Emulsion-derived (PolyHIPE) foams for structural materials applications
The simplest type of sandwich composite consists of two, thin, stiff strong sheets of dense material separated by a thick layer of low density material. The first major structure to incorporate sandwich panels was the Second World War "Mosquito aircraft" which consisted of a balsa wood core with plywood faces. The cellular materials used for sandwich core applications can generally be divided into two categories; honeycomb structures and polymer foams. Other cellular cores which exist are balsa wood and corrugated cores. Honeycomb materials generally have a hexagonal cellular shape, and are the core material of choice for advanced composites, In this thesis it was the aim to prepare open-cellular PolyHIPE foam core materials by the polymerisation of the continuous phase of a high internal phase emulsion (HIRE). To assess whether PolyHIPE materials are viable as core materials their flexural, compressive and shear properties were evaluated against the current commercially used core materials. It was shown that it was possible to improve the flexural, compressive and shear properties of a styrene/DVB PolyHIPE material by the addition of fibres to the material and the use of an optimised surfactant system (OSS). It was also shown that by the addition of monomers such as; butyl acrylate, 2-ethylhexyl acrylate, butyl methacrylate and methyl methacrylate to the monomer phase that the compressive properties of the S/DVB material could be varied. It was also possible to prepare a fibre-free and fibre-reinforced resorcinol- formaldehyde-based material, which had greater compressive and shear properties compared to the styrene/DVB material. Also a PolyHIPE material containing poly (ϵ-caprolactone) diacrylate showed shape-memory properties and an elongated cell structure after deformation and cooling. This elongated cell structure could lead to possible anisotropic behaviour. Finally it was concluded that the best mechanically performing PolyHIPE materials prepared competed well with the shear and compressive strength of the commercial honeycomb and foam core materials examined.