Water vapor, properties

Mechanical and Water Vapor Properties of Gelatin-Based Films as Function of Relative Humidity, Temperature, and Film Thickness... 

Mechanical and Water Vapor Properties of Gelatin-Based Films... 

These blends (introduced in 1958 40 wt.% PIB) were developed to enhance the low-temperature mechanical performance (especially flexibility and impact strength). Since PIB is miscible with both, PP and LLDPE, soon the three-component blends were developed. They also showed good water vapor properties, and high UV resistance [4]. 

The 1 1 blends ate flexible, resistant to cracking under stress, show good water-vapor properties. The blends are formulated for extrusion, injection, and blow molding. Ute weld-line strength, resistance to warp e and shrinkage depend on processing conditions. ... 

It possesses outstanding barrier properties to gases, especially water vapor. It is surpassed only by the fully fiuorinated polymers in chemical resistance. A few solvents dissolve it at temperatures... 

The choice of the solvent also has a profound influence on the observed sonochemistry. The effect of vapor pressure has already been mentioned. Other Hquid properties, such as surface tension and viscosity, wiU alter the threshold of cavitation, but this is generaUy a minor concern. The chemical reactivity of the solvent is often much more important. No solvent is inert under the high temperature conditions of cavitation (50). One may minimize this problem, however, by using robust solvents that have low vapor pressures so as to minimize their concentration in the vapor phase of the cavitation event. Alternatively, one may wish to take advantage of such secondary reactions, for example, by using halocarbons for sonochemical halogenations. With ultrasonic irradiations in water, the observed aqueous sonochemistry is dominated by secondary reactions of OH- and H- formed from the sonolysis of water vapor in the cavitation zone (51—53). 

Acrylonitrile—methyl acrylate—iadene terpolymers, by themselves, or ia blends with acrylonitrile—methyl acrylate copolymers, exhibit even lower oxygen and water permeation rates than the iadene-free copolymers (110,111). Terpolymers of acrylonitrile with iadene and isobutjlenealso exhibit excellent barrier properties (112), and permeation of gas and water vapor through acrylonitrile—styrene—isobutjleneterpolymers is also low (113,114). 

Psychrometrics. Psychrometrics is the branch of thermodynamics that deals specifically with moist air, a biaary mixture of dry air and water vapor. The properties of moist air are frequentiy presented on psychrometric charts such as that shown ia Figure 2 for the normal air conditioning range at atmospheric pressure. Similar charts exist for temperatures below 0°C and above 50°C as well as for other barometric pressures. AH mass properties ate related to the mass of the dry air. 

Linear Low Density Polyethylene. Films from linear low density polyethylene (LLDPE) resias have 75% higher tensile strength, 50% higher elongation-to-break strength, and a slightly higher but broader heat-seal initiation temperature than do films from LDPE. Impact and puncture resistance are also improved over LDPE. Water-vapor and gas-permeation properties are similar to those of LDPE films. 

OPP producers have expanded the core, creating a foam stmcture with lower density, greater opacity, and a stiffer, more paper-Hke feel. Vacuum metallisation increases opacity and water-vapor barrier properties. 

Oriented polypropylene film has exceUent water-vapor barrier but poor gas barrier properties exceUent clarity, or opacity in newer forms and good heat-seal properties in packagiag appHcations. 

Polyester. Poly(ethylene terephthalate) [25038-59-9] (PET) polyester film has intermediate gas- and water- vapor barrier properties, very high tensile and impact strengths, and high temperature resistance (see Polyesters, thermoplastic). AppHcations include use as an outer web in laminations to protect aluminum foil. It is coated with PVDC to function as the flat or sealing web for vacuum/gas flush packaged processed meat, cheese, or fresh pasta. 

Of the common commercial resias and films, PVDC has the best water-vapor and oxygen-barrier properties. High crystallinity confers resistance to the permeation of odors and flavors, as weU as to fat and oil. Because of its high chloride content, PVDC tends to corrode processing equipment, which increases manufacturing costs. Unlike other high oxygen-barrier materials, PVDC is almost insensitive to water and water vapor. 

Ethylene vinyl acetate copolymer (EVA) forms a soft, tacky film with good water-vapor barrier but very poor gas-barrier properties. It is widely used as a low temperature initiation and broad-range, heat-sealing medium. The film also serves for lamination to other substrates for heat-sealing purposes. 

Polyacrylonitrile (PAN) films have outstanding oxygen and CO2 barrier properties, but only modest water-vapor barrier properties. They are for processed-meat and fresh pasta packaging laminations where an oxygen barrier is required for vacuum or gas flush packaging. 

To enhance water-vapor- or gas-barrier properties, layers of different plastics may be injected together or sequentially. Multilayer injection-molded pieces may be prepared as packaging or for blowing into bottle or jar shapes. 

Ferritic stainless steels depend on chromium for high temperature corrosion resistance. A Cr202 scale may form on an alloy above 600°C when the chromium content is ca 13 wt % (36,37). This scale has excellent protective properties and occurs iu the form of a very thin layer containing up to 2 wt % iron. At chromium contents above 19 wt % the metal loss owiag to oxidation at 950°C is quite small. Such alloys also are quite resistant to attack by water vapor at 600°C (38). Isothermal oxidation resistance for some ferritic stainless steels has been reported after 10,000 h at 815°C (39). Grades 410 and 430, with 11.5—13.5 wt % Cr and 14—18 wt % Cr, respectively, behaved significandy better than type 409 which has a chromium content of 11 wt %. 

Sihcon dioxide layers can be formed using any of several techniques, including thermal oxidation of siUcon, wet anodization, CVD, or plasma oxidation. Thermal oxidation is the dominant procedure used in IC fabrication. The oxidation process selected depends on the thickness and properties of the desired oxide layer. Thin oxides are formed in dry oxygen, whereas thick (>0.5 jim) oxide layers are formed in a water vapor atmosphere (13). 

BiaxiaHy orieated PPS film is transpareat and nearly colorless. It has low permeability to water vapor, carbon dioxide, and oxygen. PPS film has a low coefficient of hygroscopic expansion and a low dissipation factor, making it a candidate material for information storage devices and for thin-film capacitors. Chemical and thermal stability of PPS film derives from inherent resia properties. PPS films exposed to tolueae or chloroform for 8 weeks retaia 75% of theh original streagth. The UL temperature iadex rating of PPS film is 160°C for mechanical appHcatioas and 180°C for electrical appHcations. Table 9 summarizes the properties of PPS film. 

Wire cords are particularly subject to degradation of their adhesion values by moisture. To combat this, halogenated butyl (HIIR) is used in tire innerliners because of its property of low air and water vapor diffusion rates. Moisture is present in most air pumps and many tires are mounted with water left in the tire on mounting. For these reasons tires and tire compounds are tested extensively at simulated aging conditions in the laboratory and on test vehicles before they are sold to the customer. 

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