Effect of drawing on the molecular orientation and polymorphism of melt‐spun polyvinylidene fluoride fibers: Toward the development of piezoelectric force sensors

Thin piezoelectric polyvinylidene fluoride fibers containing a high piezoelectric -phase content of up to 80% were developed in this work using a melt-spinning process. After crystallization from the melt, the fibers were subsequently stretched unidirectionally at 120 degrees C between 25 and 75% of their original length. The effects on the molecular orientation, polymorphism and tensile properties of the fibers were investigated. Polarized infra-red spectroscopy and X-ray diffraction results show that the conversion of -phase to -phase occurred during the stretching process as a result of molecular alignment and creation of a dipole induced by the CF2 groups normal to the fiber direction. These fibers were then integrated into various weave architectures in order to design flexible two-dimensional textile-based piezoelectric force sensors. The piezoelectric responsiveness of these materials, tested under impact (70 Newton force, 1 Hz frequency) was very promising, with a maximum output voltage of up to 6 V and an average sensitivity of up to 55 mV/N measured. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013