Polypropylene-Dispersed Domain as Potential Nucleating Agent in PS and PMMA Solid-State Foaming

The potential of using dispersive domains in a polymer blend as a bubble nucleating agent was investigated by exploiting its high dispersibility in a matrix polymer in the molten state and its immiscibility in the solid state. In this experiments, polypropylene (PP) was used as the nucleating agent in polystyrene (PS) and poly(methyl methacrylate) (PMMA) foams at the weight fraction of 10, 20, and 30 wt %. PP creates highly dispersed domains in PS and PMMA matrices during the extrusion processing. The high diffusivity of the physical foaming agent, i.e., CO(2) in PP, and the high interfacial tension of PP with PS and PMMA could be beneficial for providing preferential bubble nucleation sites. The experimental results of the pressure quench solid-state foaming of PS/PP and PMMA/PP blends verified that the dispersed PP could successfully increase the cell density over 10(6) cells/cm(3) for PS/PP and 10(7) cells/cm(3) for PMMA/PP blend and reduce the cell size to 24 mu m for PS/PP and 9 lm for PMMA/PP blends foams. The higher interfacial tension between PP and the matrix polymer created a unique cell morphology where dispersed PP particles were trapped inside cells in the foam. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 1042-1051, 2011