Composite foams with anisotropic structural and functional properties

Composite lightweight materials based on a polymeric matrix with embedded magnetic microparticles were developed. The application of a magnetic field (MF) during the foaming of samples tailored the assembling of magnetic particles along the MF lines, forming reinforcing chain-like structures in the foamed polymer. The presence of aligned micro-particles imparted peculiar anisotropic structural and functional responses. In fact, such foams showed higher compressive performances (in terms of Young's modulus and compressive strength) along the alignment direction with respect to randomly reinforced foams. The proper variation of the processing parameters during foaming allowed to change the constitutive stress-strain compressive relationship. Samples with aligned particles exhibited improved performances with particle volume content, in accordance with the increase of linear aggregates length and thickness. On the contrary, the mechanical response of randomly dispersed particle foams was almost independent on the volume content. The effect of the the application of a MF after foaming was investigated. A magneto-elastic behaviour was showed by all systems but the presence of aligned particles strongly increased the mechanical response. A magnetostrictive or magnetostrengthning effects were exhibited in dependence of the compressive strain applied to foams with aligned particles.