Humidity absorption

PUs sheets of different thickness, previously completely maturated, were anhy-drided at 60°C under vacuum of 0.1 mm Hg in the presence of anhydrous CaCl2 up to constant weights. On these films, the humidity absorption rate was measured by the increase of their weight under the same atmosphere conditions as those used in the maturation postcure process (e.g. 25°C and 50% RH). 

Low humidity absorption glass is an acellular material, so humidity cannot penetrate the filaments surface. 

Another, example can be found in fuel element fabrication facilities in which it is necessary to mix UOr or PuQi in batches as large as possible. From the criticality safety point of view, such operations are possible only if the materials are very low moderated. Experiments have been conducted to measure the maximum humidity absorption ratio of different salts (Fig. 1). Acceptable batches may then be established for a blender taking into account a humidify ratio including a safefy. marigin. ... 

In this cell structure model, the plant gum provides a protective barrier towards diffusion of oxygen into the polymerized urushiol inside, resulting in and explaining the high durability of Japanese lacquer films. Since the plant gum is hygroscopic, absorption of humidity would break down the barrier characteristics, and thereby causes degradation of the polymerized urushiol in the lacquer film, but a combination with hydrohobic polymerized urushiol results in a cell structure wall of low humidity absorption. 

As explained in Sect. 3.5, also humidity absorption can change the electromechanical properties of an actuator considerably. Therefore, measurement of both -ambient temperature and relative humidity level - is necessary for proper eleetro-mechanical characterization of the actuators. 

Water absorption of Tefzel is low (0.029% by weight), which contributes to its outstanding dimensional stabiUty as well as to the stabiUty of mechanical and electrical properties regardless of humidity. 

Precipita.tlon. An ink may also be caused to dry by precipitation of its binder rather than by evaporation of solvent. This can be accompHshed by a dding a diluent, such as water in the form of steam or humidity, to a hygroscopic solvent ink system, which causes the solubiHty of the resin in the ink film to decrease sharply and causes it to precipitate when its tolerance for the diluent is reached. Eurther drying is accompHshed by absorption of the solvents into the stock and then by evaporation. Another form of precipitation setting is the quick-set mechanism. This utilizes resins held in solution in a relatively poor solvent, by means of a small amount of an exceUent solvent (called a sweetener) blended with it. When the ink film is printed on the paper, an amount of the solvents is absorbed reducing the content of the sweetener solvent to a point which causes the resins to precipitate and the ink to set. 

A second type of uv curing chemistry is used, employing cationic curing as opposed to free-radical polymerization. This technology uses vinyl ethers and epoxy resins for the oligomers, reactive resins, and monomers. The initiators form Lewis acids upon absorption of the uv energy and the acid causes cationic polymerization. Although this chemistry has improved adhesion and flexibility and offers lower viscosity compared to the typical acrylate system, the cationic chemistry is very sensitive to humidity conditions and amine contamination. Both chemistries are used commercially. 

Interlayer moisture is one of the important controls for PVB-to-glass adhesion of current formulations (although moisture-insensitive formulations are being developed). The moisture content equiUbrates with the relative humidity to which the interlayer is exposed and thus is variable. Prior to lamination, interlayer moisture content is measured by one of three methods. The most rapid is by air absorption using a spectrophotometric technique to determine a... 

Anhydrous sodium tripolyphosphate is slow to hydrate in contact with the atmosphere under normal ambient conditions and generally remains free-flowing. If the relative humidity is below a critical relative humidity, which is different for both anhydrous forms of STP and dependent on temperature, hydration does not take place. For prolonged storage at room temperature, relative humidities above ca 60% in the air result in water absorption. For shorter periods, high levels of humidity can be tolerated. However, even at higher humidities, the amount of water absorbed is small. The heats evolved from vapor hydration of STP-I and -II have been estimated at 343 and 334 kj /mol (82.0 and 79.9 kcal/mol), respectively (25). 

The hygroscopic and humectant properties of com symps are of great importance in many apphcations. Depending on the type of symp and on the specific conditions of temperature and humidity, the products may either resist or facihtate moisture loss or moisture absorption. The abihty to attract moisture or retard its loss increases with increasing DE value. Prevention of moisture pickup is more characteristic of symps having low DE values. 

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