Some rheological properties of molten polytetrafluoroethylene

✍ Scribed by G. Ajroldi; C. Garbuglio; M. Ragazzini

• Publisher: John Wiley and Sons
• Year: 1970
• Tongue: English
• Weight: 446 KB
• Volume: 14
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/app.1970.070140109

✦ Synopsis

Measurements of melt viscosity on samples of polytetrafluoroethylene of difTerent molecular weight were carried out at 360°C by means of tensile creep tests in the linear viscoelasticity range. The apparent activation energy for viscous flow in the range between 330" and 380°C was estimated to be 20 kcal/mole. A value of about 7,500 was also determined for the average molecular weight between entanglement points ( M J , from the equilibrium compliance (Ds). Melt viscosity data were compared with zero strength time (ZST) values and a linear correlation was found on a bilogarithmic scale. The dependence of ZST on the applied stress and temperature was also studied and the results are discussed on the basis of Bueche's theory on the creep at rupture above the glass transition temperature.