Water sorption testing

Figure 4.19 Water sorption test on two calcium oxide samples. Samples were exposed at 100-200 Pa water partial pressure at 23 °C. Sample A was prepared by SAES according to a proprietary process to increase material surface area and porosity.

The complex sorption behavior of the water in amine-epoxy thermosets is discussed and related to depression of the mechanical properties. The hypothesized sorption modes and the corresponding mechanisms of plasticization are discussed on the basis of experimental vapor and liquid sorption tests, differential scanning calorimetry (DSC), thermomechanical analysis (TMA) and dynamic mechanical analysis. In particular, two different types of epoxy materials have been chosen low-performance systems of diglycidyl ether of bisphenol-A (DGEBA) cured with linear amines, and high-performance formulations based on aromatic amine-cured tetraglycidyldiamino diphenylmethane (TGDDM) which are commonly used as matrices for carbon fiber composites. 

Kinetic studies in sediment/water systems with Direct Red 2, Acid Black 92, Acid Red 4, Acid Red 18, and Direct Yellow 1 lead to linear and biphasic plots of dye loss over time. For all but Direct Yellow I, dye loss was usually preceded by a lag or adaptation phase. Acid Black 92 and Direct Red 2 were transformed completely in less than 24 and 48 hours, respectively, but Acid Yellow 151 and Direct Yellow 1 showed half-lives of greater than 2 years. The rapid initial drop in concentration of all dyes observed, with the exception of Acid Red 18, was presumed to be due to sorption. Tests to determine the effect of pH on... 

Tagami, H., Kanamaru, Y., Inoue, K. et al. Water sorption-desorption test of the skin in vivo for functional assessment of the stratum corneum. J. Invest. Dermatol. 78, 425-428 (1982). 

In situ (field) batch sorption tests use measurements of the radionuclide contents of samples of rock cores and consanguineous pore water obtained at a field site. The advantage of this approach is that the water and rock are likely to be... 

The effects of drought, i.e., the quantitative properties of water in fresh and dry leaves of durum wheat were tested by the relation between the water status and the properties of bound water (BW) with different strengths to ionic, polar, or hydrophobic sites of macromolecules [56]. An increase in tissue affinity for strongly bound water implied a simultaneous increase in the affinity for weakly bound water. The qualitative properties of bound water may be particularly important for drought adaptation in durum wheat, which is associated with solute potential plots of differential energies of water sorption (Figure 4). 

The water-sorption experiments were carried out in a dynamic flow vapor sorption apparatus (Model SGA100, VTI Corporation, Hialeah, FL). Samples of the two polymorphs were placed in the instrument s sample chamber and their moisture uptake as a function of relative humidity (RH) was measured. Water-sorption isotherms for both polymorphs were carried out imder the temperature conditions of 20, 25, 35, and 45°C. The amoimt of sample used for an analysis depends on the sample s tendency to pick up water. If the sample is highly hygroscopic, about 2-5 mg is sufficient for the test, but if the sample is nonhygroscopic, a larger mass is needed, about 25 mg or more. For this study, water-sorption isotherms for both polymorphs were carried out using the flow system and a sample size of about 50 mg. 

Swelling or sorption test of liquids and vapours through the rubber is obtained by the standard method of ASTM D 814 and ISO 6179 2010 as a general method for various types of rubber. Other standard methods to test liquid and water vapour transmission rate are displayed in Table 27.1. Gas permeation test is obtained by the standard method of ASTM D 1434-82 and ISO 2782 as a general method, especially for oxygen gas mostly using ASTM D 3985 as a protocol for measurement. Table 27.2 exhibits the standard methods of gas permeability test. 

The results were compared with the oxygen diffusion, solubility, and permeability coefficients obtained for PET films under the same conditions. The water sorption isotherm for polylactide films was also determined. Diffusion coefficients were determined with the half-sorption time method. Also, a consistency test for continuous-flow permeability experimental data was run to obtain the diffusion coefficient with the lowest experimental error and to confirm that oxygen underwent Eickian diffusion in the polylactide films. The permeability coefficients were obtained from steady-state permeability experiments. The results indicated that the polylactide films absorbed very low amounts of water, and no significant variation of the absorbed water with the... 

Water sorption isotherm is itseful for predicting water sorption properties of polymer and allowed to provide little insight into the interaction between water molecules and polymer tested. 

Figure 20.8 Subtraction of FTIR spectra collected at different sorption times in the case of water vapor sorption test 70/30 PP/PE/EVOH 61m. Reprinted with permission from Ref [79] 2009, Elsevier.

As part of the salt screening process, the potential formation of polymorphic forms and solvates should be evaluated to determine which salt form is most appropriate for development based on target attributes (see also Chapter 2). Each potential salt and/or polymorphic form should be evaluated to ascertain its stability at accelerated conditions (temperature and humidity). The water sorption of each should be evaluated to determine if the material will likely be incompatible with excipients that contain moisture. Following the synthesis of different salt forms each must be evaluated by a battery of chemical and physical tests. Given the importance of this work, an entire chapter in this text is devoted to solid-state characterization and the reader is encouraged to peruse them for further details. 

The obtaining of good mechanical properties is obviously an important issue because the end of a fuel cell test is directly related to a general or local membrane breaking. To our knowledge, the study of SPI mechanical properties is limited in the literature to the measurement of stress-strain curves in the dry and water-swollen states [39,110,112,126]. These curves present an elastic behavior limited to few percent of deformation followed by a plastic linear behavior (Fig. 44). Despite the polymer being in a glassy state, the water sorption induces plasticization. The maximum tensile stress at break is of the order of 70 MPa for SPI compared to less than 20 MPa for Nafion and the elon-... 

The swelling in liquid water could be a nonrelevant value to describe the membrane behavior in fuel cells. As an example, the sulfonated polyether ketones suffer from an excessive water uptake when immersed in hquid water at elevated temperatures [110], while a high-temperature fuel eeU test over 1400 h has been performed with fully hydrated gases [2]. Therefore, the swelling in hquid water at elevated temperature is of limited value. Most of the authors prefer nowadays to determine the water uptake under defined temperature and RH conditions. Water sorption isotherms have been measured and analyzed [40,104,119]. These results confirmed the previous data since the sorption isotherms are superimposable when expressed in 2 values for different ion contents and chemical structures [40,48,49,56]. The sorption isotherms were classically analyzed as the superposition of different phenomena (Henry, clustering, dual-mode, Flory-Huggins, and BET II processes) [119]. The water sorption isotherms exhibit a distinct sorption-desorption hysteresis, which was attributed to the very low desorption process [40]. 

Yamada et al., 2005 Yin et al., 2005). Proper selection of the nonsulfonated diamine monomer allowed for control of important membrane properties, including water sorption and mechanical strength. For example, it was shown that the incorporation of bulky or angled co-monomers (aromatic diamines) improved the water retention capability of SPIs, leading to very high proton conductivities (Zhang and Litt, 1999), but the mechanical properties (brittleness) and hydrolytic stability of these polymer were unattractive. They have not yet been fabricated in MEAs and tested in a fuel cell. 

Water sorption studies were conducted on the cast sheet according to ADA Specification No. 12. The disk thickness was a nominal 0.75 millimeter instead of the required 0.5 millimeter. The test period was extended until the samples reached apparent equilibrium. For most samples the apparent equilibrium was reached at 250-275 days. 

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