Permeability nanocomposites

Tsou and Measmer examined the dispersion of organosUicates on two different butyl mbbers, namely BIMS and brominated poly(isobutylene-co-isoprene) (BIIR) with the help of small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), atomic force microscopy (AFM), and TEM [91]. There is also a patent on BIMS nanocomposites for low permeability and their uses in tire inner tubes [92]. 

As a result, the permeability of nanocomposites (Pf) is reduced from that of the neat polymer... 

FIG. 6 Relative permeability (PcIPo) vs volume fraction of clay for poly(e-caprolactone)-mont-morillonite nanocomposites. (From Ref. 57.)... 

In 2002, Lee et al. [51] reported the biodegradation of aliphatic polyester-based nanocomposites under compost. Figure 9.13(A, B) represent the clay content dependence of biodegradation of APES-based nanocomposites prepared with two different types of MMT clays. They assumed that the retardation of biodegradation was due to the improvement of the barrier properties of the aliphatic APSE after nanocomposite preparation with clay. However, there are no data about permeability. 

It is necessary to disperse the nanomaterials in the best possible manner, especially those layered structures such as graphite, graphene or clays. It is important to obtain very thin (ca. one nanometer) and very wide (ca. 500 nanometers) nanostructures dispersed in the polymer matrices to achieve optimal gas permeability and to improve their mechanical properties without affecting structural quality, using a small amount of the nanomaterial. The particle orientation also has an important effect on the properties of the nanocomposite. Nanoparticles need to be dispersed within the polymer so that are parallel to the material s surface. This condition ensures a maximum tor-... 

Thermal treatment of the nanocomposite film formed in Scheme 6 converts the amic acid groups of the film to imides (Eq. 15). In addition to evidence by IR spectroscopy, elhpsometry showed that the film thickness decreased by ca. 15% and contact angle goniometry showed that the film became more hydrophobic (see Table 2). This thermally treated film also did not have the pH dependent permeability of redox-active ions previously described for dendrimer/Gantrez films on gold substrates [55]. 

Fig. 10 pH-Dependent permeability of the anions Fe(CN)6 and the cation Ru(NH3)g in nanocomposite dendrimer-poly(maleic anhydride) grafts that contain - CO2H/ - C02" and NH2/-NH3 groups in the film with a anion permeability at low pH where the... 

Nanocomposites are being used in tires, in particular, tire inner liners. Here, less permeable inner layers are achieved by the introduction of clad layers, which allow the use of a thinner inner liner, resulting in an overall lighter tire. Tire inner layers are typically derived from butyl rubber, often halogenated butyl rubber. 

Fig. 32 Validation of different permeability models in the PU-based nanocomposite systems...

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. 

Another advantage of PCNs is the substantial decrease in permeability. The drastic decrease in permeability is attributed to the large aspect ratio of the clay layers, which increase the tortuous path of the gas as it diffuses into the nanocomposites. 

Technology for preparing nanocomposites directly via compounding has been investigated by Vaia, Ishii, and Giannelis. Industrial R D efforts have focused on process technology (e.g., melt or monomer exfoliation processes), as there are a number of polymers (e.g., polyolefins) that do not lend themselves to a monomer process. Nanocomposites with a variety of polymers, including polyacrylates or methacrylates, polystyrene, styrene-butadiene rubber, epoxy, polyester, and polyurethane, are amenable to the monomer process. The enhancement of mechanical properties, gas permeability resistance, and heat endurance are the primary objectives for the application of PCN, and their success will establish PCNs as a major commercial product. 

Figure 16.25. Water permeability of nanocomposite and polyamide composite conventionally filled with silicate. [Adapted, by permission, from Giannelis E ,Adv. Mat., 8, No.l, 1996, 29-35.]...

The methanol permeability of the nanocomposite membranes was shown to decrease on addition of the sulfonated titanate. Functionalized montmorillonite (MMT) was also employed to improve PFSA [58, 59] these composite membranes provide a low methanol crossover, without sacrifidng proton conductivity due to the introduction of sulfonic acid groups at the MMT surface, followed by blending with the Nafion ionomer. 

The analytical expressions of micromechanics are generally most accurate at low volume fractions of the filler phase. The details of the morphology become increasingly more important at higher volume fractions. This fact was illustrated by Bush [64] with boundary element simulations of the elastic properties of particulate-reinforced and whisker-reinforced composites. The volume fraction at which such details become more important decreases with increasing filler anisotropy, as was shown by Fredrickson and Bicerano [60] in the context of analytical models for the permeability of nanocomposites. 

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. 

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