Moisture transmission

Thermal Insulation. Foamed plastics (qv) are used as thermal insulation for aU types of constmction because of their low heat- and moisture-transmission values. Polystyrene is used either as foamed board or expandable beads. The foam may be faced with a stmctural surfacing material, eg, a kraft liner-board, to form a panel for insulating mobile homes. These foams can dupHcate the appearance of wood and be used as trim. Foams can also be used as backing, for example, on aluminum siding, to provide heat and sound insulation. Foamed beads can be incorporated in concrete to reduce its density and provide some thermal insulation. 

The self-adhesive tape coatings are thin and the adhesive itself does not necessarily come into contact with the valleys in the cleaned metal surface. Under these circumstances, the transmission of water vapour through the film to the metal may be possible. Moisture-transmission characteristics and other properties of p.v.c. and polyethylene tapes, as given by major manufacturers, are provided in Table 14.6. 

Provides some barrier to moisture transmission. Used in sealing layers. 

Provides some barrier to moisture transmission. Used in sealing layers. Main benefits with films are for increased tear and puncture resistance. 

Provides barrier to moisture transmission and tear resistance to films. 

Provides excellent barrier to oxygen and moisture transmission. 

Lower oxygen permeability and reduced moisture transmission... 

Table 4.14. Comparison of Moisture Transmission through Foiis.

Moisture greatly influences the performance and durability of building materials. and thus moisture transmission is an important consideration in the con-slmction and maintenance of buildings. 

The unit dose is either glass or plastic, with the use of plastic form-fill-seal equipment being dominant. However, glass is considered more elegant pharmaceutically in some markets, and can be terminally sterilised where this is a requirement. With form-fill-seal processes, a strip of ampoules is produced, with the neck being much easier to break than glass. The plastic is pervious to moisture transmission, which will occur on storage, especially in dry environments thus an aluminium overwrap may be necessary. 

The chlorinated tetrafluoroethylene (CTFE) fluoropolymer Aclar from Allied Corporation is one of the highest barrier materials against moisture transmission. It is used in an antibiotic test kit where even trace amounts of moisture would violate the accuracy of the test. 

The films were biaxially oriented at ratios of 3 1-8 1. They had low moisture transmission rate, toughness, abrasion resistance, good clarity and gloss, suitable as moisture barrier packaging for food, pharmaceuticals, and electronics... 

Millad 3988 clarifier is used to produce coextruded blown PP film at 15% lower cost. In comparison with BOPP, blown PP film has improved haze values, gloss, stiffness, and moisture transmission rates. Ingenia Polymers manufactures a high-clarity antiblock mas-terbatch for PE blown film that produces lower haze than conventional diatomaceous earth antiblocks commonly used for blown film (13.5%, at loadings from 1500 to 15,000 ppm compared to haze of 9-19% for diatomaceous earth). ... 

The vinyl ester resins are the most corrosion resistant of any of the monolithic surfacing systems, and they are also the most expensive and difficult to install. They are used when extremely corrosive conditions are present. The finished flooring is vulnerable to hydrostatic pressure and vapor moisture transmission. Refer to Table 18.5 for their resistance to atmospheric corrosion and Table 18.10 for their resistance to selected corrodents. 

Acrylic monolithic coatings are suitable for interior or exterior applications with relatively benign atmospheric exposures. Refer to Table 18.5. They excel at water and weather resistance, and are best at breathing in the presence of a moisture transmissive problem in the slab. They are intended for protection against moderate corrosion environments. The advantages for their use are as follows ... 

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