Where is the glass transition temperature of poly(tetrafluoroethylene)? A new approach by dynamic rheometry and mechanical tests

Abstract

Polytetrafluoroethylene (PTFE) has been used for many years in different application fields 2 due to its outstanding chemical and physical properties. But, the value of its glass transition 3 temperature is still today a matter of controversy and very different values are proposed in the 4 literature. This paper proposes to answer to this scientific question using dynamic mechanical 5 measurements. First, the viscoelastic properties of PTFE are described on a large temperature 6 range and the influence of the shearing frequency is carefully investigated. Then, the effects 7 produced by the polymer annealing on its thermomechanical behavior are detailed. This study 8 comforts the idea that PTFE amorphous phase should be considered as comprised of two 9 distinct regions. The first one named "mobile amorphous fraction" (MAF) is able to relax at 10 low temperature (T =-103 °C). The other one is specific of the macromolecular segments 11 present at the boundaries between crystalline and amorphous domains. Due to the close 12 vicinity of the crystallites, these macromolecular segments present a more restricted mobility. 13 The corresponding phase is designated as the "rigid amorphous fraction" (RAF) and its 14 mechanical relaxation produces itself at higher temperature (T = 116 °C). Actually, this latter 15 value is strongly dependent on the material crystallinity degree. In particular, it is shifted to 16 higher temperature after occurrence of a recrystallization that is accompanied by a further 17 reduction of the RAF's dynamic. Instead, the characteristics of the MAF relaxation are poorly 18 affected. Tensile tests also support that the "real" T g of the polymer is located at low 19 temperature. All these results have been compared to those of the literature to propose a real 20 scientific discussion and to understand the origin of somewhat contradictory interpretations.

Thermal, Viscoelastic, Mechanical and Wear Behaviour of Nanoparticle Filled Polytetrafluoroethylene: A Comparison

“…The three significant peaks of tangent delta can be found at −95–85 °C, 18–20 °C and 117–121 °C temperature, depending on the given material ( Figure 6 and Table 3 ). This is in agreement with the literature [ 20 ]. The temperature peaks correspond to phase transitions of PTFE: The first peak is the γ-transition, the second one is the β-transition while the third one is the α-transition [ 20 ].…”

Correlation between gas transport properties and the morphology/dynamics of crystalline fluorinated copolymer membranes

“…We focused on the temperature dependence of the viscoelastic properties between 30 and 150 °C. The evolution of the storage modulus E′ and the loss modulus E″ is consistent with the literature reports . On the basis of the peak position in the plot of tan δ (= E′ / E″ ) as a function of temperature, we estimated that the glass‐transition temperature ( T g ) of the PFA membranes was 85 °C.…”

Preparation and properties of porous polytetrafluoroethylene hollow fiber membrane through mechanical operations

“…The onset temperature was 329°C, which was melting point of PTFE. And, mechanical relaxation of PTFE rigid amorphous fraction produced at temperature of 116°C . Yang et al .…”