Melt rheological properties of ETFE: an attempt to illuminate the fluorine-substitution effect

Flow behaviors and rheological properties of ethylene tetrafluoroethylene alternating copolymer (ETFE) under high-shear conditions were first reported. Flow instabilities, shear and extensional viscosities, and die swell of ETFE were investigated. Rheological behaviors of perfluorinated ethylene propylene copolymers (FEP), partially fluorinated ETFE, and non-fluorinated polyethylenes (PE) were compared for understanding the role of fluorine incursion on materials properties. It is found that (1) ETFE does not have sharkskin region or second smooth region which frequently occurs in FEP and linear PE; (2) critical shear stresses at which surface melt fracture occurs for the three polymers follow the order: FEP < ETFE < PE; (3) stable flow region narrows, die swell weakens, and flow activation energy increases when fluorine content of polymer increases. After time–temperature superposition, shifted shear viscosity, extensional viscosity, and elastic data (die swell) present universal scaling characteristic and superpose well in term of the same shift factors.