AND THE DESIGN OF A MICROCELLULAR FOAM

Microcellular plastics are foamed plastics characterized by cell sizes smaller than 10 p.m and cell densities in excess of 109 cells/cm 3. This thesis addresses microcellular polymer processing in the context of the wire coating industry. Due to their exceptionally low dielectric constants, fluoropolymers commonly serve as the dielectric insulation in coaxial cables. A microcellular coating of such materials on the cable can significantly improve electrical performance. The first phase of research identified the key microcellular processing parameters for two different semicrystalline fluoropolymers, DuPont FEP 4100 and DuPont PFA 440 HP. In addition, weight gain experimentation revealed that both polymers exhibited induced crystallinity as a result of carbon dioxide sorption. The second phase of research implemented a newly designed scaled-up microcellular foam extrusion system featuring a gear pump as the cell nucleation device. Preliminary experimentation with Union Carbide DFD-6005 Natural low density polyethylene and Quantum Petrothene 1610-PF polypropylene revealed that gear pump nucleation produced submicron-sized cells which were neither affected by gear teeth memory effects nor shear effects in the wir