Determination Of Molecular Weight And Its Distribution Of FEP By Dynamic Rheology Method

Tetrafluoroethylene-Hexafluoropropylene Copolymers (FEP) is a kind of broadly used polymer materials. Because of hardly soluble in any solvent, it is difficult to obtain its molecular weight and distribution. Here dynamic rheology method is adopted to determinate the molecular weight and its distribution of four FEP samples.Through dynamic melt viscoelastic tests, the rheometer can give the curves of complex viscosity changing with frequency. Fitting the experiment data with Carreau-Yasuda equation, the zero-shear viscosity could be obtained. Then the weight average molecular weight of four FEPs could be gained for the well-known relationship of molecular weight and zero-shear viscosity.It is easy to get the curves of dynamic modulus and frequency. In this thesis, we used Tuminello modulus model to obtain the weight-fraction differential molecular weight distribution of four samples. Fitting the experimental curve of dynamic modulus with Maxwell-Wiechcert model, we got the plateau modulus of FEP. According to the theory of rheology, a new way to estimate of the prefactor of the relationship of molecular weight and dynamic frequency was given. Fitting the curves of weight-fraction differential molecular weight distribution of the FEPs obtained by Tuminello model with three-parameter Log-Normal function, and then the result was rescaled and normalized. Finally the function of rescaling factor, normalization factor and polydispersity index was given.Moreover, we also attempt to obtain the molecular weight distribution of FEPs by Tuminello viscosity model and compared with Tuminello modulus model. It is found that the results were not identical. However, the tendency is the same: the molecular weight distribution of FEP-1 is broader than that of FEP-2.