Hybrid polymers, barrier properties

TABLE 21 -5. SUMMARY OF IMPORTANT REFERENCE DATA AND PROPERTIES OF NEW HYBRID POLYMER BARRIER COATING MATERIALS (FOR SEE FIG. 21-11)... 

Polymer-clay nanocomposites (PCN) are a class of hybrid materials composed of organic polymer matrices and organophilic clay fillers, introduced in late 1980s by the researchers of Toyota (Kawasumi, 2004). They observed an increase in mechanical and thermal properties of nylons with the addition of a small amount of nano-sized clays. This new and emerging class of pol miers has found several applications in the food and non-food sectors, such as in constmction, automobiles, aerospace, military, electronics, food packaging and coatings, because of its superior mechanical strength, heat and flame resistance and improved barrier properties (Ray et al., 2006). 

Park, H.W., Lee, W. K.,Park, C. Y.,Cho, W. J., Ha, C. S. (2003). Environmentally friendly polymer hybrids Parti. Meehanical, thermal, and barrier properties of thermoplastie stareh/elay nanocomposites. Journal of Materials Science, 38, 909-915. 

PAR 03] Park H.M., Lee W.K., Park C.Y., et al, Environmentally friendly polymer hybrids Part 1 mechanical, thermal, and barrier properties of thermoplastic starch/clay... 

The incorporation of nanoclays and natural fibres in resin systems thus provides reinforcements to resin systems at two scales. The nanoclay enhances the bio-based polymer system in stiffiiess and hygrothermal properties, while the natural fibres provide the main stiffness and strength. In addition, the enhanced barrier properties of the nano-reinforced resin retard moisture from reaching the natural fibres and thereby providing a synergetic effect between scales for an efficient bio-based composite. Hybrid bio-based composites that exploit the synergy between natural fibres (industrial hemp) in a nano-reinforced bio-based polymer can lead to... 

The decrease in weight gain for the nanophased composites can be attributed to the hybrid exfoliated and intercalated nanoclay platelets in polymer. Nanoclay platelets when exfoliated/dispersed well in the matrix provide the barrier to gas/liquid in a tortuous manner [12]. This can be attributed to the gas/moisture and radiation barrier properties of montmorillonite nanoclay, which is consistent with results reported by Woo et al. [35]. 

Polymer/mbber nanocomposites exhibit enhanced mechanical, thermal stability, toughness, stiffness, and gas-barrier properties compared to those of conventional composites at same filler volume fraction [11-15]. The interaction between the filler and polymer matrix of nanocomposites at the nanometer scale enables the formation of molecular bridges in the polymer matrix. This is the basis for the enhanced mechanical properties of nanocomposite as compared to conventional microcomposites [16, 17]. Nanocomposites containing hybrid fillers add a new dimension to the above enhanced properties. These composites show more advantages to composites containing single filler as the property of the hybrid filler composite depends upon the combined effect of individual filler. The nonlinear viscoelastic behavior of nanocomposites can be influenced differently by hybrid fillers than single filler. 

In order to obtain hydrophobic materials, fluorosilanes in quantities of < 1 mol% were added to the coating sols (see Fig. 21-11, compounds 9,10). This has a favorable effect on the barrier properties to polar permeants such as water vapor (PES/SiO /hybrid polymer WVTR 0.18 g/m d PES/SiO /hydrophobic hybrid polymer WVTR 0.03 g/m d, layer thickness in both cases 4 fim). 

The above comparison with the commercial packaging film puts in perspective the very promising results for the hybrid polymer (see Fig. 21-15(B), BOPP metallized) in improving the barrier properties against flavor permeation. 

Water Vapor and Oxygen Barrier Properties. The measurements of the water vapor and oxygen permeation were carried out on various polymer films (with and without vapor-deposited layers) and on multilayer laminates ([PET/SiO ]2hybrid polymer). Figure21-18 shows a scanning transmission micrograph of a laminate consisting of PET/SiOj /hybrid polymer. 

The most remarkable features of the hybrid polymer based structures are their excellent adhesion and barrier properties even after being subjected to high mechanical and thermal loads and after storage under humid conditions (see Table 21-2). 

Thirdly, experiments have shown that the application of an initial hybrid polymer coating, acting as a planarizing layer (see Fig. 21-22(c)), has a positive influence on the barrier properties of the overall PET/MeOj laminate (see Table 21-4). 

TABLE 21 -4. OTRs OF PET FILMS COATED WITH HYBRID POLYMER AND AIO (BIF BARRIER PROPERTIES OF THE UNCOATED SUBSTRATE RELATIVE TO THE COATED SUBSTRATE)... 

As can be seen from Figure 21-28, the barrier values for apphcations involving VIPs, LFDs and solar modules are aheady met. In order to achieve the required water vapor barrier properties for OLFDs, further work is stih required. In order to break through into areas where such low permeabilities are required, it is not only the barrier properties of the hybrid polymers that matter, but also harmonization and optimization of ah processes, materials and methods that are used for producing the multilayer laminates. 

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