Nanofiller reinforcing agents can significantly improve the strength and modulus of polymer foams. But these improvements are often accompanied by changes in foam density (or equivalently the expansion ratio or void volume). The efficacy of nanofillers as reinforcing agents can only be judged once the density differences are accounted for. We review the literature and show that representing the data on Ashby charts of modulus against foam density is an effective way of evaluating whether nanofillers have a significant reinforcing effect or not. The literature suggests that strength and improvements due to nanofiller -after accounting for foam density changes -are typically modest for thermoplastic foams. However, major improvements are possible for reactively generated foams, especially flexible polyurethane foams.

The coexistence curves of the liquid-liquid equilibria (LLE) for systems of dimethylformamide (DMF) with hexane, heptane, octane, or nonane and of dimethylacetamide (DMA) with heptane have been determined visually. All the curves show an upper critical solution temperature (UCST) and have a rather horizontal top. The measured LLE curves for DMF mixtures show that their symmetry depends on the size of the alkane. For a given alkane, the UCST is higher for systems with DMF. This reveals that dipole-dipole interactions between amide molecules are stronger in such solutions. The DISQUAC model represents fairly well the LLE curves.

This paper presents the production method and the compressive mechanical response at low strains for a collection of polyethylene foams with high densities and cell sizes in the microcellular range. The materials were produced using a modified compression moulding technique that allows and independent control of density and cell size. The materials had a relative density between 0.27 and 0.92, an homogeneous and multistructured cellular structure with dense skin and foamed core and cell sizes in the range 30 to 100 microns. The Young´s modulus was reduced when density did. For relative densities higher than 0.7, the reduced Young's modulus of the foams was higher than that of the solid. In addition, it has been proved that variations in the cell size at constant density did not influence the Young's modulus. The advantages of using these materials for the production of plastic pipes have been analysed. A reduction of the weight of pipes loaded in compression of up to 42 % can be reached by using these foams in spite of the solid material from which the foam was produced.

This article presents the compressive mechanical response at low strains for a collection of polyethylene foams with high densities and cell sizes in the microcellular range. The materials under study had a relative density between 0.27 and 0.92, a homogeneous and multi-structured cellular structure with a dense skin and a foamed core. The Young's modulus and collapse stress were reduced when density did, the modulus following a linear trend and the collapse stress a quadratic tendency. For relative densities higher than 0.7, the materials showed Young's modulus slightly above the limit given by a potential law with exponent equal to one. In addition, it has been proved that variations in the cell size did not influence the elastic properties. The advantages of using these materials for flat structural panels have been analyzed. A reduction of the weight of flat panels loaded in bending of up to 35% can be reached by using these foams in spite of the solid sheet from which the foam was produced.

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