The crystalline phase transformation of poly(vinylidene fluoride) poly(vinyl fluoride) blend films

Poly(vinylidene fluoride) (PVDF), poly(vinyl fluoride) (PVF), and their blends were prepared by solution casting, followed by quenching in ice water after melting to obtain an alpha-crystalline phase. The films were drawn by solid state extrusion at two different drawing temperatures, 50 degrees C and 110 degrees C. The crystalline phases were analyzed by DSC and FTIR. In the undrawn Slims, the content of beta-crystalline phase in the blend of PVDF/PVF 88.5/11.5 was higher than in the PVDF homopolymer, but it was lower than in the PVDF film with a draw ratio higher than 4. The alpha-crystalline phase in PVDF/PVF blends was mostly transformed into the beta-crystalline phase beyond a draw ratio of 4, regardless of the draw temperature and PVF content. The ca-crystalline phase of PVDF systematically transformed into the beta-crystalline phase with increasing draw ratio. The crystallinity of PVDF/PVF blend films drawn at 110 degrees C was higher than those drawn at 50 degrees C. In the drawn blend films, characteristic IR bands of the or form were shifted to those of the beta form and completely changed into those of beta form at draw ratio of 4, regardless of the draw temperature and PVF content.