Water Uptake Testing Method

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. 

There is a method to measure the change in UV absorption of a solution by immersing the superabsorbent polymer in a solution in which a UV absorber that cannot be absorbed by the gel is added. Upon UV measurement, swelling equilibrium is calculated. The advantage of this 

Tea bag method The superabsorbent polymer is placed in a nonwoven cloth bag, then it is immersed in aqueous solution, and finally weighed after removing the nonabsorbed water 

Centrifugal dehydration method After the superabsorbent polymer is sufficiently swollen in an excess-aqueous solution, the swollen polymer is placed in a screen bag and water is expelled by centrifugal force. The recovered water is measured. 

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For standardization of the water uptake test, multiple organizations conducted the round robin test using common samples and procedures. Based on their results, methods (proposal) to determine water uptake and the rate of water absorption are being developed. A written inquiry was also distributed to the member companies of the Polymer Materials Center regarding water upUdce. Currently, Ihe standard for water uptake has not been established anywhere in the world. It seems important first to establish the standardization of Ihe water uptake testing method for superabsorbent polymers and then to make it die international standard. The testing mediods (proposal) shown here are still under discussion and when it is standardized by JIS, there may be partial modification. 

Water molecules movement, polymer gels, 375-6 Water uptake testing method, superahsorhent polymers, 292-356, 357... 

Electrochemical tests This group includes the various electrochemical tests that have been proposed and used over the last fifty or so years. These tests include a number of techniques ranging from the measurement of potential-time curves, electrical resistance and capacitance to the more complex a.c. impedance methods. The various methods have been reviewed by Walter . As the complexity of the technique increases, i.e. in the above order, the data that are produced will provide more types of information for the metal-paint system. Thus, the impedance techniques can provide information on the water uptake, barrier action, damaged area and delamination of the coating as well as the corrosion rate and corroded area of the metal. However, it must be emphasised that the more comprehensive the technique the greater the difficulties that will arise in interpretation and in reproducibility. In fact, there is a school of thought that holds that d.c. methods are as reliable as a.c. methods. 

Fat absorption and binding properties are determined by mixing food ingredients with fats and oils, and after a separation step (centrifugation) the amount of oil absorbed is measured. The test is similar to water uptake, that is, the method includes steps of subdivision, agitation, separation, and measurement. 

Water Absorption. The water absorption was tested according to ISO 62-1980, method 1 (immersion in water of 23°C for 24 1 hours), using a test specimen, of 50 mm in diameter and a thickness of 3 mm. The water uptake was 0,05 %. Comparable novolak hardened systems have slightly smaller water absorptions in the range of 0,03 to 0,04 %. 

Various tests and analytical methods are used for the characterisation and evaluation of the properties of vegetable oil-based polymer composites. Mechanical tests for properties such as tensile, flexural, compressive, impact, hardness and wear are carried out by a universal testing machine (UTM), and by equipment for testing impact, hardness, abrasion loss, and so on. Weather and chemical resistance tests are performed in UV/ozone, an artificial environmental chamber and in different chemical media. Water uptake and biodegradability tests are carried out by standard ASTM methods. Biodegradability and biocompatibility may be studied by the same procedure as described in Chapter 2. However, in practice only a few such studies have been performed for vegetable oil-based composites. 

In order to standardize the method, the test has been adapted by using small (1.6 cm ) collagen sheets [7] which are incubated for 24 h at 50 C with the surfactant solution, in the presence of tritiated water of known activity. At the end of the incubation period, the radioactivity entrapped into the collagen piece is counted and converted into volume of water uptake per gram of dry collagen. 

In a laboratory test system, the reactant gas is usually humidified by passing it through a water bath in a bubble humidifier that is controlled at a desired temperature. This process assumes that the dew point of the air is the same as the temperature of the bubble humidifier. This temperature can be controlled independently of the cell temperature to achieve the desired gas RH. Water vapor is absorbed by the gas, and water uptake is a function of the water-gas interfacial area. This is a conventional humidification method and is widely used in small-scale laboratory fuel cells due to its simphcity and low cost, but it is not very practical to be used in large-scale stacks. The main disadvantages of the method are its hmited water transfer capacity and slow response to the changes in the RH level. 

Usually, PEMFC performance depends on the presence of a humid environment as well as the temperature of operation. Therefore, it is important to determine the water uptake and the stability of the prepared membranes in water at various temperatures. The temperature dependence of water uptake of the SPTES membranes was determined by the following procedure. The SPTES membranes were vacuum-dried at 100°C for 24 h, weighed and immersed in deionized water at various temperatures for 1 h. Subsequently, the wet membranes were wiped dry and quickly weighed again. The water uptake of SPTES membranes is calculated according to the method described in the Experimental section to obtain weight percent of water. The results are shown in Fig. 6.10 for comparison, the Nafion-117 membrane was also tested under the same conditions. 

Based on an inquiry made on behalf of the superabsorbent polymer manufacturers, performance testing items include appearance, smell, water uptake, water retention, rate of water absorption, particle size distribution, bulk density, pH, gel strength, durability, dry weights, residual monomer, and water soluble components. The testing items that should be standardized are water uptake and rate of water absorption [151]. Testing method preferences include ... 

Testing Method for Water Uptake of Superabsorbent Polymers (proposal, only the main text is extracted)... 

This standard specifies the test method of water uptake of superabsorbent polymers using the tea bag method. 

Remark 1. This test method specifies the test method for the superabsorbent polymers with water uptake 10 times the dry weight. 

Quantitative estimation of ventilation by indirect methods in mussels requires four assumptions (16) a) reduction of concentration results from uptake, b) constant ventilation (pumping) rate, c) uptake of a constant percentage of concentration (first order process), d) homogeneity of the test solution at all times. Our transport studies have utilized antipy-rine (22, 23) a water soluble, stable chemical of low acute toxicity to mussels. It is readily dissolved in ocean water or Instant Ocean and is neither adsorbed nor volatilized from the 300 ml test system. Mussels pump throughout the 4 hour test period and this action is apparently sufficient to insure homogeneity of the solution. Inspection of early uptake and elimination curves (antipyrine concentration as a function of time) prompted use of Coughlan s equation (16) for water transport. 

Quantitative measurement of diffusional uptake and carrier-mediated transport of nutrients and drugs in experimental animals was greatly facilitated with the introduction of Olden dorfs brain uptake index (BUI) [42].Test and reference tracers are injected as an intraarterial bolus into the carotid artery of the anaesthetized animal. After 5 s the animal is killed and the brain is removed for radioactivity counting. This method measures the ratio of the unidirectional brain extraction, E, of the test substance and of the reference ([ H]-water, [ " C]-butanol), which are labelled with different isotopes, during a single passage through the brain capillary bed ... 

If, during the bioconcentration test, the chemical concentrations in the organism and water reach steady-state, the bioconcentration factor can be calculated from the steady-state concentrations in the organism (CB) and the water (Cw) as CB/ Cw. However, when steady-state is not achieved during the test because the test was conducted for an insufficiently long period of time or because exposure concentrations were variable during the test, the derivation of the BCF and the rate constant for chemical uptake and elimination require a more specific method of data analysis. 

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