Melt processability of polytetrafluoroethylene: Effect of melt treatment on tensile deformation mechanism

摘要

It is widely accepted that the melt processibility of polytetrafluoroethylene (PTFE) is poor. In this article, a high-molecular-weight PTFE was extruded smoothly with a modified die; and critical shear rate could be raised to 4 s~(-1), using a die with L/D (length to diameter) ratio of 200. Meanwhile, we compared the current PTFE fiber spinning method with melt spinning to investigate the effects of high-temperature treatment on the drawability of PTFE and found that the processing sequence could play a key role. The deformation imposed before or after the high-temperature treatment could determine whether the fibrillation can be achieved continuously and effectively. Based on the experiment phenomenon, together with the results of differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy characterization, we proposed a model to describe the submicron structural change of PTFE during extension. From this model, the fundamental mechanism for the poor melt processibility of PTFE was elucidated.