Moisture absorbers

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. 

Moisture Absorbency. PVA fiber is more hygroscopic than any other synthetic fiber. The hygroscopicity varies depending on how the fiber is processed after spinning, ie, in heat-drawing, he at-treatment, acetalization, and the like. 

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... 

Moisture. Absorbed and retained moisture, especially as ice, has a significant effect on the stmctural and thermal properties of insulation materials. Most closed-ceU plastic foams have low permeance properties most notably where natural or bonded low permeance surface skins exist (29,30). Design, building, and constmction practices requite adequate vapor retarders, skins, coatings, sealants, etc, in order to prevent the presence of moisture. However, moisture vapor cannot be completely excluded, thus the possibiUty of moisture absorption and retention is always present. The freezing of moisture and mpturing of cells result in permanent reduction of thermal and stmctural performance. 

Fibers. Polypropylene fibers are extensively used in carpeting. Bulked continuous filament yams are commonly used in carpet facing in the level loop carpets used in commercial buildings however, nylon remains the dominant face yam in tufted household carpets. The advantages of polypropylene carpeting are superior stain resistance and low moisture absorbance. Polypropylene sHt tape fibers are heavily used in carpet backing. 

Automated soldering operations can subject the mol ding to considerable heating, and adequate heat deflection characteristics ate an important property of the plastics that ate used. Flame retardants (qv) also ate often incorporated as additives. When service is to be in a humid environment, it is important that plastics having low moisture absorbance be used. Mol ding precision and dimensional stabiUty, which requites low linear coefficients of thermal expansion and high modulus values, ate key parameters in high density fine-pitch interconnect devices. 

Electric hygrometers measure the electrical resistance of a film of moisture-absorbing materials exposed to the gas. A wide variety of sensing elements have been used. 

The gravimetric method is accepted as the most accurate humidity-measuring technique. In this method a known quantity of gas is passed over a moisture-absorbing chemical such as phosphorus pent-oxide, and the increase in weight is determined. 

Moisture. The presence of water in a filler is not usually beneficial. Most fillers added to adhesives have a moisture content lower than 1 wt%. Only precipitated silicas and sepiolite contain about 5-10 wt% moisture. For some applications, fillers must be completely dried to exhibit adequate performance. Moisture absorbed on the surface of fillers impacts the rate and extent of curing of rubber base adhesives. 

Moisture absorbed by 2.0g of CP K nitrate at 25° as a function of fineness is shown below ... 

Moisture absorbents or desiccants are required. These are spread on trays and distributed throughout the boiler, so that circulating air passes over them. Quick lime (CaO) is used at 8 to 10 lb for every 1,000 lb/hr of steaming capacity. Alternatively, silica gel is used at 4 to 6 lb per 1,000 lb of steaming capacity. 

The absorption of moisture critically affects other important resin properties, particularly those associated with low-dielectric and thermomechanical applications. Results of a 96-h boiling water immersion test are presented in Table 2.2. The moisture absorbed decreased substantially with fluoromethylene chain length from n = 3 to n = 6, followed by only modest decreases for n = 8 and 10. This latter behavior was somewhat unexpected and may be the effect of decreased cross-link density counteracting the increased fluorine content. These 100°C measurements are just above the glass transition and the situation may be different at room temperature. These measurements are in progress. 

Moisture absorption. Directly related to the atoms making up the polymer. The more moisture-absorbing the molecule, the less dimensional stability strength, stiffness, electrical properties are also adversely affected. 

Mix in moisture-absorbing materiais, such as newspaper, egg cartons, paper toweis, and cardboard tubes. Add a sprinkiing of iimestone and ciear any drainage hoies. If on investigation you cannot see any active worms at aii, you wiii have to assume that they are dead. Ciear out the bin and start again. 

Most anionic (as well as cationic) polymerizations are carried out in an inert atmosphere with rigorously cleaned reagents and glassware since trace impurities lead to termination [Hadji-christidis et al., 2000]. Moisture absorbed on the surface of glassware is usually removed by... 

Yencho then constructed the initial version of the machine and explored the parameters necessary to successfully form flaw-free parts. A key finding concerned the effects of trapped moisture. Despite the generally hydrophobic nature of PEEK, it was found that small amounts of moisture absorbed by the Gr/PEEK laminates subsequent to their manufacture converted into steam during the forming operation and caused extensive delamination. This was in... 

Table 2.8 Relative humectancy of sucrose, glucose and lactose (% moisture absorbed at 20°C)...

Kreyenbuhl and Sartorius [55] found that this exchange proceeds slowly if the moisture content is less than 1 %. If it is 1 % or more so, the exchange is complete after 3-6 months and is accompanied by decreased explosive power. The addition of a moisture absorbent (e.g. urea resin foam) inhibits this exchange (French explosive Noburex, p. 552). 

The exposed sample is then reweighed and the moisture absorbed is expressed as % hygroscopicity... 

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