Water vapor permeation

This test is conducted on containers heat-sealed with foil laminate therefore, only the properties of the container are evaluated. The level of protection from water vapor permeation provided by a packaging system marketed with a heat-sealed foil laminate inner seal (up to the time the inner seal is removed) is expected to be approximately the same as that determined by this test. The acceptance criteria are those established in USP <671>. 

This test measures the water vapor permeation of a singleunit or unit-dose container closure system and establishes acceptance criteria for five standards (Class A-E containers). 

This test is intended for drugs being dispensed on prescription, but it has also been applied to the drug product manufacturer s container closure system. If the container closure system has an inner seal, it should be removed before testing. The results from this study reflect the contributions to water vapor permeation through the container and through the seal between the container and the closure. 

Gas Dehydration. It has been found that water vapor permeates cellulose acetate membranes at a rate approximately 500 times that of methane (Ref. 2). This exceptionally high selectivity for water vapor make cellulose acetate membrane systems attractive for dehydration of hydrocarbon gas streams to pipeline specifications on either a pure gas stream or while simultaneously removing contaminating acid gases. For these applications the small size, low weight and low maintenance of the SEPAREX system is particularly advantageous for offshore installations. 

Figure 4.19(b) shows an equivalent figure for a counter-flow module in which 5 % of the residue gas containing 100 ppm water vapor is expanded to 50 psia and introduced as a sweep gas. The water vapor concentration in the permeate gas at the end of the membrane then falls from 1900 ppm to 100 ppm, producing a dramatic increase in water vapor permeation through the membrane at the residue end of the module. The result is a two-thirds reduction in the size of the module. 

An alternative carrier-gas system uses a condensable gas, such as steam, as the carrier sweep fluid. One variant of this system is illustrated in Figure 9.7(d). Low-grade steam is often available at low cost, and, if the permeate is immiscible with the condensed carrier, water, it can be recovered by decantation. The condensed water will contain some dissolved organic and can be recycled to the evaporator and then to the permeate side of the module. This operating mode is limited to water-immiscible permeates and to feed streams for which contamination of the feed liquid by water vapor permeating from the sweep gas is not a problem. This idea has been discovered, rediscovered, and patented a number of times, but never used commercially [37,38], If the permeate is soluble in the condensable... 

Three standard tests for water vapor permeation have been established by the USP for use with solid oral dosage forms. 

The ability of a container closure system to protect against moisture can be ascertained by performing the USP (661) water vapor permeation test. The USP sets limits on the amount of moisture that can penetrate based upon the size and composition of the plastic components [HDPE, LDPE, or polyethylene terephthal-ate (PET)]. 

USP(661) hght transmission and water vapor permeation, container integrity (microbial ingress, dye penetration, hehum leak)... 

The mechanisms involved in the deterioration of insulation characteristics of LDPE are analogous to the principle of water vapor permeation through it. Two distinctively different paths can yield the water vapor permeability at the same value, i.e., many water molecules moving rather slowly or few molecules moving... 

An adiabatic membrane separation unit is used to dry (remove water vapor from) a gas mixture containing 10.0 mole% H20(v), 10.0 mole% CO, and the balance CO2. The gas enters the unit at 30 C and flows past a semipermeable membrane. Water vapor permeates through the membrane into an air stream. The dried gas leaves the separator at 30°C containing 2.0 mole% H20(v) and the balance CO and CO2. Air enters the separator at 50 C with an absolute humidity of 0.002 kg H20/kg dry air and leaves at 48 C. Negligible quantities of CO, CO2, O2, and N2 permeate through the membrane. All gas streams are at approximately 1 atm. 

