Emulsion polymerization of tetrafluoroethylene: effects of reaction conditions on particle formation

Abstract

The emulsion polymerization of TFE was carried out with a surfactant (FC-143) and an initiator (ammonium persulfate) under various reaction conditions. Two different shapes of PTFE dispersion particles were produced by the emulsion polymerization, rods and spherical particles. Variables, except for surfactant concentration, do not affect the initial and final particle morphology when no coagulation occurs. Rod-like particles are formed when the surfactant concentration is near or above the critical micelle concentration (CMC) of the surfactant. At below CMC, however, spherical particles are dominant. No hexagon-shaped particles or abrupt changes in the particle morphology are observed during polymerization. When no coagulation occurred, the size and number of polymer particles suddenly increased in the early stages of emulsion polymerization and then steadily increased as time progressed. Most particles are formed in the early stages (within 5 min), and the size of particles formed was in the range 60-80 nm in diameter. The particle sizes ranged from 100 to 230 nm at 250 g/l of a specific TFE uptake concentration (the PTFE dispersion had a solid content of about 20%). It was found that the size and number of polymer particles formed are almost independent of the temperature, pressure, concentration of initiator and stabilizer (anti-coagulant), whereas the surfactant concentration, kinds of stabilizer, and agitation speed are important. The particle size decreased gradually as the dispersion concentration increased, whereas the particle number increased exponentially. When the PTFE dispersion coagulated during polymerization under certain conditions (high temperature and agitation speed, and low concentration of surfactant), the particle size suddenly increased, the particle number suddenly decreased, and the rate of the polymerization decreased, indicating that the polymerization occurred on the surface of the polymer particles. (C) 1999 Elsevier Science S.A. All rights reserved.