抄録
Open microcellular foams having small-sized cell and good mechanical properties are desirable for many practical applications. To reduce the cell size of foam, the microcellular foams combining a polybutadiene into the conventional formulation of styrene and water system were prepared via high internal phase emulsion polymerization. Since the material properties of foam are closely related to the solution properties of emulsion state before the polymerization of emulsion into foam begins, the rheological properties of emulsions were investigated using a controlled stress rheometer. The yield stress and the storage modulus increased as the rubber concentration and agitation speed increased, due to the reduced cell size reflecting both a competition between the continuous phase viscosity and the viscosity ratio and an increase of shear force. Based upon the information about rheological properties, the foams were prepared and their morphology and cell sizes were analyzed by a scanning electron microscope. Appreciable tendency was found between the rheological data of emulsions and the cell size change of polymerized foams. The cell size reduction with rubber concentration could be explained by the relation of capillary number and viscosity ratio. A correlative study for the cell size reduction with agitation speed was also attempted and the result was in a good accordance with the hydrodynamic theory.
