α to β Phase Transformation and Microestructural Changes of PVDF Films Induced by Uniaxial Stretch

Abstract The phase transformation from α to β poly(vinylidene fluoride) (PVDF) through a stretching process at different temperatures was investigated. Samples of originally α-PVDF were stretched uniaxially at different temperatures at draw ratios from 1 to 5. The stretched samples were studied and characterized by infrared spectroscopy, scanning electron microscopy, and differential scanning calorimetry. The maximum β-phase content was achieved at 80°C and a stretch ratio of 5, but the samples still showed 20% of the original α-phase. Accompanying the phase transformation, an orientation of the polymer chains was observed. The stretching process also influenced the degree of crystallinity of the polymer. Poling of the samples also improves the α- to β-phase transformation. Keywords: ferroelectricsmechanical propertiesphase transformationpolymersPVDFstretchingPACS: 82.35.Lr77.84.Jd64.70.km68.37.Hk81.70.Pg62.20.de Acknowledgements The authors thank the EU-ALFA project Plastinet for a mobility grant for completing experimental work at the Universidade Federal de São Carlos (Brazil), the GRICES/FAPESP (Proc. 4.1.3/FAPESP) for program support, and the Portuguese FCT for Grants POCI/CTM/59425/2004 and SFRH/BD/16543/2004; thanks to Dante L. Chinaglia from UNESP-Rio Claro for the use of his laboratory.