Heterogeneous Nucleation in Batch Foaming of Polystyrene in Presence of Nanosilica as a Nucleating Agent

Atheoretical hypothesis was put forward on the effect of nanoparticle size on cell nucleation in polystyrene (PS) matrix foam. At first the heterogeneous factor was calculated in different wetting angles from zero to 180º. Then، to verify this hypothesis a combination of the solution and melting methods was used to prepare PS-nanosilica nanocomposites at different concentrations and different sizes of nanosilica. In this regard a novel apparatus، including a high-pressure/ high-temperature vessel capable of instantaneous pressure release and stabilization control، was used to prepare a polystyrene-nanosilica nanocomposite foam in its melt state. To reach the foaming conditions، the vessel was pressurized with dry ice at the specified temperature. After reaching the foaming conditions، the sample was saturated with supercritical carbon dioxide (CO2) for 8 more hours. Then، the pressure was released with an on/off valve and the temperature was instantaneously dropped to below glass transition temperature. The scanning electron microscopy pictures were used to calculate the effect of nanosilica on the main foaming parameters including cell density and cell size. The results showed that a small amount of nanosilica has substantial effect on decreasing cell size and increasing the cell density. Moreover، the foam quality and structure was improved by addition of the nanoparticle.