A microcellular foam was prepared from a thermoplastic elastomer by a batch physical foaming with CO2. Two hydrogenated polystyrene‐b‐polybutadiene‐b‐polystyrene (SEBS) copolymers with different styrene ratios were used as an elastomer basis and blended with polystyrene (PS) to control their rigidity and gas permeability. The end‐blocks of the SEBS form a physical cross‐link and provide a rubber‐like elasticity when cooled. SEBS alone, with its lower styrene content, cannot be physically foamed while retaining a stable‐shape dimension because of its higher gas permeability and lower rigidity. SEBS with higher styrene contents were used, or the PS blend ratio was increased to 80/20 or 50/50, and batch physical foaming experiments were conducted at three temperature levels (60, 100, and 120°C) while the sorption CO2 pressure was maintained at 10 MPa. Increasing the styrene content or blending PS with SEBS increased the storage modulus and decreased the gas permeability. As a result, the shrinkage of the foam was controlled, and stable microcellular elastomer foams could be prepared. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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 lm 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.

The effect of CO2‐induced crystallization on the mechanical properties, in particular the yield and the ultimate stresses, of polyolefins is studied. PP and SEBS copolymer blends are used as examples and foamed after sorption of CO2 at temperatures below Tm. CO2 sorption thickens the crystalline lamellae and consequently increases Tm from 160 to 178 °C for both pure PP and PP/SEBS blend systems. Foams with an average cell size smaller than 250 nm retain the ultimate stress at the level of the polymer before foaming, even without the effect of CO2‐induced crystallization. Including CO2‐induced crystallization, the yield and the ultimate stresses of the foam can be improved by 30 and 50% over solid PP and by 22 and 40%, for solid PP/SEBS blends, respectively.

The aim of this work is to study controllability of cell structure of foam by a Polypropylene (PP)/Polystyrene (PS)/ Polymethyl methacrylate (PMMA) ternary polymer blend. The effects of different polymer matrix, its blend morphology, and rheology on the cell structure of the ternary blend foam were investigated. The batch pressure quenched foaming of the ternary blend with supercritical carbon dioxide (CO2) was conducted in the temperature range from 60 to 160°C for PP matrix and 60 to 140°C for PS and PMMA matrices to observe the controllability of bubble location and size. The experimental results showed that interfacial tension, foaming temperature, and viscoelasticity are the important factors to control the cellular structure in ternary blend system.

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