The heat transfer characteristics of PTFE during quasiadiabatic decompression in nitrogen gas

This article describes a series of experiments which elucidate the origin of a previously reported apparent plasticization of PTFE under a high pressure N 2 environment. The results indicate that, to a first order, the apparent plasticization process is associated with the heat generated following a near adiabatic compression of the pressure environment; it is not a true isothermal plasticization in the conventional sense. The processes which contribute to this phenomenon involve subtle effects which are explored in some detail. Particularly important is the surprisingly high efficiency of the compressed gaseous media as heat transfer fluxes for intrinsically poor thermal conductors such as organic polymers. Other factors include the thermal conductivity of the gas and its heat capacity. In addition, the polymer itself manifests an intrinsic increase in its thermal conductivity due to the action of the triaxial stress. The overall temperature rise due to gas compression is very large and for N 2 long sustained. The work done on the polymer by simple triaxial compression is trivial in comparison; studies in liquid media confirm this to be the case. A less extensive treatment, along similar lines, is described for the decompression of gaseous media. The combined action of gas compression and decompression together with the associated thermal cycles are briefly discussed in the context of polymer processing and the behavior of PTFE compression seals.