sorption isotherms. In Water Activity Theory and Application to Foods (L.B. Rockland and L.R. Beuchat, eds), pp. 173-213. Dekker, New York. 

In any study of the moisture sorption-desorption properties of modified wood, the moisture content of the samples is determined using gravimetric methods. Invariably, the EMC of the sample is based upon the oven-dry weight of the modified wood ... 

Popper and Bariska (1972) studied the moisture sorption properties of wood chemically modified with acetic (or phthalic) anhydride and analysed the results using Brunauer-Emmett-Teller (BET) theory and the H-H model. Acetylation was found to reduce the number of sorption sites, whereas little effect was noted with phthaloylation. By dividing the sorption isotherm into a monolayer component and a multilayer component using the H-H model, it was shown that there was a large reduction in the... 

A recent study of wood modified with a variety of anhydride reagents has questioned the validity of the use of the H-H model when interpreting the moisture sorption isotherms of modified wood (Papadopoulos and Hill, 2003). This has shown that although modification with anhydride reagents leads to a reduction in both monolayer and... 

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