The Effect of Surface Properties and Content of Nanosilica Particles on Polystyrene Foam

Nucleating agents are commonly used for controlling cell nucleation in the production of high-quality foam products. The surface properties of nanoparticles include geometrical characteristics, such as the particle shape, size, and size distribution and in this respect there are few reports on the effects of geometry of particles on foaming efficiency. This study is an effort to control polymeric foam structure with addition of silica nanoparticles in a batch process. In this research polystyrene (GPPS 1540) was used as a matrix, nanosilica as nucleating agent and supercritical carbon dioxide (CO2) as blowing agent. For better dispersion of nanoparticles in the matrix, a combination of solution and melt method was employed. In continuation, the effect of surface treatment of nanoparticle on polymer foam is investigated. First, silica nanoparticles were modified by reaction with vinyltriethoxysilane followed by characterization of the results. Then, the surface tension of polystyrene, silica and modified silica were determined by contact angle test in order to predict the dispersion of nanoparticles in polystyrene. Then, two kinds of polystyrene/silica (treated and non-treated) nanocomposites were prepared with different filler loadings by a combination of solution and melting methods. A high pressure/high-temperature vessel capable of instantaneous pressure release and controlled stabilization was used to prepare polystyrene-nanosilica nanocomposites foam. The effect of surface treatment of nanosilica particles on microcellular foaming was investigated by characterizing the cell density and cell size of the foamed product using SEM. The results showed that surface-treated nanosilica has considerable effect on decreasing cell size and increasing the cell density