Water uptake immersion measurements

It is well known that swelling of resins increases the particle radius. When resin beads are immersed in the solution, water uptake takes place almost immediately, resulting in a new swollen radius. The swollen radius is inversely proportional to the initial solution concentration (Hellferich, 1962). This effect has not been taken into account in the original model of Levenspiel (1972). However, the actual swollen radius of the resin should be used in the model equations, and so measurements should be performed in order to estimate this radius. 

The dependence of the concentration of ionized groups (and consequently the water uptake) on the duration tgx of th immersion in the solution leads to an additional dynamical hysteresis in the sensor output characteristic which can be minimized by setting constant tgx for all pH measurements. 

The method used to evaluate the porosity qualitatively is very simple. After weighing, aggregates of a known size are put into a vacuum chamber for 1 hour. Then they are immersed in water for 24 hours. After that, the weight is measured again. The water uptake in wt% of the original weight is taken as a measure of the porosity. 

Measurement of the water content of crosslinked gels. Crosslinked gel films were immersed in PBS solution of pH 7.4 at 37°C for 20 hr. After the weight of wet gels was measured, they were placed in a vacuum oven for 6 hr at 60°C and 0.1 torrs and the weight of dried gels was measured. The water content (water uptake + water moisture) of the crosslii ed gels was calculated from the following equation ... 

Regarding the water uptake of starch, several tests are currently being performed in order to evaluate the influence of blending TPS with NR. These tests comprise, firstly, the measurement of water uptake by the total immersion of the materials produced in water. The samples are weighed before and after the immersion in order to measure the water uptake. Secondly, the measurement of the equilibrium contact angle of a drop of water placed over the surface of the materials. Taking the hydrophobic nature of NR into consideration and the high compatibility reached between both polymers in this research, a decrease in water uptake is expected. 

From the measurement of the water uptake in the first hours of immersion, some qualitative information on this delamination can be obtained. From the coating capacitance (Cpf) against time plot of Figure 19 it is clear that the coating does not show stable Fickian water uptake but shows deviations that are probably... 

Water uptake is defined as the water that is absorbed into the gel when a highly absorbent polymer has been swollen in solution (ion exchanged water or salt solution) and has reached equilibrium. General measurement methods involve immersion of the sample in a solution for a certain specified time to measure the weight or voliune of the swollen gel (see Table 1) [154]. For example, there are methods to measure weight increase of a nonwoven cloth bag in which superabsorbent polymer is placed (e.g., like a tea bag) or to measure the volume of the solution by putting the polymer in contact with the solution. 

Four common superabsorbent polymers were examined for their water uptake at seven organizations under many different conditions. These included using two types of testing solution, two materials for tea bags, immersion time, temperature, measurement temperature, type of solution, conditioning of the sample, the amount of the sample, type, and particle size. The obtained results have been analyzed and the reproducibility from each organization and each measurement have been evaluated. 

All adhesives absorb water, and water uptake data for a number of structural adhesives are collected in Table 31.3. Such data are obtained by measuring the weight of water absorbed by an immersed film, and include the diffusion coefficient D and the weight absorbed at equilibrium M. This means that adhesive layers in joints will absorb water and its vapor, and transmit it to the interface. This cannot be prevented by sealing the edges with a paint or lacquer, as these also absorb water. The data can be used to calculate the rate at which water will enter joints, and water concentration profiles within them (Comyn 1983). This is discussed in more detail in Sect. 31.5.2. 

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]. 

A dermal absorption rate of 329 mnol/minute/cm ( 60 nmol/minute/cm ) was calculated for the shaved abdominal skin of mice (Tsumta 1975). This is equivalent to a human absorption rate of 29.7 mg/minute, assuming that a pair of hands are immersed in liquid chloroform (Tsumta 1975). However, this calculation was based on the assumptions that the rate of chloroform penetration is uniform for all kinds of skin and that the total surface area of a pair of human hands is 800 cm the former assumption is especially dubious. Islam et al. (1995) investigated the fate of topically applied chloroform in male hairless rats. For exposures under 4 minutes, chloroform-laden water was applied to shaved back skin for exposures of 4-30 minutes, rats were submerged in baths containing chloroform-laden water. Selected skin areas were tape-stripped a various number of times after various delay periods. It appeared that there was an incremental build-up of chloroform in the skin over the first four minutes. When compared to uptake measured by bath concentration differences, approximately 88% of lost chloroform was not accounted for in the stratum comeum and was assumed to be systemically absorbed. 

Of particular interest in the present study is the apparent existence of an activated sorption mechanism for nitrogen in partially hydrated zeolite NaA, a further study of which is planned. The less definitely established irreversibly sorbed nitrogen on dehydrated zeolites NaA and NaX, but not on CaA and NaY, is in need of confirmation, and of further characterization. A practical utility of the results is the quantifying of nitrogen uptake from air, which persists even with appreciable sorbed water. This amount can be approximated from the isotherms as the capacity at 0.8 atm. inasmuch as the contribution due to oxygen is very small. Conversely, the isotherms can be used to assess the state of hydration of a zeolite, with the aid of a measurement of the amount of sorbed nitrogen, either by mass loss on evacuation at room temperature in a balance, or by collection of gas evolved on immersion of a sample in water. 

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