Background Information about PTFE

The synthesis and properties of PTFE have been well described by Sperati and Starkweather and Sheratt Two books on fluorine-containing materials are also useful. The history of die discovery and development of PTFE has been documented by Plunkett and by Sperati. Polytetrafluoroethylene is a highly 

Measurements by many researchers have shown that PTFE s equilibrium melting temperature is 327°C. ° Once it is heated above its melting temperature, its initial properties are irrecoverable. Compaction of PTFE powder and heating above 327°C results in a partially crystalline solid polymer composed of large crystals with a coexisting noncrystalline phase. Crystal size and perfection depend on die crystallization conditions slow cooling results in larger, more perfect crystals. On this point, we present detailed information from electron microscopy, corroborated by measurements of X-ray line breadth. 

The rate of cooling from above the melting temperature has significant effects on lamellar thickness and perfection as well as on physical properties. There is a progressive increase in lamellar thickness and measured density with slower rates of cooling from 380°C. Quenched specimens, in our work, have a specific gravity of 2.136 g/cm compared to 2.180 0.003 for specimens cooled at die very slow rate of 0.02 deg/min. Annealing a quenched sample for 5 hours at 312°C causes die density to increase to 2.158 g/cm. For perspective, the density of totally noncrystalline PTFE is estimated to be 2.00 and the perfect-crystal density is 2.301 g/cm by X-ray diffraction. 

Much attention has been devoted to the two first-order phase transformations that PTFE shows at 19 and 30°C. Attention has been focused on elucidating the mechanism of transformation and its kinetics. 

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In the first paper on fluorocarbon polymers in this Symposium [Ij, Dr. Plunkett described the details about his discovery of polytetrafluoroethyl-ene scientific understanding about the polymer, and brief mention of a few recent studies. Even in this published version of the paper from the Syn sium, it is not feasible to cover the history in any sort of detail. Therefore, this paper can only outline the general background, with sufficient references to the literature so that detailed information will be readily accessible. The references, shown within r ], are selective, rather than exhaustive, leading the reader to some of the many people who made PTFE the important material it is. Usually a reference is made to a pioneering patent or paper rather than to many that followed. 

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