Processing‐Property interactions in vinylidene fluoride/trifluoroethylene random copolymers

The effect of flow history, processing temperature, and exit draw ratio have been studied for copolymers of vinylidene fluoride/trifluoroethylene of molar compositions 66/34 and 75/25%. The copolymers were extruded through an impinging channels film die which produces a mixed extension and shearing flow as well as a slit die. Stress fields during flow were measured using flow birefringence. Differential Scanning Calorimetry (DSC) analyses were used to characterize the thermal behavior; and flat film and Wide Angle X‐ray Scattering (WAXS) were used to evaluate the crystal structure and morphology of the extrudates. Extensional melt stresses on the order of 6.35 × 10 5 Pa were necessary to induce sufficient orientation for crystallization of water‐cooled 66/34 mol % copolymers into the all‐trans configuration. Preorientation of the melt by extensional stresses enhanced the transformation of the 3/1 helical to an all‐trans structure in the 66/34 copolymer as well as producing a more compact unit cell in the 75/25 mol % copolymer leading to as much as a 7°C higher Curie transition temperature.