Permeability rate

To apply these package criteria to polymer properties, a conversion was made based on a 10-12 oz. container with a surface area-to-volume ratio of 4.0 (in.2/oz.) and an average wall thickness of 0.030 in. The oxygen, carbon dioxide, and water permeability rates needed to meet these high barrier criteria over a six month shelf life are shown in Table III. Larger container sizes—16, 32, 48 oz. etc.—would permit slightly higher permeability factors for the same bottle criteria, because of their lower ratio of surface-to-volume. 

Formulation Apparent permeability rate constant, kp SE, h 1 First-order dissolution rate constant, kd SE, h-1 = SE... 

Using liposomes made from phospholipids as models of membrane barriers, Chakrabarti and Deamer [417] characterized the permeabilities of several amino acids and simple ions. Phosphate, sodium and potassium ions displayed effective permeabilities 0.1-1.0 x 10 12 cm/s. Hydrophilic amino acids permeated membranes with coefficients 5.1-5.7 x 10 12 cm/s. More lipophilic amino acids indicated values of 250 -10 x 10-12 cm/s. The investigators proposed that the extremely low permeability rates observed for the polar molecules must be controlled by bilayer fluctuations and transient defects, rather than normal partitioning behavior and Born energy barriers. More recently, similar magnitude values of permeabilities were measured for a series of enkephalin peptides [418]. 

BCS Class III High-solubility, low-permeability drugs. Absorption is permeability-rate limited but dissolution will most likely occur very rapidly. For this reason,... 

Recently it has been claimed that the tissue can be considered viable if the drug permeability does not change over the course of the experiment, and thus the actual permeability experiments themselves may provide insight into the viability of the tissue [109, 157], This method was employed in permeation experiments using porcine buccal mucosa, where the permeability of compounds was assessed in two consecutive permeability experiments to ensure the nature of the barrier was not compromised [111, 112]. While this demonstrates that the barrier nature of the tissue was unaltered between the permeation experiments, the tissue may have already undergone tissue death in the time between the excision and the commencement of the initial permeation experiment, and thus the permeability rate obtained in vitro may not be representative of the in vivo situation. Therefore, more studies assessing the dependence of the barrier nature of the buccal mucosa on tissue viability are... 

Two similar approaches were adopted by Ishihara et al. [364-368]. Membranes based on hydroxyethyl acrylate, dimethylaminoethyl methacrylate and trimethyl silyl styrene were solvent cast, and capsules containing insulin and glucose oxidase were prepared by interfacial precipitations. The authors reported dramatic changes in permeability in response to pH changes between 6.1 and 6.2. Moreover, addition of glucose induced an increase in the permeation rate of insulin, and upon removal of the glucose the permeability rates returned to their original levels. However, the conclusions were criticized [361] due to... 

Table 8—Permeability rate of propranolol hydrochloride from Methocel matrix diffusion study through hairless mouse skin (comparative data)...

Table V. Comparative Permeability Rate Data - WEC Vs Vendor...

From the previous discussion it can be seen that, if component i is the more permeable, increasing Pf1, either by increasing the total pressure or the concentration of component i, will result in a higher membrane permeability rate. In addition, higher values for ai/j result in greater efficiency in gas separation. 

Fig. 17.5 Schematic representation of a physiological based model. Left figure shows the physiological structure, upper right figure shows a model for a perfusion rate limited tissue, and lower right figure shows a model for a permeability rate-limited tissue. Q denotes the blood flow, CL the excretion rate, KP the tissuerplasma distribution coefficient, and PS the permeability surface area coefficient.

BUNA N (nitrile) Aromatic hydrocarbons, dilute acids and bases, silicones, helium hydrogen Halogen compounds, halogenated hydrocarbons (carbon tetrachloride, trichlorethylene), ketones (acetone), nitro compounds, or strong acids Typical color black. Temperature range -50 to 120°C. Easily compressed. Density 1.00. Lowest permeability rates for gases of all elastomers. 0.25... 

