Injection Molding Poly(Para-phenylene) with a Rapidly Heated Mold

Abstract

Poly(para-phenylene), a self-reinforced rigid-chain polymer, has superb mechanical properties. Its use as a thermoplastic polymer in injection molding, however, is prohibited because of its extremely high viscosity. In this study, an injection molding process with a rapidly heated mold was used to enhance the moldability. The mold can be heated from room temperature to 250°C in 5 s and thermally cycled for 10,000 cycles without a fatigue failure. The effect of the mold heating temperature on cavity filling was investigated. The status of filling in the cavity was found to be significantly affected by the mold heating temperature. At a mold temperature of 350°C, complete fill of a 4 mm thick and 50 mm long cavity was achieved and the jetted polymer streams in the mold cavity caused by a high injection rate were thermally fused. Rheological data showed that, although it has an extremely high viscosity, poly(para-phenylene) is an extremely pseudoplastic polymer, with its viscosity strongly dependent on the shear rate. These results indicated that poly(para-phenylene) may be practically injection molded at a high injection speed with a rapidly heating mold at a mold temperature well above the polymer's glass transition temperature.