Barriers containing flakes

Mica flakes embedded in a polymer and properly oriented in a plane can provide a tortuous path to vapors and liquids, similarly to the natural composites shown in Figure 1.1. Barrier properties can be imparted in blow-molded containers, packaging films, and corrosion-resistant coatings not only by mica but also by other impermeable lamellar fillers, including glass flakes, talc, and nanoclays. In blown LDPE film, the addition of 10% mica was found to reduce the oxygen permeabihty from 4.16 to 3.03 Barrer [37]. Assuming an impermeable, fully oriented lamellar filler, Eq. (8.1), [38] maybe used to predict the composite permeability. Pc, perpendicularly to the filler plane as a function of the matrix permeability, P , filler volume fraction, V(, matrix volume fraction, V , and filler aspect ratio a... 

Rhim et al. [116] reported that the water vapor permeability of PLA/Cloisite 20A (organically modified montmorillonite) composite films decreased significantly with increasing Cloisite 20A content (1.8 x 10 kgm/(m sPa) for Opph (part clay per 100 parts PLA)) to approximately 0.5 X 10 " kgm/(m sPa) for 15pph. Cussler et al. [126] developed and verified theories predicting the properties of barrier membranes to O2, water, and other solutes. Membranes that contained impermeable flakes or lamellae showed much lower permeabilities than conventional membranes. The variation of permeability depended on the concentration and aspect ratio of the flakes. 

A variety of discontinuous (short) functional fillers may be combined with thermoplastic or thermoset matrices to produce composites. The fillers may differ in shape (fibers, platelets, flakes, spheres, or irregulars), aspect ratio, and size. When the fully dispersed (exfoliated or deagglomerated) fillers are of nanoscale dimensions, the materials are known as nanocomposites. They differ from conventional microcomposites in that they contain a significant number of interfaces available for interactions between the intermixed phases. As a result of their unique properties, nanocomposites have great potential for applications involving polymer property modification utilizing low filler concentrations for minimum weight increase examples include mechanical, electrical, optical, and barrier properties improvement and enhanced flame retardancy. 

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