Gas-permeability properties

There is a region of thin films with thicknesses between the two previously described extreme limits, ranging from 100nm to several micrometers, where volume relaxation processes - and, hence, the change in gas-permeability properties with time - are much more rapid than that expected based on observations of bulk specimens as shown below. 

The experimental results described above show that the gas-permeability properties of thin glassy polymer films (submicrometer in thickness) are more time- or history-dependent than much thicker films (the bulk state for example, 50 pm or thicker) seem to be. This is manifested in terms of physical aging over a period of 1 year and more. The observed permeability values for the current thin films are all initially greater than the reported bulk values but approach or become less than these values after a few days or weeks, depending on the thickness. After a year, the thin films may be as much as four times less permeable than the reported bulk values. Selectivity increases with aging time, as might be expected from a densification process. 

Other important characteristic of a porous hydride bed is its gas permeability -property of a porous material to pass through itself gas under action of the enclosed gradient of pressure. In conditions of viscosity mode of hydrogen flow in a porous bed the density of a stream of hydrogen is connected by linear dependence to a... 

Structure Level n effects on gas permeability properties of the polyimides discussed in this paper are especially Interesting when considered with regard to the role of solubility and diffusion parameters on permeability properties. From segmental shape considerations it is clear that the solubility and diffusion... 

Gas transport through polymers is an area of growing interest as materials with unique transport properties continue to find use in new, specialized applications ranging from extended life tennis balls (1) to natural gas separation systems (2.) Concurrent with this increased interest is the desire to understand on a molecular level what determines the gas permeability properties of a particular material. The ability to better relate polymer molecular structure to gas transport properties is crucial in any attempt to rationally design materials for specific permeability applications such as gas barriers. 

This phase has presumably mobility and therefore gas permeability properties differing from fhe bulk. Based on fhis consideration, the oxygen permeation through the confined polymer phase was tentatively assumed to be negligible with respect to the bulk one, and a modified version of the tortuous path model of Gusev and Lusti taking into account the total non permeable volume (silica plus volume of confined polymer chains) was derived (Figure 11.27). 

Vassiliou, A., Bikiaris, D., and Pavlidou, E. (2007) Optimizing melt-processing conditions for the preparation of iPP/ fumed silica nanocomposites morphology, mechanical and gas permeability properties. Macromol. React. Eng., 1 (4), 488-501. 

Reid B D, Ruiz-Trevino F A, Musselman I H, Balkus Jr K J, Ferrari P (2001) Gas Permeability Properties of Polysulfone Membranes Containing the Mesoporous Molecular Sieve MCM-41. Chemistry of materials 13 2366-2373. 

In parallel, it has also been formd that mechanical properties, flexural properties, heat distortion temperature, and oxygen gas permeability properties can be greatly improved by modifying PLA with organically modified layered silicate (OMLS) nanocomposites [36]. This is the basis of new PLA manufacture developed by Toyota. 

Polysaccharide-derived films exhibit excellent gas permeability properties, resulting in desirable modified atmospheres that enhance the shelf life of the product without creating anaerobic conditions (Baldwin, Nisperos, Baker, 1995). 

In this paper, physical aging of gas permeability properties of PTMSP is described using the dud mode sorption and transport model, lliis model is also used to rationalize the increase in stability of gas permeation properties as a result of blending PTMSP with poly(tert-butyl acetylene) (PTBA). 

Many papers have been published regarding the gas permeation properties of polyimides(7-7). Polyimides are very useful polymers for the analysis of relations between gas permeation properties and polymer structure, because many different structures, based on diadds and diamines, can be prepared from existing compounds. We have previously reported relations between free volume or cohesive energy density and gas diffusivity(8,9). In this study, we prepared five kinds of polyimides and explored correlations between gas diffusivity and parameters such as stor e modulus, cohesive energy density, and free volume. These results were con iared with data from previous studies. We dso discuss the merits of the use of each of these parameters to correlate gas permeability properties of different polymers. 

The separation of gas mixtures by polymeric membranes has become a commercially important methodology for a number of different systems (1). Several recent review articles have discussed the interaction between polymer structure and gas permeability properties (2,3). The quantification of the effect of polymer structure on gas transport properties recently has been reported (4,5) and it is now possible to optimize gas transport properties for well defined polymeric materials. For those materials which do not have a well defined data base it is necessary to prepare and measure the gas transport properties. The polyamide-imides (PAI) are a class of polymeric materials which do not have an extensive data base for gas transport properties (6,7). Work by Yamazaki and coworkers (8) demonstrated that PAI materials could be prepared easily and in a manner whereby the amide bond could be prepared from a phosphite activated carboxylic acid and an aromatic amine. Yang and CO workers (9-11) have shown that novel dicarboxyl ic acids could be prepared from trimellitic acid anhydride (TMA) and aromatic diamines and that these dicarboxylic acids could be coupled with a second diamine to form regiospecific PAI materials. Our focus was to examine the effects of a phenylene diamine and its alkylated analogs on the gas transport properties of regiospecific PAI materials and to identify those structures which maximized both permeability and selectivity. 

Figure 3.3 Diagram of film structure used by Rowe et al., which enabled the study of gas permeability properties and physical aging behavior of ultra-thin glassy films. Reproduced with permission of Elsevier. ...

Pinto AM, Cabral J, Tanaka DAP, Mendes AM, Magalhaes ED (2013) Effect of incorporation of graphene oxide and graphene nanoplatelets on mechanical and gas permeability properties of poly (lactic acid) films. Polym Int 62(l) 33-40... 

Ethylene ionomers, such as Surlyn from DuPont , have been the premium sealant materials for packaging applications due to their excellent seal strength and process robustness. The ethylene ionomers achieve the unique property characteristics through the development of a network morphology. In this paper the development of new ethylene ionomers will be discussed. The versatile compositions and the unique morphology of the new ionomers will be presented together with the novel gas permeability properties. Their enhanced breathability to oxygen, carbon dioxide, moisture, etc., selective permeability, and smart barrier properties will be presented. 

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