Rheology and Processing of Tetrafluoroethylene/Hexafluoropropylene Copolymers

Abstract

Abstract The rheology and processing of tetrafluoroethylene/hexafluoropropylene (TFE/HFP) copolymers and TFE/HFP/per-fluoro(alkyl vinyl ether) (TFE/HFP/PAVE) terpolymers, also known as FEP polymers, are reviewed in this paper. Dynamic linear viscoelasticity and other fundamental rheological properties such as the critical molecular weight for the onset of entanglements, Mc, the zero-shear viscosity versus molecular weight relationship, dependence of rheology on thermal history and aspects of shear-induced crystallization are presented. The melt fracture and wall slip behavior of FEP resins is also discussed. Finally, possible processing aids that can be used in the extrusion of FEP resins in order to postpone melt fracture phenomena to higher flow rates are also discussed thoroughly.