Solid-state processing of poly(tetrafluoroethylene): Simulation of sintering cycle

The powder processing of polymers involves compaction of the polymeric powders followed by sintering of the compacted preforms at temperatures above the melting point of the polymer. The properties of the finished products are dependent on the process parameters used during compaction and sintering. In the case of semi–crystalline polymers, the properties are governed by the crystalline morphology developed during the sintering cycle. The crystalline morphology developed during cooling of the sintered product is influenced by the crystallization rate/crystallization temperature and in turn by the temperature profiles across the cross–section of the product. This paper presents the results of computer simulation of temperature profiles during the sintering cycle of PTFE billets using heat transfer equations. The effect of sample geometry, materials properties and modification of sintering cycle on the temperature profiles have been discussed with respect to the physical processes which take place during the sintering cycle. The implications of the temperature gradients developed during the process on the structure development and moulded product properties are discussed.