Microcellular technology is an advanced foaming technique which uses inert gas as a foaming agent and brings many merits such as improved impact strength and toughness. Microcellular foaming was developed as a batch process but unfortunately, the time required for foaming is too long. Extrusion and injection molding are under development so that microcellular foaming may be profitably used in industry. In our research, we designed a controllable ratio of flow length to cavity thickness L/t mold for microcellular foaming and measured volume expansion as a function of L/t. We obtained uniformly distributed microcells about 30μm in size and observed 30.1% volume expansion for L/t=20. Volume expansion data are necessary for designing a mold system that is proper for microcellular foam moldng.

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Recently, the development of high-performance thermoplastic polymer composites has been a focus for the polymer engineering field. These polymer composites are formulated with polymer blends and alloys and various fillers. Twin-screw extruders can provide excellent mixing for these composites. The filler dispersion depends on processing conditions such as processing temperature, residence time, screw speed and screw profile. The physical properties of these polymer composites are also strongly dominated by the dispersion conditions of the filler.
In this study, conductive carbon-nanotube (CCNT) was used as a filler and polycarbonate (PC) as the matrix polymer. The conductivity of these composites was measured and related to the dispersion of CCNT under different processing conditions. The dispersion was characterized by the dispersion ratio. The total shear strain [γ·t], the product of shear rate [γ] and residence time distribution [t], was used as a dispersion parameter.
We can conclude that the filler dispersion depends on the processing parameters of the twin screw extruder. Moreover the filler dispersion can be related to the total shear strain [γ·t] which is one of the dispersion parameters. An optimized condition for conductivity in these carbon-nanotube (CCNT) filled polymer composites can be determined by this correlation.

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