Permeation properties

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. 

Pervaporation has been commercialized for two appHcations. The first and most developed is the separation of water from concentrated alcohol solutions. GFT of Neunkirchen, Germany, the leader in this field, installed their first important plant in 1982. More than 100 plants have been installed by GFT for this appHcation (90). The second appHcation is the separation of small amounts of organic solvents from contaminated water (91). In both of these apphcations, organics are separated from water. This separation is relatively easy, because organic compounds and water, due to their difference in polarity, exhibit distinct membrane permeation properties. The separation is also amenable to membrane pervaporation because the feed solutions are relatively nonaggressive and do not chemically degrade the membrane. 

Films or membranes of silkworm silk have been produced by air-drying aqueous solutions prepared from the concentrated salts, followed by dialysis (11,28). The films, which are water soluble, generally contain silk in the silk I conformation with a significant content of random coil. Many different treatments have been used to modify these films to decrease their water solubiUty by converting silk I to silk II in a process found usehil for enzyme entrapment (28). Silk membranes have also been cast from fibroin solutions and characterized for permeation properties. Oxygen and water vapor transmission rates were dependent on the exposure conditions to methanol to faciUtate the conversion to silk II (29). Thin monolayer films have been formed from solubilized silkworm silk using Langmuir techniques to faciUtate stmctural characterization of the protein (30). ResolubiLized silkworm cocoon silk has been spun into fibers (31), as have recombinant silkworm silks (32). 

Binding and Permeation Properties of the LamB Channel for Different Sugars ... 

Plastics packaging and contained food products are chemically related in four distinct ways. This relationship is based largely on the permeation property of the plastic material. Direct chemical reaction between plastic and product is seldom a problem when inert plastics such as polyethylene are used. However, polyethylene can transmit minute amounts of product to the outside. This paper examines the effect of permeation through the plastic wall and the direct effects of the plastic on the food product. Specific food packaging applications and methods of testing are discussed. 

The chemical modification of poly (2,6-dimethyl-l,4-phenylene oxide) (PPO) by several polymer analogous reactions is presented. The chemical modification was accomplished by the electrophilic substitution reactions such as bromination, sulfonylation and acylation. The permeability to gases of the PPO and of the resulting modified polymers is discussed. Very good permeation properties to gases, better than for PPO were obtained for the modified structures. The thermal behavior of the substituted polymers resembled more or less the properties of the parent polymer while their solution behavior exhibited considerable differences. 

In our research, three chemical modification approaches were investigated bromination, sulfonylation, and acylation on the aromatic ring. The specific objective of this paper is to present the chemical modification on the PPO backbone by a variety of electrophilic substitution reactions and to examine the features that distinguish modified PPO from unmodified PPO with respect to gas permeation properties, polymer solubility and thermal behavior. 

The solution properties of the brominated PPO derivatives were similar to those of the parent polymer. The gas permeation properties of PPO and PPO containing between 6.5% to 100% Br groups per repeat unit are summarized in Table I. 

The permeation properties of substituted PPO to a carbon dioxide, methane, nitrogen mixture were studied for several systems. The results are presented in Table VI. 

Chemical modifications of PPO by electrophilic substitution of the aromatic backbone provided a variety of new structures with improved gas permeation characteristics. It was found that the substitution degree, main chain rigidity, the bulkiness and flexibility of the side chains and the polarity of the side chains are major parameters controlling the gas permeation properties of the polymer membrane. The broad range of solvents available for the modified structures enhances the possibility of facile preparation of PPO based membrane systems for use in gas separations. 

The fluid mosaic model conveniently describes how the constituent molecules are ordered, and it correctly describes, in first order, some of the membrane s properties. However, it does not give explicit insight into why the biological membrane has a particular structure, and how this depends on the properties of the constituent molecules and the physicochemical conditions surrounding it. For this reason, only qualitative and no quantitative use can be made of this model as it pertains to permeation properties, for example. It is instructive to review the physicochemical principles that are responsible for typical membrane characteristics. In such a survey, it is necessary to discuss simplified cases of self-assembly first, before the complexity of the biological system may be understood. The focus of this quest for principles will therefore be more on the level of the molecular nature of the membrane, rather than viewing a... 

In this review, we have presented a molecular picture of the lipid bilayer system in relation to its permeation properties, as it appears from simulations and from self-consistent field calculations. Of course, it was not possible to go into all the details. In fact, the practicalities are always much more complicated, and the fine details are only of interest to the experts. 

