Permeability of membranes to water vapor with special reference to packaging materials/

Abstract

A study of data from about 30 sources in the literature shows that measurements of the permeability of membranes to water vapor have been made by four types of methods, with many modifications, and that the testing conditions have varied widely. The test period ranged from 2 to 2,000 hours; the temperature from-14 to 45°C; the area of the specimen from 0.15 to 323 cm 2 ; and the vaporpressure difference from to 72 mm of Hg. Considerable variety was also found in methods of sealing on the specimen, ventilation of the specimen, and units of expressing the results. Data have been reported in at least 20 units. Sheet materials used in packaging commodities range in permeability to water vapor from that of waxes and rubber to that of textile fabrics. The data indicate that the transpiration of moisture is proportioual to the area, to the time in the steady-state region, and, within certain limits, to the difference in vapor pressure. It is reported by some to be inversely proportional to the thickness also, while others disagree. A seal to* prevent edge leakage is of the utmost importance. Temperature requires close control. Relative humidity, especially at high values, and the slowness of diffusion of water vapor through air have a marked influence in many cases. Suggested mechanisms of moisture transpiration include consideration of gaseous diffusion, diffusion of moisture in solid solution, movement of moisture as a function of the content of hygroscopic moisture, and migration of adsorbed water along surfaces.

Thinking-with Decorator Crabs: Oceanic Feminism and Material Remediation in the Multispecies Aquarium

“…To sense this world of waters known to the creatures of the sea we must shed our human perceptions of length and breadth and time and place, and enter vicariously into a universe of all-pervading water. (Carson, 2018(Carson, [1937, p. 63) Our intention for this article was to explore a material feminist ethics of care within the context of the oceanic turn. Enclosed in the sparkling, shifting potentialities of marine worlds, we approached the project as an opportunity to dismantle terrestrial hierarchies implicit within the Anthropocene, to think-with the decorator crabs.…”

“…Neither you nor I, with our earth-bound senses, know the foam and surge of the tide that beats over the crab hiding under the seaweed of his tide-pool home; or the lilt of the long, slow swells of mid-ocean. (Carson, 2018(Carson, [1937, p. 63)…”

Green Chemistry in Medical Applications: Preliminary Assessment of Kuzu Starch Films with Plant-Based Antiseptics

“…In 1937, Frederick Carson suggested that the mechanism of moisture transpiration through various materials involves the diffusion of gases and water molecules, the movement of moisture as a function of the hygroscopic moisture content, and the migration of adsorbed water along internal surfaces [55]. This clearly indicates a direct dependence of the ability to transmit water on the physicochemical properties of the material, including its density, the degree of "throughput" of internal spaces, and hydrophilicity.…”

A study of the national humidity and moisture measurement system

“…NBS humidity measurement capabilities Concurrent with supplying measurement services, NBS has also been a user of the humidity and moisture measurement system in discharging its responsibilities and in performing its scientific and technological work. This activity has covered a wide range of investigations such as studying the effect of humidity on resistance of standard electrical resistors [135], paper [136][137][138], fibers and textiles [139-U2], plastics [US-US], collagen, hide and leather [147][148][149][150][151], microchemical balances [152], engines [153], asphalt [154], air conditioning [155], ionization measurements [156], and floor coverings [157].…”