Swelling method, water absorption

Swelling method. Measurement of swelling is a second method used to estimate water absorption of a sample. A swelling apparatus was devised and described by Hermansson (, 13). In this method, a small amount of sample is dusted on a wet filter paper fastened on a glass filter. The filter is fitted on top of a thermostated funnel filled with water and connected to a horizontally located capillary. The uptake of fluid is followed in the capillary evaporative losses are prevented by a glass lid... 

The ASTM procedure covers an extended set of tests of wood-based materials, among them (Sections 100-111) tests for water absorption and thickness swelling, and for moisture content. The procedure describes two water absorption methods Method A, for 2 plus 22 h submersion period, and Method B, for single continuous... 

A number of sorbents have been proposed to clean water surfaces from oil [318]. The use of hydrophobic aerosil was proposed for this purpose, which, however, can hardly be accomplished for economic reasons. More promising seems to be the proposal to use natural materials for oil absorption, such as turf, diatomite, vermiculite, swelled perlite. A method has been proposed for the modification of perlite by a consequent treatment with cationic surfactants and higher carboxylic acid salts. Such modification of swelled perlite increases its oil capacity up to 600%, the water absorption decreases 10 -100-fold, and the sinkability decreases considerably. The degree of oil removal from the water surface is, according to in vitro tests data, 98 - 99%. Methods have been found to use oil-saturated sorbents. 

Measures to improve the moisture resistance of LPCs consist primarily of retarding the water absorption of cellulose fibers because it is virtually impossible to completely prevent their moisture absorption. A number of methods have been shown to retard moisture absorption in cellulose fibers, but they fall under two main categories water repellant treatments and dimensional stability treatments [17], as shown in Table 15.7. Whereas the water repellant treatment slows down the rate of water absorption, the dimensional stability treatment reduces the swelling in the fibers. 

The methods for the evaluation of intrinsic swelling, i.e. individual particle volume increase, are mostly based on the microscopic observation of particles. This presents the obvious advantage of allowing the direct measurement of the increase in disintegrant particle dimensions due to water absorption lO-H. 

The penetration of water into rubber is very slow compared with most organic liquids and, hence, with the usual test piece for the standard volumetric method, a very long time is required to reach equilibrium. For this reason, a procedure used to be included in BS 903 Part A16 (now BS ISO 1817) for expressing results of total immersion tests as a fraction of the surface area exposed for measurements when equilibrium swelling was not reached, on the basis that absorption is restricted to the surface layers. If the test piece is always standardised to the same dimensions it is not important which method of expression of results is used. 

The absorbency of wound dressings is determined by using BS EN 13726-1 2002, 3.2 free swell absorptive capacities. This is also known as BP method. For this test, 5 X 5 cm dressing specimens were prepared. The test solution A (2.298 g sodium chloride and 0.368 g calcium chloride dihydrate is added to 1 L of distilled water) is prepared for the experimental studies. The solution A is warmed to 37 1°C, and then 40 times the mass equivalent of the specimen is dispensed slowly and gently onto the specimens in the Petri dishes. The Petri dishes are then placed in an incubator for 30 min at 37 1°C (body temperature). After 30 min of conditioning, the dishes are removed from the incubator, suspended by one corner by using tweezers to allow excessive solution to drip off for 30 s, and reweighed for wet mass. 

The absorption rate behavior of crosslinked,water swellable polymers is explained in terms of diffusion of water into the polymer network. The absorption kinetics can be studied over time using a viscosity versus time measurement. Alternately, a one point determination of sorption time can be used to compare various polymers. The limitation of this method is that the polymers tested must have a sufficiently high swelling capacity so that the simplifying equations hold. This limitation can be eliminated by a proper choice of polymer/sallne solution ratio in the vortex test. The variables which control the absorption rate of ail the samples studied are swelling capacity, mesh size of powder particles and the distribution of particle sizes, the specific surface area of the product, and the apparent density of the polymer. 

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