The more conventional method for studying the energetics of diffusion in membranes is to perform permeation experiments as a function of equilibrium temperature. Figure 13 illustrates the eflEect of temperature on the apparent diflEusion coeflScient calculated from the water vapor permeation time lag established by steady-state permeation with a 75 to 0% RH gradient across the membrane. The principles of the time lag permeation method are adequately discussed elsewhere (58). The lower curve corresponds to a sample which was not mechanically supported and was observed to deform into a hemispherical shape. This deformation is the combined result of a small pressure diflEerence across the membrane and a decrease in modulus of stratum corneum as the temperature is increased. The upper curve corresponds to a supported sample. Previous to the experiment, both samples had identical thermal histories. Stresses accompanying deformation of the unsupported cor-... 

The other mechanism that rarely occurs in gas permeation is surface diffusion, where the vapor molecules (solutes) adsorb on to the surface of the pores and diffuse under a pressure gradient. This mechanism is neither likely to be dominant for noncondensable gases at low pressures and ambient temperatures, nor is it expected for water vapor permeation through hydrophobic materials [33]. 

The most common rubber polymers used in SVI closures are natural and butyl rubber (Table 9). Silicone and neoprene also are used but less frequently in sterile products. Butyl rubber has great advantages over natural rubber in that butyl rubber requires fewer additives, has low water vapor permeation properties, and has good characteristics with respect to gaseous (e.g., oxygen) permeation and reactivity with the active ingredient. 

T. Takeda, Mechanism of water vapor permeation through sugar coating layer [in Japanese], Yakuzaigaku 36, 216-221 (1976). 

A comparison of moisture vapor permeation through various polymers can be seen in Table 3.5. Notice that PCTFE is only second to FEP and both are among the most resistant plastics to water vapor permeation. Permeability data can be found in Appendixes I through IV. 

Films based on IPS, according to Gontard [9], the mechanical properties or barrier to water vapor unsatisfactory for practical applications, what became become worse under conditions of high humidity. Several studies have been made to improve the properties of the films based on IPS. It is reported that the addition of cross linking agents the film-forming solutions, or other physical methods, can improve the mechanical properties and/or the water vapor permeation (WVP) of films based on proteins [36]. Ou et al. [37] prepared films with 5.0 g of SPI, 3.0 g glycerol and different amounts (0, 50, 100, 150, 200 mg) of ferulic acid in two pH levels (8.0 and 9.0). At pH 9, the films showed better mechanical properties, as shown in Table 5.2. 

Membrane distillation is similar to pervaporation since phase change is involved in the process. When feed liquid (usually water) is in contact with a nonwetted porous hydrophobic membrane, water does not enter into the pores because the feed Hquid is maintained below a threshold pressure, the liquid penetration pressure of water. Only water vapor permeates through the pores from the feed to the permeate side. The driving force is the vapor pressure drop from the feed to the permeate side, since the permeate temperature is maintained below the feed temperature. Commercial hydrophobic membranes made of polypropylene, poly(vinylidene fluoride) and poly-... 

One of the important requirements of any packaging material is that it should not release any component into the drug product. Preparation of containers free of any leachables such as monomeric component is especially important for the containers of ophthalmics, parenteral products, and any liquid products. It was shown that di(2-ethylhexyl) phthalate was released from the PVC bags and that caused haziness of the taxol solution (37), USP/NF offers the protocol of chemical, spectral, and water vapor permeation tests and tolerances for plastic containers (55). Among those, chemical test is designed to give a quantitative assessment of the extractable materials in both organic solvents and water. 

The morphology, order, light transmittance and water vapor permeability of the A1 coated polypropylene films were reported in a previous publication [17], The films did not transmit light in tlie UV and visible region of the light spectrum and A1 coating reduced the water vapor permeation through the films [17],... 

The rate at which water vapor permeates through a plastic film or wall at a specified temperature and relative humidity (ASTM E96). 

Permatran-W, Water vapor permeation testing, MOCON/Modern Controls, Inc. 

Figure 1.4 (a) Oxygen and (b) water vapor permeation through polyurethane composites. Reproduced from Ref [8] with permission from American Chemical Society. 

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