Viscosity of Ethylene/Tetrafluoroethylene Alternating Copolymers

摘要

Low shear rate viscosity measurements of alternating copolymers of ethylene andtetrafluoroethylene (PETFE) melts have been performed at different temperatures by using the centrifuge ball viscometer. The viscosity eta (Pa s) could be obtained with an empirical relation, ac=(4.29+/-0.08) x 10(exp 2)(eta Vx)(0.856+/-004), with ac and Vx, being, respectively, the acceleration (g = 9.8 m/s squared) and the terminal velocity (m/s) of a stainless steel ball of 1.5 mm diameter moving in the polymer melt, which was flame sealed in a horizontal cylindrical glass tube of 4.26 mm diameter. For the temperature dependence of the viscosity, an activation energy E sub a of 15.3 kcal /mol was determined. The activation energy for PETFE is between 5.7-14.6 kcal /mol for polyethylene (PE) and 18-36 kcal /mol for tetrafluoroethylene (PTFE). A relationship between the zero shear rate viscosity eta sub o (Pa s) and the molecular weight Mw (g /mol) of PETFE copolymer melts at 280 deg C (eta sub o=(1.23 +/-0.02) x 10(exp -16(Mw)(3.43+/-0.06)) should permit us to determine the molecular weight of PETFE with the centrifuge ball viscometer.