M.S. Thesis Presentation by Bret Alan Rodeheaver
Thursday, June 10, 1999

(Dr. Jonathan Colton, advisor)

"Open-Celled Microcellular Thermoplastic Foams"

Abstract

Because thermoplastics have high fracture toughness, high strain to failure, low electrical conductivity and high chemical resistance, they are the preferred materials for microporous applications, such as blood oxygenators, biological membranes and battery separators.  The need exists for an environmentally clean, simple process that produces microporous foam in a variety of thermoplastics.  A technique has been well established that uses an environmentally benign blowing gas to generate closed-celled microcellular foam.  This thesis determined the conditions necessary to form open-celled structure in foams produced by this technique.

The morphology of microcellular foam produced by this technique typically developed thin cell walls where bubbles impinged.  A bubble coalescence model was used to predict a range of processing conditions that promoted the spontaneous rupture of these thin cell walls.  Samples were foamed under these conditions using the batch processing method.  The foam structure was analyzed with scanning electron microscopy and mercury porosimetry.  The effects of the processing conditions on bubble coalescence were determined.  Pores were observed in the cell walls of samples formed at four different conditions.  Two of these samples, saturated at 2500 psig and foamed at 200?C for 1 and 2 seconds, had pore sizes less than 1 ?m in diameter.  The analysis verified that this foaming technique produced open-celled microcellular foam spontaneously under the processing conditions predicted by the bubble coalescence model.