Structural and morphological changes at initial state under uniaxial elongation of rolled polytetrafluoroethylene

Abstract

Polytetrafluoroethylene (PTFE) membranes, which are prepared by a biaxial stretching process of rolled sheets, have a porosity structure consisting of nodes and fibrils, and exhibits a unique mechanical behavior. We investigated the differences in deformation behavior of rolled PTFE sheets between the rolling and the cross directions using synchrotron radiation in situ WAXD and in situ SAXS measurements. The mechanical anisotropy for rolled PTFE sheets results from a planar or strip-biaxial deformation mode. The rolled PTFE sheets showed an extended chain crystal (ECC) structure. According to in situ WAXD profiles and 2D-SAXS patterns during deformation, the stretching in the rolling direction (RD) causes the fibrillation accompanied with the mechanical yielding, at which the stretching in the RD resulted in pore expansion and lattice distortion rather than obvious chain orientation. The direction of the pore expansion changed to the cross direction (CD) when stretching perpendicular to the RD. We found a positive dependence between the pore size in CD and the average molecular weight of PTFE sheets.

Keywords

• Tensile properties
• Polytetrafluoroethylene
• In-situ WAXD
• In-situ SAXS
• Molecular weight