Influence of polyethylene disperse domain on cell morphology of polystyrene-based blend foams

Abstract

To gain insight into the foamability of polystyrene-based polymer blends containing different types of polyethylene close to the experimental boundary conditions of temperature, batch pressure quench foaming experiments were conducted using CO₂ as a physical foaming agent. The blends were prepared by melt-mixing in a twin screw extruder and then physically foamed by depressurizing CO₂ from 10 MPa in an autoclave at various foaming temperatures in the range of 90–140℃. At low temperatures, where viscosity of polyethylene (PE) was lower than that of PS, microcellular foams with bubble sizes of approx. 100 µm in diameter were obtained, and the dispersed PE enhanced bubble nucleation. It was also found that the expandability of bubbles was correlated with complex viscosity PE. At the highest foaming temperature, where the viscosity of PE became lower than that of the matrix, the dispersed PE worked as a cell opening agent.