New technique of processing highly oriented poly(vinylidene fluoride) films exclusively in the β phase

Oriented beta-phase films were obtained by utilizing two different techniques: conventional uniaxial drawing at 80 degrees C of predominantly alpha-phase films, and by drawing almost exclusively beta-phase films obtained by crystallization at 60 degrees C from dimethylformamide (DMF) solution with subsequent pressing. Wide angle X-ray diffraction (WAXD) and pole figure plots showed that with the conventional drawing technique films oriented at a ratio (R) of 5 still contained about 20% of phase alpha, a crystallinity degree of 40% and beta-phase crystallographic c-axis orientation factor of 0.655. Drawing at 90 degrees C and with R = 4 of originally beta-phase films results in exclusively beta-phase films with crystallinity degree of 45% and orientation factor of 0.885. Crystalline phase, crystallinity degree, and crystallographic c-axis orientation factor of both phases were also determined for alpha-phase oriented films obtained by drawing alpha-phase films at 140 degrees C. For films drawn at 140 degrees C the alpha to beta phase transition drops to about 22%. Reduction in crystallinity degree with increasing R is more pronounced at draw temperature of 140 degrees C compared with 80 degrees C. Moreover, for both phases the c-axis orientation parallel to the draw direction is higher at draw temperature of 140 degrees C than at 80 degrees C. (c) 2007 Wiley Periodicals, Inc.