Moisture impermeability

Once applied, the eure rate will depend heavily on the moisture eontent and/or moisture vapor permeability of the substrates between whieh the adhesive is sandwiehed. For wood substrates, typieally full eure oecurs in a day with the faster systems. Misting of the substrates with water is sometimes conducted prior to adhesive applieation to further speed eure, or when the substrates are substantially moisture impermeable. 

Dioxime cures yield vulcanisates with good ozone resistance and moisture impermeability and, as such, are frequently used for curing electrical insulating compounds. 

Rico-Pena, D.C., and Torres, J.A. (1990). Edible methylcellulose-based films as moisture impermeable barriers in sundae ice cream cones. J. Food Sci. 55, 1468-1469. 

Because LDPE is so pliable, it is not typically used for rigid containers or for films. HDPE is much more rigid, but both compounds are often employed in squeeze bottles and other flexible applications. PE may be used as a moisture-impermeable layer of a multilayer film for sealing blister containers. It may also be used for producing sealable envelopes in which pharmacists can dispense moisture-sensitive powders or tablets. Care should be taken to assure that PE additives do not leach into the pharmaceutical substance. ... 

Dry place Average relative humidity (RHave) < 40% at CRT (or equivalent moisture at other temperatures) excursions of up to 45% are permitted as long as RHave remains below 40% storage in a moisture impermeable container is sufficient... 

Such adhesives are not suitable for extensive bonded joints of moisture impermeable materials with regularly applied adhesive layers, since curing is not possible. In such cases the two-component systems or, if possible, additional moisturization, as mentioned before, is recommended. 

For moisture-impermeable adherends only suitable if water addition (spraying, booster) is possible or adhesive application occurs in wave or line form to enable air access. 

Chlorinated and particularly fluorinated derivatives of ethylene usually offer high inertness and good barrier properties. One film, Aclar (trade name) based on polymonochlorotrifluoroethylene (PCTFE), is the most moisture-impermeable commercial film currently known. For a similar thickness it is approximately ten times less permeable than PVdC. Derivatives generally have high melting and softening points. Found both as homopolymers and copolymers. For detail see Chapter 13. 

Nowadays, amorphous silicon dioxide may be used as corrosion-resistant coatings in various types of cans and as moisture-impermeable films, as well as for rheology control in materials such as paints, silicone rubbers, polyester compounds, dental formulations, emulsions, cosmetics, and excipients in pharmaceuticals. 

Most of the traditional IM meat products have evolved from natural drying of the meat mixture. In the drying process, the ultimate water activity a ) of IM meat approaches 0.60 to 0.90, which is equivalent to a relative humidity (RH) of 60-90% at ambient temperature (Leistner, 1987). The products do not require either strict moisture impermeable packaging or refrigeration during storage. Indeed the products are processed and dried to a stable state and can be kept at ambient temperatures without spoiling. 

Numerical calculations are carried out for cylindrical samples made of kaolin and placed on moisture impermeable plate at the bottom (Figure 62.9). 

FIGURE 62.9 Convective drying of cylindrical sample placed on moisture impermeable plate. 

Uses Butyl mbber in sealants, coatings, elec, encapsulating compds., and conformal coatings incl. moisture-impermeable coatings, marine and constmetion sealants, elec, encapsulants tackifier for pressure-sensi-... 

Tar-based products are used in conjunction with polymers in the manufacture of polymer-reinforced membranes which are biostable and moisture impermeable. In this combination, polymer (polyurethane or some styrene-containing block copolymers) offers reinforcing network but it is also plasticized to produce elastomeric materials having excellent... 

The original intent of this project was to identify and/or perfect vendor-supplied, state-of-the-art hydro-phobic polymer sealants, such that the end product could meet military criteria for hermeticity in hybrid microelectronic devices. Solubility and diffusivity constants and permeabilities for several types of hydrophobic polymers were determined. Data from the laboratory and theory from literature both indicate that moisture impermeable polymers are not attainable, at least to meet military standards. The project objective was then redirected towards finding a means of passivating the surface of a microelectronic device against moisture. It was found that interface modification, i.e., passivation of the chemically reactive surface species, provides significant protection in high temperature and humidity environments. Plasma polymerization of hexamethyIdi-silazane (HMDS) afforded phenomenal protection to moisture sensitive thin film nichrome resistors even under the most severe test conditions. 

Recently more and more attention has been paid to atmosphere-resistant and moisture-impermeable coating materials [205], for example, in apparatus construction (instrument making), enamels constituting copolymers of vinylchloride with vinyracetate in agriculture,alkyd-styrene enamels and for the painting of light motor vehicles [206], polyacrylate enamels. 

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