Barrier behavior

Figure 6.4 Reaction coordinate diagrams showing various types of energy-barrier behavior...

The chemical structure of the polymer s constitutional unit is the fundamental determinant of the polymer s barrier behavior. In addition to chemical composition, polarity, stiffness of the polymer chain, bulkiness of side and backbone-chain groups, and degree of crystallinity significantly impact the sorption and diffusion of penetrants, and hence permeability. Of particular significance are influences on the free volume and molecular mobility of the polymer, and influences on the affinity between the permeant and the polymer. 

Gas and water-permeability PLA has insufficient barrier behavior to oxygen, carbon dioxide, and water vapor compared to other benchmark packaging polymers such as polyolefins (PE, PP) and PET [19]. 

Two main problems discussed above have to be overcome in order to achieve high 7c values. The first one is the current barrier behavior of the grain boundaries, which can be solved by texturing of the crystalline... 

Polyhydroxyalkanoates and polyhydroxybutyrate in particular may be considered as rather controversial polymers. PHB is sometimes referred to as a material that appeared too early, before its time has came. To summarize, PHAs are prepared from renewable resources and are fully biodegradable. They outperform most of the other biodegradable polymers and many synthetic plastics in properties, notably mechanical strength and modulus, resistance to water and moisture due to high hydrophobicity, high crystallinity and several other physical properties such as barrier behavior or piezoelectricity. 

A field of growing attention is the development of polymer-clay nanocomposites due to the significant technological applications of these materials. Therefore, composite systems produced by organic polymers and clay minerals prepared at the nanoscale level, which typically present a unique layered structure, rich intercalation chemistry and availability at low cost, have been used to develop plastic materials with superior mechanical properties, molecular barrier behavior, fire retardant abilities, enhanced thermal stability, among other properties, compared to the individual polymeric materials [3-5]. 

The unique smart vapor barrier behavior of FAMTs, when applied in a house or roof liner application, enables the liners to respond to the seasonal weather changes and effectively dissipate the moisture to prevent the water condensation induced mold growth. 

Mount III, Eldridge, M., Wagner, John R., Aroma, Oxygen and Moisture Barrier Behavior of Coated and Vacuum Coated OPP Films for Packaging , /. Plastic Film Sheeting, V17(July), 2001, pp 221-237. 

Simultaneous improvements of tensile strength, scratch resistance, storage and loss modulus, gas barrier behavior, thermal stability, and flame retardancy can be achieved for many common polymers by dispersing into them less than 5% of clay. ° These improvements are only observed and transparency of the material is only maintained if the individual silicate sheets of clay are nanodispersed, that is, if they form an intercalated or exfoliated stmcture (Figure 18). However, a majority of industrial polymers is unpolar and thus incompatible with the silicate sheets, which carry negative surface charges. Silica sheets do not disperse in such polymers unless the silica surface is modified by a surfactant. 

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