Barrier properties of a nanocomposite comprised of perfectly aligned randomly dispersed platelets are described in this communication. The finite‐element based methodology employed is generic and can readily be used to identify the role of various morphological imperfections typical of nanocomposites. The Figure shows a sketch of a periodic multi‐inclusion computer model comprised of 25 identical parallel non‐overlapping identical platelets of aspect ratio 50.

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Summary: Organophilized montmorillonite‐epoxy and ‐polyurethane nanocomposites, useful for packaging applications, were prepared and their oxygen permeability was measured. The composite morphology was mixed, exfoliated and intercalated, as shown by wide‐angle X‐ray diffraction (WAXRD) and transmission electron microscopy (TEM). The gas‐barrier performance of the polyurethane composites was better than that of the epoxy composites due to more exfoliation. The average aspect ratio of the montmorillonite platelets in the nanocomposites could be estimated from the reduction in permeability by a numerical finite element approach.A computer model comprising 50 randomly distributed and oriented round platelets with an aspect ratio of 50 at 3 vol.‐% loading, periodic boundary conditions applied.imageA computer model comprising 50 randomly distributed and oriented round platelets with an aspect ratio of 50 at 3 vol.‐% loading, periodic boundary conditions applied.

It is fairly common in practice that during injection moulding, the mold filling process results in non‐uniform fiber orientation distributions in the final injection molded short fiber reinforced composite part. It would be very attractive to employ an orientation averaging scheme to form predictions for the design of short fiber reinforced composite parts. Here, the authors use a finite‐element‐based numerical procedure developed by themselves and, for the first time, directly predict the stiffness and thermal expansion of several hundred multi‐fiber computer models with a variety of different predefined fiber orientation states.

The overall effective thermoelastic properties of nanotube reinforced polymers (NRP) were estimated numerically by using a finite element based procedure. Three-dimensional multi-inclusion periodic computer models were built for three different nanotube orientation states, namely, fully aligned, two-dimensional random in-plane and three-dimensional random states. The enhancement of the Young's modulus as well as the decrease of the thermal expansion coefficient were calculated numerically, assuming technologically relevant combinations of the nanotube aspect ratio and volume fraction. Maximal changes of the thermoelastic properties can be achieved in the longitudinal direction of NRPs with fully aligned carbon nanotubes whereas two-dimensional random in-plane and three-dimensional random composite morphologies exhibit more moderate enhancements but in more than one direction. Numerical predictions for the enhancements of the thermoelastic properties confirmed that carbon nanotubes can be considerably more effective for the reinforcement of polymers than conventional glass or carbon fibres.