Synergistic Effect of Stress and Nanoparticle in a polymeric Foam

Effect of screw speed and size of nanosilica on the foam structure was studied in a batch and an extrusion foaming system. Polystyrene, supercritical nitrogen and nanosilica was used as a matrix, blowing agent and nucleating centers, respectively. It was found that cell size decreases and cell density increases with decreases size of nanoparticles from 40 to 12 nm. Reducing size of nanosilica from 40 to 12 nm, increases available surface area of nanoparticles and enhances heterogeneous nucleation. However, decrement of nanoparticle size results in more enhancement in cell density and reduction in cell size of the produced foams. At the presence of shear stress, cell nucleation increases. The breakage of big bubbles to several smaller bubbles is the main reason for this result.