Permeability, Permeation nanocomposite

Relative oxygen permeability of nanocomposites with imidazolium modified montmorillonite as a function of filler volume fraction. The permeation behavior is compared with composites containing dioctadecyldimethylammo-nium ions [22] ( ) Ammonium and (a) Imidazolium composites. The dotted lines only serve as guides. (Reproduced from Mittal, V., Eur. Polym. /., 43, 3727, 2007. With permission from Elsevier.)... 

Clay nanocomposites are also being developed as barrier coatings for film and for containers. The nanocomposite is deposited on the film from a solution of PVOH/ EVOH copolymer in a mix of water and isopropyl alcohol which has been used in a supersonic dispersion system to nano-disperse 7 nm diameter silica and titanium dioxide particles. The ratio of polymer to silica depends on the barrier properties required. Typical microgravure equipment can be used to coat the solution onto a plastic substrate. The result reportedly is a transparent barrier coating which is superior to silica- and alumina-coated films, and is comparable to aluminum-coated materials. Oxygen permeability at a coating thickness of 2 pm is less than 1 cc/m d atm, and moisture permeation less than f g/m d. Costs are reported to be competitive with ceramic coatings [4]. 

Solubility increase mechanism depends on the interaction between the penetrants and nanofillers. The functional groups of nanofillers such as hydroxyl when occur on the surface of the inorganic nanofiller phase in rubber composites may interact with polar gases such as SO2. This condition can increase the penetrant solubility in the nanocomposite rubbers and, in turn, increase the gas permeability. The solubility increase mechanism model due to permeation coefficient parameter of gas, P is described using the Arrhenius equation ... 

Slavutsky et al. (2014) prepared starch/cellulose nanocrystals (CNCs) films and their water barrier properties were studied. The measured film solubility, contact angle, and water sorption isotherm indicated that reinforced starch/CNC films have a lower affinity to water molecules than starch films. Permeability, dififusivity, and solubility coefficients indicated that the permeation process was controlled by the water diffusion and was dependent on the tortuous pathway formed by CNC incorporation. The decrease in surface hydrophilicity and the improvement in water vapor barrier properties with the addition of CNC showed that these nanocomposites present excellent potential as a new biomaterial for application in food packaging and conservation. 

Fig. 8.6 Gas transport properties of CNT nanocomposite membrane. Gas transport properties of CNT/PS/PDMS membrane (triangle). CNTs/PS membranes (square), and Knudsen diffusion model (solid line), (a) Effeet of the pressure drop on the permeance of helium through CNTs/PS membrane, (b) Single-gas permeability as a funetion of the inverse square root of the molecular weight of the penetrant, (c) Single gas seleetivity with respect to He calculated from singe-gas permeability data, (d) Mixed-gas selectivity (CO /CH ) of CNTs/PS membrane. The composition of gas mixture was COjiCH =1 1. The feed pressure was 50 psi, and the pressure differential across the membrane was maintained by drawing a vaeuum on the permeate side. Operating temperature was maintained at 308 K. (From [8])...

The overall permeability of the sandwich film with plain PMMA facings and a PMMA—GO nanocomposite core was estimated using Eqn (8.15) considering the arrangement of three layers resisting the permeation of fluid in series. The theoretical values of permeability of the sandwich films based on the nanocomposite permeability values given in Table 8.22 were calculated and are presented in Table 8.23. 

Nylon 6-day nanocomposites of various day minerals with different cation exchange capadty (CEC) were prepared by in situ polymerization method, and properties such as mechanical, thermal, and gas permeability were compared with respect to pure nylon 6 (N6) polymer by Tsai et al. [35]. It is shown that the nature of the permeation of carbon dioxide gas depends on the exfoliation or intercalation of clay platelets. It is seen that the exfoliated clay platelets offer effective low permeability than the intercalated platelets as seen in Figure 8.2. 

Various models for composite permeability as they relate to nanocomposites have been reviewed and different models have been proposed [41—44]. The simplest way to model any composite property is to use a rule of mixtures approach. Polymer nanocomposite properties, however, do not generally follow this rule. Instead, fillers with high aspect ratio particles will influence the permeability of gases through the matrix more than filler particles with lower aspect ratios. Alignment/orientation of the filler particles (with respect to the axis of gas permeation) also plays a significant role in bulk permeability. Five models are briefly described in Sections 8.5.1-8.5.5. Predictions from these models are later compared to experimental mass loss rates. 

PTMSP, which has long been known as the most gas-permeable polymer, is still being investigated with respect to various aspects of its permeation of gases and liquids. The research subjects include the following membranes based on PTMSP for liquid-liquid separation the effect of direct-current discharge treatment on the surface properties of a PTMSP membrane cross-linking and stabilization of nanoparticle-filled PTMSP nanocomposite membranes for gas... 

Presently, PLA and other biopolyesters suffer from two important deficiencies that limit their use, of which the first is the low heat distortion temperature. The second is their relatively high permeabilities toward a number of substances, pmticularly water. Recently, copolymerization of cellulose acetate with PLA, both originating from renewable resources, resulted in a material with increased heat distortion temperature (200). In addition, nanocomposite technologies hold promise for improving both temperature distortion and permeation characteristics, as they have in conventional plastics. 

One of the main advantages of the nanostructured polymer blends is their enhanced barrier properties compared with pure polymeric matrix. The impermeable clay layers force a tortuous pathway for a permeate transverse the nanocomposites. The presence of nanoparticles is believed to greatly reduce the permeability of the pure polymer [40]. It was reported that the gas permeability through the polymer films can be reduced with small loadings of nanoclays [41]. 

The mass transport mechaiusm of gases permeating in a nanocomposite is similar to that in a semicrystalline polymer. The nanocomposite is considered to consist of a permeable phase where non-permeable nanoplatelets are dispersed. There are mainly three factors that influence the permeabiUty of nanocomposites the volume fraction of the nanoparticles, their relative orientation to the diffusion direction and their aspect ratio. The gas transport behavior of two different nanoclay-reinforced EVA membranes has been analyzed using oxygen and nitrogen gases and the results were compared with neat EVA. EVA nanostructured polymer blends exhibit excellent barrier properties. 

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