Leermakers, F. A. M. and Kleijn, J. M. (2004). Molecular modelling of biological membranes. Structure and permeation properties. In Physicochemical Kinetics and Transport at Biointerfaces, eds. van Leeuwen, H. P. and Koster, W., Vol. 9, IUPAC Series on Analytical and Physical Chemistry of Environmental Systems, Series eds. Buffle, J. and van Leeuwen, H. P., John Wiley Sons, Ltd, Chichester, pp. 15-111. 

Chen LL, Chetty DJ, Chien YW (1999) A mechanistic analysis to characterize oramucosal permeation properties. Int J Pharm 184 63-72... 

Sakai, T., Takenaka, H., Wakabayashi, N., Kawami, Y. and Torikai, E. 1985. Gas permeation properties of solid polymer electrolyte (SPE) membranes. Journal of... 

Broka, K. and Ekdunge, P. 1997. Oxygen and hydrogen permeation properties and water uptake of Nation 117 membrane and recast film for PEM fuel cell. Journal of Applied Electrochemistry 27 117-123. 

Hietala, S., Skou, E. and Sundhokn, F. 1999. Gas permeation properties of radiation-grafted and sulfonated poly-(vinylidene fluoride) membranes. Polymer 40 5567-5573. 

Zhou, W, Watari, T., Kita, H. and Okamoto, K. 2002. Gas permeation properties of flexible pyrolytic membranes from sulfonated polyimides. Chemistry Letters 5 534-535. 

Kita, H., Fuchida, K., Hority, T., Asamura, H., and Okamoto, K. (2001) Preparation of faujasite membranes and their permeation properties. Sep. Purif. Tech., 25, 251-258. 

Gas permeation properties of ethylene vinyl acetate-silica nanocomposite membranes./. Membr. Sd., 322 (2), 423 28. 

The solubility of a gas is an integral part for the prediction of the permeation properties. Various models for the prediction of the solubility of gases in elastomeric polymers have been evaluated (57). Only a few models have been found to be suitable for predictive calculations. For this reason, a new model has been developed. This model is based on the entropic free volume activity coefficient model in combination with Hildebrand solubility parameters, which is commonly used for the theory of regular solutions. It has been demonstrated that mostly good results are obtained. An exception... 

In the absense of any dependence of S and DT on penetrant concentration, the sorption and steady-state permeation properties of the membrane are described by effective solubility and permeability or diffusion coefficients given by... 

It is unknown how many subunits make up the pore of the PC2 channel. With an understanding of the permeation properties of the PC2 channel, an estimate... 

Figures 2.20 and 2.21 show the significant difference between diffusion in liquids and in rubbery and glassy polymers. A great deal of work has been performed over the last two decades to achieve a quantitative link between the structure of polymers and their permeation properties. No such quantitative structure-property relationship is at hand or even in sight. What has been achieved is a set of semiempirical rules that allow the permeation properties of related families of polymers to be correlated based on small changes in their chemical structures. The correlating tool most generally used is the polymer s fractional free volume v/ (cm3/cm3), usually defined as...

Correlation of the permeation properties of a wide variety of polymers with their free volume is not possible [32], But, within a single class of materials, there is a correlation between the free volume of polymers and gas diffusion coefficients an example is shown in Figure 2.24 [33], The relationship between the free volume and the sorption and diffusion coefficients of gases in polymers, particularly glassy polymers, has been an area of a great deal of experimental and theoretical work. The subject has recently been reviewed in detail by Petropoulos [34] and by Paul and co-workers [35,36],... 

The theory of permeation through microporous membranes in ultrafiltration and microfiltration is much less developed and it is difficult to see a clear path forward. Permeation through these membranes is affected by a variety of hard-to-compute effects and is also very much a function of membrane structure and composition. Measurements of permeation through ideal uniform-pore-diameter membranes made by the nucleation track method are in good agreement with theory. Unfortunately, industrially useful membranes have nonuniform tortuous pores and are often anisotropic as well. Current theories cannot predict the permeation properties of these membranes. 

N. Tanihara, H. Shimazaki, Y. Hirayama, N. Nakanishi, T. Yoshinaga and Y. Kusuki, Gas Permeation Properties of Asymmetric Carbon Hollow Fiber Membranes Prepared from Asymmetric Polymer Hollow Fibers, 7. Membr. Sci. 160, 179 (1999). 

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