Vapor polymer blend permeability

Polymer blending has been established as an effective means for building up new properties gradually altering transport properties of polymeric materials. Examples include blends of nylon and polyethylene that exhibit combined permeability to water vapor and oxygen, which in some cases is lower than the permeability to either component. 

There are several kinds of polymer blends in use relating to gas permeability. One of the simplest involves films with different polymer layers, with each layer having a low permeability to a particular gas. Again referring to food preservation, one generally wants to keep oxygen out and water vapor in, for... 

The addition of PEOX to PES causes the water vapor diffusion coefficient to decrease in absolute magnitude, but to increase more strongly with activity. This behavior reflects the increased water sorption and the resultant tendency for materials containing PEOX to be plasticized, and overshadows the effect of the decrease in the free volume of dry polymer. The permeability coefficients for blends containing 10% and 20% PEOX were lower than those for PES, because the decrease in the diffusion coefficient was larger than the increase in the equilibrium water solubility. 

Polymer/sihca composite blends, not only improve the physical properties, snch as the mechanical properties and thermal properties of the materials, but they can also exhibit some unique properties that have attracted strong interest in many industries. Besides common plastics and rubber reinforcanent, many other potential and practical applications of this type of nanocomposites have been reported coatings, flame-retardant materials, optical devices, electronics and optical packaging materials, photo resist materials, photo-luminescent conducting film, per-vaporation membrane, ultra-permeable reverse-selective membranes, proton exchange membranes, grouting materials, sensors and materials for metal uptake, etc. As for the colloidal polymer/sihca nanocomposites with various morphologies, they usually exhibit enhanced, even novel, properties when compared with the traditional nanocomposites and have many potential applications in various areas. 

Plasticized polymers have been observed to behave like miscible blends. The permeabilities of oxygen, carbon dioxide, and water vapor in a vinybdene chloride copolymer increase exponentially with increasing plasticizer (4,5,28). About 1.6 parts plasticizer per hundred parts polymer is enough to double the permeablity. 

Wang X, Luo X, Wang X. Study on blends of thermoplastic polyurethane and aliphatic polyester morphology, rheology, and properties as moisture vapor permeable films. Polym Test 2005 24(1) 18-24. 

Ionic polymers with carboxylic and sulfonic acid functional groups have extremely high water permeabilities. Carboxy methyl cellulose/poly-acrylic acid blends show good water permeability and excellent selectivity for water over low alcohols (Table 1). These membranes can be effectively used to dehydrate alcohols [8]. Selectivity for water over alcohol increases with decreasing polarity of the alcohol. The water fluxes can be correlated with water vapor pressure and are not a function of the nature of the alcohol. 

Nontoxic Citrates Nontoxic citrate plasticizers derived from natural citric acid, such as triethyl citrate (TC), tributyl citrate (TBC), acetyl triethyl citrate (ATC), acetyl tributyl citrate (ATBC), and triacetine, have been shown to be effective plasticizers for PLA [27-29]. Some gas permeability tests have been performed to assess the potential use of PLA and nontoxic citrate plasticizer blends in food packaging and other applications. The effect of ATBC on PLA barrier properties was studied by Coltelli et al. [30] using PLA mixed with ATBC (10-35 wt%), followed by compression molding. Yu et al. [31] blended PLA/ATBC mixmres with carbon black (CB) to form electrically conductive polymer composites. Fourier transform infrared (FTIR) experiments revealed that the interaction between the PLA/ATBC matrix and the CB filler was increased by the addition of ATBC. Water vapor permeability values decreased with an increase in ATBC content (at constant CB levels). For example, at 30wt% CB, the WVP of the PLA decreased from 0.66 x 10 kgm/(msPa) (at 0% ATBC) to 0.10 X 10 kgm/(msPa) with the addition of 30% ATBC. 

The present study adds some insight into the interactions between two polymers but, more importantly, illustrates the type of property behavior that can be expected from miscible or immiscible - but compatible - blends which exhibit macroscopically uniform physical properties. The solubility, diffusivity and permeability behavior of numerous series of blends have been evaluated between 1974 and 2012. Whether or not a single phase exists depends on the chemical structure, molar mass distribution, and molecular architecture of the components present. Water, organic solvents and gases have been used as probes in sorption experiments and transport processes incorporating pervaporation, vapor, and gas permeation. 

Wang, X., X. Luo, and X. Wang, Study on Blends of Thermoplastic Polyurethane and Aliphatic Polyester Morphology, Rheology, and Properties as Moisture Vapor Permeable Films, Polymer Testing, 24(1), 18-24, 2005. 

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