Sorption humidity experiments

In another work, Nordon and David [44] have modified their analysis to take account of the two-stage sorption behavior of a textile material and moistness dependence of the transfer rate. Use of this elaboration does not alter the essential conclusions of Henry s linearized analysis. A wad of textile material exposed to a sudden rise in ambient relative humidity experiences the passage of the fast temperature front with a rise in temperature, and a slow front with a drop in temperature of equal magnitude. Of the two corresponding humidity fronts, only the slow one is obvious as the fast one is very small and superimposed on the major one. 

The exposure of heterogeneous materials to humid environments induces different morphological changes of the polymeric structure, depending on the affinity and mode of sorption of the water. Moy and Karasz 16) presented sorption experiments of... 

Epoxy glasses aged at 140 °C were subjected to 40 °C/98 % relative humidity moisture penetration. Figure 31 shows the results of this transport experiment. We observed both a decrease of initial sorption kinetics as well as a decrease of equilibrium sorption level as a function of aging time. This supports the idea that during sub-Tg annealing, the resin contrasts and densities, resulting in decreased free volume. 

Although there is no bulk liquid with which adsorbed cations can be exchanged in the experiments made in atmospheres of controlled relative humidity, successive experiments can be made with different adsorbed cation populations, and it is found that the succession of dehydration steps varies with size and hydration energy of the cation (Posner and Quirk, 1964). There is also a dependence upon the type and extent of substitution in the aluminosilicate framework White (1958), for example, observed that two montmorillonites with the same cation-exchange capacity, loaded with the same cation, may have different water sorption and swelling properties. 

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. 

In the water absorption study, a Setaran thermobalance B 60 and a Richard Eyraud isotherm differential microcalorimeter were used. The same experiment permits one to obtain both the sorption isotherm and the differential heat absorption values ( ). The accuracies were better than O.I mg and 10 cal/sec, respectively. The relative humidity was obtained by changing the temperature of a water/ice bath (accuracy 0.1°C) which was connected to the sample. We measured both the amount of absorbed water and the heat of absorption after a change in the relative humidity level. We can therefore define the average heat of absorption per water molecule corresponding to the molecules which have been absorbed after this change in water relative humidity. 

The amount of moisture sorbed by the lyophilized protein sample is directly related to the activity of DjO vapor phase (i.e., RH) to which the protein is exposed. To maintain constant RH throughout the experiment, solid-state amide HX is usually carried out inside a sealed desiccator. The desired RH can be easily maintained by using a suitable saturated salt solution [62]. Some commonly used salts and the resulting %RH are LiCl (11% RH), KCjH30 (23% RH), MgCl (33% RH), I C03 (43% RH), and NaCl (75% RH) [60]. The RH values correspond to the RH over aqueous solutions of these salts at room temperature the humidity over D O is assumed to be identical. To control the rate of moisture sorption and prevent powder collapse in formulations containing hygroscopic excipients... 

The water vapor sorption experiments were generally performed in a Cahn D-200 electronic microbalance (with a sensitivity of lO g) enclosed in a thermostated reactor (Figure 5). The sample is placed in a pan and dried at 0% humidity. After reaching a plateau, the dry mass is achieved. Thereafter, the sample is exposed to vapor pressure and the mass gain is measured as a function of time until reaching the equihbrium state. The mass equilibrium is obtained at each humidity level tested. 

The main choices one has to decide on in performing a TGA experiment are the sample pans, the sample size, the temperature program, including possible isothermal steps and the gas environment—either inert or oxidative. Occasionally, it may be helpful to add moisture to the TGA s gas stream to measure moisture sorption/desorption properties (see Section 3.4.4 and Fig. 3.15) or to test a polymer s susceptibility to hydrolysis. Several manufacturers sell accessories that allow the operator to control the room temperature humidity of the purge gas (see Section 3.7 on instrumentation). A fritted glass bubbler can also be employed to saturate the purge gas with water. 

In the experiments conducted with additives the amount of additive was kept around 10 % of the solid material. From the point of view of solid waste disposal and possible utilization of this product, the CaS03/CaS04 ratio plays an important role. In general, CaS03 is not desired in the product. The contact time in the spray drier was less than one second. On the other hand, residence time in a conventional spray drier is between 5 and 12 seconds. Results of this work showed that over 70% SO2 removal could be achieved in such a short contact time. This indicates that most of the sorption reaction takes place in a small region around the nozzle. Reaction between SO2 and droplets takes place with a simultaneous evaporation. After the drying is completed the reaction probably continues, but at a relatively slower rate in the presence of moisture. If the relative humidity is not sufficiently high, no ftirther sorption of SO2 can be expected after completion of the evaporation step. 

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