Solid-State Extrusion of Poly(tetrafluoroethylene) Nascent Powder.

Abstract

Poly (tetrafluoroethylene) (PTFE) nascent powder was drawn by solid-state extrusion to extrusion draw ratios (EDR) ≤ 100 in the temperature (Te) range of 100~340°C, which covers the Tg(125 °C) and the ambient Tm(334°C). At a given Te, the maximum achievable EDR (EDRmax) increased with increasing shear rate (γ) and hence extrusion rate (Ve), reaching a maximum at a γ of 1 ˜ 4×104/min (V e of 300 ˜ 600 cm/minjdepending on the Te, and at yet higher γ's, the EDRmax decreased rapidly due to the formation of flaws. At a given γ, the EDRmax increased with increasing Te up to a Te =340°C. At Te's >340°C, the drawability was lost due to melting. The structure and properties of extruded products were complexly affected by the extrusion variables. Thus, the oriented rods having crystalline chain orientation function fc of 0.75˜0.96 and flexural modulus Ef of 7.5 ˜ 15 GPa at 24°C could be obtained by extrusion at an optimum Te of 340°C and a Ve of 1˜1000 cm/min (γ of 1×10˜1×105/min). These results show that nascent PTFE powder could be solid-state extruded at remarkably higher Ve's than other polymers, reflecting the less entangled morphology of the nascent powder and the high ductility of a PTFE crystal due to the week intermolecular interaction.