FTIR studies of β-phase crystal formation in stretched PVDF films

Poly vinylidene fluoride (PVDF) is a semi-crystalline polymer which shows polymorphism and is commonly crystallized in non-polar crystalline alpha-phase. It has found various applications during the last decades and the most important applications lies in its pyro- and piezoelectric properties. The beta-phase content is of prime importance in these applications so that increasing beta-phase content of the polymer has always been of great concern in this field. Calorimetric studies and FTIR spectra show the appearance of beta-phase in compression molded films of two different grades of PVDF resin. beta-phase formation is more evident in stretched films by a transformation mechanism of alpha to beta-phase via the formation of a necking region during stretching. By using FTIR techniques, a maximum content of 74% for beta-phase was calculated. This was achieved during stretching at 90 degreesC and for a stretch ratio between 4.5 and 5. FTIIR spectra offer a precise method for detecting the variations of beta-phase in polymer films. (C) 2003 Elsevier Science Ltd. All rights reserved.