Control of Foam Structure in PolyStyrene-Nanosilica-Carbon Dioxide: Effect of Temperature and Nanoparticles

This study addresses the effect of temperature and nanoparticle on PS foam structure in order to control its structure more accurately. For this purpose, a theoretical hypothesis was proposed by explaining the classical nucleation theory. The PS in the presence of nanosilica and CO2 was foamed. Foaming process was carried out in a vessel suitable under high pressure and temperature conditions, and with instantaneous pressure release and high-speed stabilization capabilities. The most important factors affecting foam properties including foaming temperature, size, content and surface properties of nanosilica were investigated. Increasing of foaming temperature was effective on the initial nuclei formation and cell growth. These two effects determined the final foam structure. When the temperature was changed from 90 to 180°C, cell density of PS foam increased thousand fold to 2.2×1012 number of cells per unit volume of foam (cell/cm3). The results showed that a small amount of nanosilica had a substantial effect on decreasing the cell size and increasing the cell density. An increase in nanoparticle concentration also increased its effectiveness. Moreover, the quality and structure of foam were improved by adding the nanoparticle. As the size of nanosilica increased from 20 to 40 nm, its cell density decreased from 3.3×109 to 1.78×109 numbers of cells per unit volume of foam (cells/cm3). Surface treatment of the nanosilica using triethoxysilane, in addition to improving nanoparticle dispersion, increased its cell density. The efficiency of nanosilica in improving cell density after surface treatment increased by more than double.