UBC Theses and Dissertations
Rheology and processability of teflon FEP resins for wire coating Rozenbaoum, Evgueni E.
Experiments were carried out in both parallel plate and capillary rheometers for a variety of tetrafluoroethylene/hexafluoropropylene (TFE/HFP) copolymers and TFE/HFP/per-fluoro(alkyl vinyl ether) (TFE/HFP/PAVE) terpolymers, also known as Teflon® FEP polymers, having different molecular weights and compositions (HFP and PAVE content). The critical conditions for the onset of melt fracture and the influence of temperature, molecular weight, and composition of the resins are determined. The critical molecular weight for the onset of entanglements was found to be about 100,000, a value much higher than those previously reported. The relationships between the processability of the wire coating Teflon® FEP resins and their composition, viscosity, ability to crystallize, and melt elasticity were established. The experimental data were used for a thorough rheological modeling of the behavior of these resins. The latter includes calculation of their linear relaxation time spectra and nonlinear parameters using a multimode Phan-Thien and Tanner (PTT) constitutive equation. A new data analysis procedure based on a mathematical model for the nonisothermal capillary flow of polymer melts coupled with heat transfer is developed. The computer simulations proposed can be used to provide detailed velocity, temperature, and pressure distributions and to recover the parameters of the employed slip velocity model corrected for the effect of viscous heating. Finally, the effect of various processing aids on the processability of fluoropolymers and polyolefins during extrusion and wire coating was studied. It was found that polyethylene works as a processing aid in the extrusion of Teflon® FEP resins in the same way as fluoropolymers do in the extrusion of polyolefins. Finally, the processing additive based on a boron nitride (BN) composition was found to eliminate sharkskin melt fracture and postpone gross melt fracture to significantly higher shear rates for a variety of polymers.
Item Citations and Data