Microstructure characterisation of nanocomposite polymeric foams by X-ray microtomography

Recent advances in microstructured materials have given rise to many new types of composites that exhibit original and interesting physical properties. For example, a nanocomposite made of carbon nanotubes inside a polymer matrix shows exceptional electromagnetic interference shielding effectiveness when foamed. However, the effective properties of such materials strongly depend on the shape and topology of the microstructural cells. An accurate method for investigating the cellular microstructure is X-ray microtomography (XRµT), for it is non-destructive, and it provides 3D geometric information. Although it cannot be used to observe nanofiller dispersion, it has a strong potential for cell structure characterization.

In order to reduce the need for trial and error for tailoring these materials, our objective is to characterize, using XRµT, two different types of foaming procedures, namely supercritical CO2 batch foaming and freeze drying. As the resolution is limited compared to cell size, we have developed a novel statistical method based on 3D autocorrelation to determine characteristic length and examine anisotropy. We present results for these two types of foams and show the limitations of this method.