High-barrier polymers

There are very few reports in the literature documenting the improvement in gas barrier properties that can be achieved using commercially available platelet-type fillers in melt processed polymer films and none showing the improvement in that class of polymers previously identified as high barrier polymers. 

High barrier polymers, such as polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polyester, acid copolymers and ionomers have been proposed and are under evaluation as a replacement for PE. However, they present some drawbacks in terms of scalability and/or mechanical properties and/or outgassing rates. Cost of these polymers is also generally higher. 

Adapted from Ref. 40. (According to these authors, high-barrier polymers have an oxygen transmission of not more than about 10 cc per mil of polymer per 100 in. of surface per day per 760 mm of mercury driving force at 23°C and humidity eonditions of use.)... 

More information on P, S, and D of water vapor of PLA and some conventional petroleum-based polymers at 23°C is summarized in Table 12.5. Table 12.6 provides data for water vapor permeance and permeability at 25 and 38°C. PLA has lower water vapor barrier properties than equivalent petroleum-based polymers, and it can be included in the group of low-barrier polymers following the classification of Salame and Steingiser [40]. In this classification, a high-barrier polymer has a water vapor permeation of not more than... 

Barrier properties of materials indicate their resistance to diffusion and sorption of molecules. A good barrier polymer has low values of both diffusion (D) and solubUity (S) coefficients. Since the permeabUity coefficient P is a derived function of D and S, a high-barrier polymer has low values of P. The diffusion coefficient is a measure of how fast a penetrant will move within the polymer in a particular direction, while the solubility coefficient gives the amount of the penetrant taken (or sorbed) per unit mass of polymer from a contacting phase per unit of sorbate concentration. Both diffusion and solubility can be applied to the reverse process of sorption, that is, the migration of compounds from the polymer to a surrounding media. Several factors influence the effective value of diffusion and solubility coefficients in polymers. 

Blending with high-barrier polymers is another approach to increase barrier properties of polymers like PET or polyolefins [40-42]. Yeo et al. [42] prepared a blend of polypropylene (PP)/ethylene-vinyl alcohol copolymer (EVOH) (85/15) using a single-screw extruder. Oxygen permeability of biaxially... 

Ozen I, Bozoklu G, Dalgicdir C, Yucel O, Unsal E, Cakmak M, Menceloglu YZ. Improvement in gas permeabUity of biax-iaUy stretched PET films blended with high barrier polymers The role of chemistry and processing conditions. Euro Polym J 2009 46 226-237. 

Some examples of high barrier polymers and their nanostructured blends are discussed in this section. 

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