Abstract
Polysulfone nanocomposite foams containing variable amounts of graphene nanoplatelets (0–10 wt%) were prepared by water vapor-induced phase separation (WVIPS) and supercritical CO2 (scCO2) dissolution. WVIPS foams with two ranges of relative densities were considered, namely, between 0.23 and 0.41 and between 0.34 and 0.46. Foams prepared by scCO2 dissolution (0.0–2.0 wt% GnP) were obtained with a relative density range between 0.35 and 0.45. Although the addition of GnP affected the cellular structure of all foams, they had a bigger influence in WVIPS foams. The storage modulus increased for all foams with increasing relative density and GnP’s concentration, except for WVIPS PSU-GnP foams, as they developed open/interconnected cellular structures during foaming. Comparatively, foams prepared by scCO2 dissolution showed higher specific storage moduli than similar WVIPS foams (same relative density and GnP content), explained by the microcellular structure of scCO2 foams. As a result of the plasticizing effect of CO2, PSU foams prepared by scCO2 showed lower glass transition temperatures than WVIPS foams, with the two series of these foams displaying decreasing values with incrementing the amount of GnP.
Highlights
Polysulfone (PSU) is an aromatic amorphous high-performance thermoplastic with high glass transition temperature and thermal-oxidative resistance, high strength and toughness, known for its resistance against hydrolysis and inherent fire resistance [1,2]
PSU-graphene nanoplatelets (GnP) nanocomposite foams prepared by the water vapor-induced phase separation (WVIPS) process displayed higher cell sizes and lower cell nucleation densities with incrementing the amount of GnP when compared to foams prepared by supercritical CO2 (scCO2) dissolution
Cell size slightly decreased by adding GnP for foams prepared by scCO2 dissolution, which could be the result of a barrier effect of graphene nanoplatelets to CO2’s diffusion during foaming
Summary
Polysulfone (PSU) is an aromatic amorphous high-performance thermoplastic with high glass transition temperature and thermal-oxidative resistance, high strength and toughness, known for its resistance against hydrolysis and inherent fire resistance [1,2]. In terms of mechanical performance, the results indicate that the resulting foams displayed significantly higher specific storage moduli due to the combination of the high stiffness of the added graphene nanoplatelets, enhanced nanoplatelets’ distribution and dispersion throughout the matrix promoted by foaming, and finer cellular structure of the foams With this idea in mind, in this work, the preparation of PSU-GnP nanocomposite foams by means of WVIPS and scCO2 dissolution and the analysis of their viscoelastic behavior is presented. This second foaming method does not require melt-compounding of the material, as in the case of scCO2 dissolution foaming (necessity to melt-compound the nanocomposites in order to have the required foaming precursors for scCO2 dissolution), and enables to control in an easier way the density ( allowing to extend the final range of densities) and cellular structure of the resulting foams; and the study for the first time of the viscoelastic properties of such complex multiphase materials, critical in terms of defining the possibilities of the material for extended applications, analyzing how the foaming method, amount of GnP, and resulting relative density and cellular structure may affect the mechanical performance of the foams
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