Tests at 1000°C. After 1 hour of pumping the apparent leak rate of a mullite double-walled vessel is 1.7 X 10 8 l.-mm. of mercury per second or 2 X 10-8 cc. (N.T.P.) per second. In terms of permeability rates this value is equivalent to 3 X 10-10 cc./sq. cm./second/mm./cm. of mercury. Roeser (28) has studied a number of refractory procelain tubes from several manufacturers. His permeability values vary from 8.3 X 10 10 to 5 X 10-8 cc./sq. cm./second/mm./cm. of mercury. We have studied two double-walled vessels. These two tubes give nearly identical apparent leak rates although one is constructed of mullite and the other from zircon. It may be possible that more sensitive tests would show up differences in apparent leak rates. 

Transport by facilitated diffusion A large number of molecules and ions were shown to permeate membranes considerably faster than expected from their lipid-water partitioning behavior. This led to the recognition of additional transport mechanisms. Systematic investigations of permeability rates in membranes, reconstituted membranes, and membrane models as functions of the temperature of the nature and concentration of the permeant in the absence and in the presence of additives, suggested three different facilitated passive transport mechanisms ... 

Polymer materials, modified with layered silicate nanoparticles, have some significant advantages. For example, introducing Na-montmorrillonite into polymer matrix increases initial modulus, tensile strength, thermal stability and fire resistance, reduces gas permeability rate of material. 

For carrier-mediated transport of L-lactic acid across human carcinoma cell line, it was found that increasing agitation rate resulted in a larger fractal dimension accompanied by a decrease in the substrate permeability rate. The classical Michaelis-Menten model is known to be only valid for a limited range of glucose concentrations. An alternative model was proposed including convective and non-linear diffusive mechanisms corresponding to the first and second (fractal power function) terms in Eq. (30). 

Ward and co-workers adapted this technique to the preparation of ultrathin slllcone/polycarbonate membranes and advanced it by spreading the dilute solution first on a limited water surface between two plastic blocks and then moving the blocks apart. This method spreads the polymer solution continuously, reducing the thickness of the film. A nitrogen permeability rate of 8.6 x 10 cm (STP)/cm -s-emHg and an 0 /N selectivity of 2.3 are reported for a 1000 X thin film. 

According to Table III, the contribution of the silicone layer to the flow of the less permeable carbon monoxide Is only 1.2% and can be neglected, but it does contribute remarkably to the flow of the more permeable hydrogen by approximately 20%. Correspondingly, the H /CO separation factor of the selective polysulfone skin-layer is reduced by 20% from 40 to 33, because the ideal separation factor is by definition the ratio of the permeability rates or - vice versa - the reciprocal of the ratio of the flow resistances. With this invention, Henis and Tripodi discovered a simple and ingenious solution to the problem of surface porosity. They found a limiting value for the surface porosity. If it exceeds the value of 10, ... 

Table IV Pure gas permeability rates of commercial reverse osmosis membranes at 25°C and 40 bar...

Q Membrane polymer Manufacturer Permeability Rate 1) Ideal Separation Factor ... 

The most Important requirements of high selectivity and high permeability for the more permeable CO. gas seem to be met by the asymmetric CA blend membranes. They elnilblt the permeability rates of rubbery materials and the selectlvities of a glassy polymer with an Intermediate high glass transition temperature. 

Permeability rate, PA, as a function of sublimation temperature, T, during the freeze-drying of CA blend membranes (pure gases, 25 C, 40 bar to obtain... 

Solvent-drying. After annealing at lOO C, the absorbed water inside the membranes was removed by a proprietary procedure. Its effect on gas permeation is given in Table VI. No effect is observed on the.helium and carbon dioxide permeability rates. But the permeability rates of nitrogen and methane are considerably lowered so that the separations of both systems, helium/nltrogen and carbon dloxlde/methane, are enhanced. With a value of 44.1 for helium/ nitrogen, the ideal separation factor of the external reference membrane is slightly exceeded, whereas the separation factor for CO2/CK of more than 2500 is Improved by a factor of 600. 

It is evident that the permeability rates of gases similar in size and shape like nitrogen and methane depend on the actual state of the polymers. The transformation of gelled polymers to solids by the drying procedure may change their state in such a manner that the polymer density increases and the "free volume" decreases resulting in lowered permeability rates. Exceptions from this general rule apply only for molecules such as helium which are very small and carbon dioxide which are able to plasticize the CA polymers. 

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