Moisture water absorption

Aloisture Absorbent Synthetic Paper. Processes for making a water absorbent synthetic paper with dimensional stabihty have been developed by several companies. In a process developed by Mitsubishi Rayon, acrylic fiber is insolubilized by hydra2ine and then hydroly2ed with sodium hydroxide. The paper, formed from 100 parts fiber and 200 parts pulp, has a water absorption 28 times its own weight (96). Processes for making hygroscopic fibers have also been reported in the patent Hterature. These fibers are used in moisture absorbing nonwovens for sanitary napkins, filters, and diapers. 

Polyimide. Polyimide is a biaxiaHy oriented high performance film that is tough, flexible, and temperature- and combustion-resistant. Its room temperature properties compare to poly(ethylene terephthalate), but it retains these good characteristics at temperatures above 400°C. Its electrical resistance is good and it is dimensionally stable. The principal detriment is fairly high moisture absorbance. The main uses are for electrical insulation, particularly where high temperatures are prevalent or ionizing radiation is a problem. The films may be coated to reduce water absorption and enhance... 

Conformal coatings are protective coatings appHed to circuit board assembHes. They protect the interconnect conductors, solder joints, components, and the board itself they reduce permeabiHty to moisture, hostile chemical vapors, and solvents in the coating. Use of conformal coatings eliminates dendritic growth between conductors, conductor bridging from moisture condensation, and reduction in insulation resistance by water absorption. 

The nylons are hygroscopic. Figure 18.16 shows how the equilibrium water absorption of different nylons varies with humidity at room temperature. Figure 18.17 shows how the rate of moisture absorption is affected by the environmental conditions. 

Compared with aliphatic nylons it also shows greater rigidity and hardness, lower water absorption, low temperature coefficient of expansion, good resistance to heat and moisture, better electrical insulation properties, particularly under hot and damp condition, and of course transparency. 

Aminos. There are two basic types of amino plastics - urea formaldehyde and melamine formaldehyde. They are hard, rigid materials with good abrasion resistance and their mechanical characteristics are sufficiently good for continuous use at moderate temperatures (up to 100°C). Urea formaldehyde is relatively inexpensive but moisture absorption can result in poor dimensional stability. It is generally used for bottle caps, electrical switches, plugs, utensil handles and trays. Melamine formaldehyde has lower water absorption and improved temperature and chemical resistance. It is typically used for tableware, laminated worktops and electrical fittings. 

Certain chemicals (sorbents) have the ability to absorb moisture from a gas they may be either solid or liquid. Performance of a chemical dehumidifi cation device depends on the sorbent used. The sorbent must t>e able to attract and remove the sorbate, such as water, from the gas stream, Stirbems absorb water on the surface of the material by adsorption or by chemically combining with water (absorption). If the unit is regenerative, the process is reversible, allowing water to be removed. This is achieved by a sorbent such as silica gel, alumina gel, activated alumina, lithium chloride salt, lithium chloride solution, glycol solution, or molecular sieves. In the case of nonregenerative equipment, hygroscopic salts such as calcium chloride, urea, or sodium chloride are used. 

Moisture or water absorption is an important design property. It is particularly significant for a product that is used in conjunction with other materials that call for fits and clearances along with other close tolerance dimensions. 

Another major drawback of polysaccharides is their hydrophilic nature leading to low degrees of adhesion between fiber and matrix [11]. Moisture absorption takes place by three types of mechanisms namely diffusion, capillarity, and transport via micro cracks [2]. Among the three, diffusion is considered to be the major mechanism. Water absorption largely depends on the water-soluble or hygroscopic components embedded in the matrix, which acts as a semipermeable membrane. While, fiber/matrix adhesion and fiber architecture also affect the moisture absorption. The results of the water sorption experiment showed an interesting trend. The extent of water uptake was not very significant and also did not increase linearly with amount of filler (Table-2). 

When water is used as the immersion liquid, the test is essentially the ASTM Standard Test Method (D570) for Water Absorption of Plastics.( ) Determinations of the relative rate of water absorption are important in evaluating the effects of moisture exposure on such properties as mechanical strength, electrical resistivity, dielectric... 

Granulated fly ash [6] can substitute for Portland cement to an extent of 40% to 60%. Fly ash is used in granulated form and has a moisture content around 10% to 20%. The formulation can be used for cementing oil and gas wells within a temperature range of 20° to 250° C. The solution has reduced water absorption and increased sedimentation stability. A formulation [1388] is shown in Table 18-2. Hydrosil (Aerosil) is used to increase the adhesion of the produced cement rock to the casing string. It also reduces the density and water absorption. 

Texturization is not measured directly but is inferred from the degree of denaturation or decrease of solubility of proteins. The quantities are determined by the difference in rates of moisture uptake between the native protein and the texturized protein (Kilara, 1984), or by a dyebinding assay (Bradford, 1976). Protein denaturation may be measured by determining changes in heat capacity, but it is more practical to measure the amount of insoluble fractions and differences in solubility after physical treatment (Kilara, 1984). The different rates of water absorption are presumed to relate to the degree of texturization as texturized proteins absorb water at different rates. The insolubility test for denaturation is therefore sometimes used as substitute for direct measurement of texturization. Protein solubility is affected by surface hydrophobicity, which is directly related to the extent of protein-protein interactions, an intrinsic property of the denatured state of the proteins (Damodaran, 1989 Vojdani, 1996). 

An extremely useful technique for measuring the amount of size applied is non-contact on-line determination of water absorption [ 194]. The moisture content of sized warps can be derived from microwave absorption by the water present. 

Water absorption studies show that homopolymers II do not absorb moisture (to the nearest 0.1 % by weight), which is consistent with reported data on related polymer.3 Copolymers II absorb water in the range 0.6-5.3 wt%. 

The same functions used in agriculture can be applied to processed foods. In baked goods, wheat gluten, various additives, starch damage, and water absorption are just some of the parameters measured [21-24]. Dairy products are also important and often analyzed by NIR. Moisture, fat, protein, lactose, lactic acid, and ash are common analytes in the dairy industry [25-28]. 

Rigid PVC is an amorphous polymer with low shrinkage, a fair coefficient of thermal expansion for a polymer, limited creep at room temperature, and low water absorption by moisture exposure. 

Figure 4.51(a) compares the water absorption of several subfamilies of polyamides under the same conditions (low moisture). 

Relative humidity method. Water absorption is defined as the water absorbed by a dried protein powder with equilibration against water vapor at a known relative humidity. This method, also known as the equilibrium moisture content (EMC) method, was described first by Mellon et al. (10). Huffman et al. (11) used... 

Q The most detailed studies were reported by Hermansson and Akesson ( , 41) and Hermansson (42) in which the properties of a soy isolate, caseinate, WPC, and model test systems of additive and lean beef or pork were studied. Solubility, swelling, and viscosity (properties reviewed as related to water absorption) were correlated with moisture loss in the raw systems. In cooked systems, the best predictability of meat texture as affected by additive was a statistical model that included the functional properties of swelling and gel strength of protein additive dispersions. 

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