Development of the crystal structure of polytetrafluoroethylene in the forming process during paste extrusion and the effect on fiber properties

Abstract

Paste extrusion is recognized as one of the important methods for forming polytetrafluoroethylene (PTFE) fibers, and the properties of PTFE fibers are closely linked to their structure. This paper analyzes the dynamic changes in the crystal structure throughout the entire process, which includes the combination of PTFE raw materials and lubricant, the aging of PTFE pastes, the extrusion process, as well as sintering, drawing, and shaping.Systematic research has shown that a lower crystallinity of PTFE is more beneficial for the maturation of the paste, and the proportion of folded chains in PTFE is negatively correlated with the decrease in enthalpy of crystal transformation. The critical influence of (107) and (108) pyramidal crystal planes during the extrusion process was demonstrated through wide-angle X-ray diffraction (WAXD). It is found that an increase in crystal size leads to greater internal resistance that is unfavorable to paste flow, and significant changes in crystal size are observed under constant-speed, high-pressure extrusion, characterized by an increase in pyramidal crystal planes and a decrease in prismatic crystal planes. Small-angle X-ray scattering (SAXS) shows that the PTFE long period is not affected by the high-pressure extrusion process, but rather increases after sintering and drafting. These findings offer a vital crystallographic insight into optimizing the PTFE extrusion process. Through the regulation of grain size and structure of molecular chainthe processing conditions and final properties of PTFE can be effectively improved, thereby promoting wider applications and technological progress in the field of high-performance polymers.