THE EFFECT OF LIQUID ENVIRONMENTS ON THE TENSILE DRAWING OF POLY(TETRAFLUOROETHYLENE) AND TETRAFLUOROETHYLENE-HEXAFLUOROPROPYLENE COPOLYMERIN A WIDE TEMPERATURE-RANGE

The development of microporous structures during the tensile drawing o f fluoropolymers in air and in liquid environments was studied in the temperature range extending from +22 to -196 degrees C. The results of mechanical tests were compared with the data of gas permeability, X-r ay analysis, and direct microscopic observations. Tensile drawing of h ighly crystalline PTFE in the presence of organic liquid environments at room temperature is accompanied by the formation of a well-develope d system of open micropores with the Knudsen dimensions. This is a res ult of intercrystallite (delocalized) crazing. In PTFE amorphized by q uenching from melt and in tetrafluoroethylene-hexafluoropropylene copo lymer, the development of micropores induced by tensile drawing is pro vided by the development of classical crazes. The development of craze s is controlled by the diffusion rate of liquids into the stressed pol ymer regions; that is, this process is associated with the local plast icization of microregions where deformation proceeds.