Analysing the relaxation behaviour of poly(tetrafluoroethylene) in the α-transition region by applying a two-component model

Abstract

Semicrystalline polymers play an important role as materials for engineering purposes. Such a polymer is poly(tetrafluoroethylene) (PTFE), for which Araki investigated the compressive relaxation behaviour at temperatures between 60 and 150°C and met major difficulties in achieving a satisfactory systemization of his curves when using the principles of thermorheologically simple materials. The objective of this study is to investigate whether an improved systemization can be achieved on the basis of a two-component (TC) model containing an elastic component and a viscous component corresponding to the crystalline phase and the restricted amorphous phase in PTFE, respectively. The properties of the components show pronounced temperature dependence characterized by three different transition temperatures and activation energy distributions. To check the consistency of the model approach, tan δ was calculated on the basis of theoretical parameter values and compared with experimental data taken from the literature. Prediction and experiment agree to an extent where even the fine structure of the tan δ peak for the α-transition is reproduced. The investigation thus shows that the compressive relaxation curves measured by Araki are consistently described by the TC model, leading to the detection and description of three individual transitions that govern the overall viscoelastic performance of PTFE in the α-transition region.