Polymer nanocomposites permeability

Several studies were realized on the gas barrier in different polyimide/clay nanocomposites.Chang et prepared poly(amic acid)/organoclay 

The best fit of the Nielsen model (Equation 11.3) to the experimental data for O2 and water gave apparent particle aspect ratios of 46 and 130, respectively. Chang et al. suggest that the clay retains a crystallographic regular layer 

6 Water vapour permeability of polyimide nanocomposites as a function of clay content. (A) Polyimide/dodecylamine-clay nanocomposites (from Chang etal ) (B) Polyimide/hexadecylamine-clay nanocomposites (from Chang et a1. ) (C) Polyimide (BATB-ODPA)-clay nanocomposite (from Yeh etal. ) (D) Non-coplanar soluble polyimide (NSPI)-clay nanocomposite (from Yu et a/. ) (E) Polyimide/hexadecylamine-clay nanocomposites (from Chang et a/. ). 

7 Permeability to oxygen as a function of the organoclay content in the polyimide nanocomposite. (A) Polyimide-dodecylamine-clay nanocomposites (from Khayankarn etal. ) (B) Polyimide (BATB-ODPA)-clay nanocomposite (from Yeh (C) Polyimide/dodecylamine-clay 

Adhesive nanocomposites of polyurethane and montmorillonite modified with different organic residues have been synthesized and their permeability to oxygen and water vapour has been measured by Osman et al. The oxygen transmission rate asymptotically decayed with increasing aluminosilicate volume fraction and a 30% reduction was achieved at 3 vol.%, when the elay 

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Maiti and Bhowmick [205] have established a good correlation between the aspect ratio of clay in fluoroelastomer/clay nanocomposites and the transport properties of solvent. For fluoroelastomer/clay nanocomposites, permeability decreases significantly with the addition of only 4 phr of the unmodified mont-morillonite clay (0.14 x 10 s cm2 s ) compared with that of neat polymer (2.29 x 10 8 cm2 s-1)-... 

Patel NP, Miller AC, and Spontak RJ. Highly C02-permeable and selective polymer nanocomposite membranes. Adv. Mater. 2003 15 729-733. 

It is generally accepted that thermal stability of polymer nanocomposites is higher than that of pristine polymers, and that this gain is explained by the presence of anisotropic clay layers hindering diffusion of volatile products through the nanocomposite material. It is important to note that the exfoliated nanocomposites, prepared and investigated in this work, had much lower gas permeability in comparison with that of pristine unfilled PE [12], Thus, the study of purely thermal degradation process of PE nanocomposite seemed to be of interest in terms of estimation of the nanoclay barrier effects on thermal stability of polyolefin/clay nanocomposites. 

Explain the improvement in the following properties, with suitable examples, for different vegetable oil-based polymer nanocomposites (i) tensile strength, (ii) gas permeability, (iii) thermostability and (iv) biodegradability. 

Polymer nanocomposites find their first application in car hoods, which are easily attacked by NO pollutants since they are exposed to the exterior environment. NO at standard atmosphere and pressure is 29.5% NO and 70.5% N O. Polyamide-6 is highly sensitive to such pollutants. The infusion of nano-clay platelets in the polyamide matrix in general decreases the diffusivity and permeability of the nanocomposites to atmospheric oxygen... 

The decrease in permeability and enhanced gas barrier property of clay-polymer nanocomposites makes them viable for packaging application. 

The main uses of montmorillonite stem from its characteristic expansion, and it is used to control viscosity or impart thixotropy to a variety of liquid polymers based on unsaturated polyesters, PVC plastisols, polysulfides, alkyds, etc. It has also been reported to control the melt rheology of thermoplastics and to reinforce polyamides. There has, over the last few years, been enormous industrial and research interest, with many papers and patents, published on montmorillonite, especially as an organoclay as the basis of polymer nanocomposites. Because of the delamination process described above plastic-organoclay nanocomposites have been reported to have very high rigidity, low permeability to fluids, and fire resistance. This subject is covered in more detail in Chapter 10. 

Recently, polymer nanocomposites based on clay minerals have attracted great interest from researchers, both in industry and in academia, because they often exhibit concurrent improvement in several properties of neat polymer. These improvements can include high moduli, increased strength and heat resistance, decreased gas permeability and flammability, and increased degradability of biodegradable polymers [7-12]. These materials have also been proven to be unique model systems to study the structure and dynamics of polymers in confined environments [20]. 

POLYMER NANOCOMPOSITES WITH VERY LOW PERMEABILITY AND HIGH RESISTANCE TO AGGRESSIVE ENVIRONMENTS... 

The results reported on the thermal and thermooxidative decomposition of layered silicate nanocomposites are rather contradictory and do not lead to unambiguous or consistent conclusions. The results vary from enhanced decomposition, to no significant influence, to a strong improvement depending on the source and system discussed. The influence on thermal decomposition differs strongly from nanocomposite to nanocomposite. What is more, often the product release is changed rather than the primary decomposition reactions. The diffusion of the products is hindered by the decreased permeability for nanocomposites 5 wt% layered silicate-polymer nanocomposites show a reduction in gas permeability of around 40 to 60%, even for small gas molecules such as nitrogen and... 

FIGURE 3 Tortuosity in the path travelled during permeability of water vapor and oxygen through the polymer micro composite and polymer nanocomposites. 

The capacitance change upon absorption in nanocomposites with the filler concentration lower than the percolation threshold is another opportunity to monitor the dielectric permeability change. The effect consists of the existence of the dielectric constant anomaly for the conductive filler concentrations just below the percolation threshold values. The anomaly is due to the giant cross capacitance of big clusters of nanoparticles formed close to the percolation threshold which are not yet in contact with each other (the effect is similar to other critical phenomena, e.g. the behavior of ferromagnetics close to the Curie temperature). The absorption of the gas molecules by the polymer matrix leads to a highly non-linear capacitance change. The use of such polymer-nanocomposite layers placed on the top of field effect transistors (ChemFETs) has been proposed [41], but not yet realized. 

Biopolymer-nanoclay hybrid plastics - Polymer nanocomposites are used as packaging materials. Application of nanocomposites in the biopolymer packaging industry (e.g. films and bottles) potentially yields materials with low water vapor permeability (WVP) accompanied by a high transparency of the... 

The limiting cases for permeability of gas through a polymer nanocomposite system are devised taking into account only the permeability value and volume fractions of matrix and filler (Shields, 2008). 

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