Piezoelectric And Pyroelectric Properties Of Pvdf Fiber

Piezoelectricity is a phenomenon when a mechanical stress is applied to some piezoelectric material; electrical charges appear between its two opposite sides. Conversely, if an electrical field is applied to this material, it will generate mechanical strain. Also, for material showing Pyroelectric properties, electric charges will appear under the effect of temperature. According to these proprieties, a piezoelectric element is an electromechanical transducer (energy converter). At present, most of the piezoelectric material is film or ceramic cylinder. The soft piezoelectric fiber is not reported. As a piezoelectric polymer, PVDF (polyvinylindine fluoride) has many advantages, many due to its mechanical properties, such as flexibility, high mechanical resistance, and dimensional stability. PVDF is a piezoelectric polymer, which was studied systematically and was applied extensively.The research studies how to melt-spin PVDF fibers and polarize the fibers. It is an object to choose the PVDF material, probe melt-spinning technology parameters; and improve the spinning ability of PVDF. Then the fiber was polarized and the effect of poling parameters on microstructure was studied.The research prepared PVDF fibers using melt spinning. PVDF is semi-crystalline polymer, and its molecule chain is linear and soft. Manufacturing fibers is feasible theoretically, however it is hard in reality and increasing the temperature cannot improve the spinning ability of PVDF. PA 11 is suitable for manufacturing fibers; so two-polymer blend fibers were prepared. According to piezoelectricity and spinning property, we found the optimal proportion of two composites, and 50wt/50wt PVDF/PA11 fibers were suitable. Because of the crystalline leading to the piezoelectricity of PVDF, PVDF fiber and PVDF/PA11 fiber's structures and crystalline were investigated and analyzed by means of Wide angle X-ray Diffraction, Differential Scanning Calorimetry, Fourier Transmittance Infra-red Spectroscopy and Scanning Electron Microscopy, etc. It was shown that there are two kinds of crystalline- a phase and B phase in PVDF fiber. The a phase can change to B phase by stretching. In the range of low temperature the higher content of B crystalline was achieved during the higher drawing ratio and the higherdrawing temperature. In the blend fiber, stretching benefit to phase transiting of PVDF, but not PA11, and quenching benefit to phase transiting of PA 11, but not PVDF.After designing poling equipments, fibers were polarized. The microstructure changes of the fibers were studied by means of DSC, FTIR and SEM. The results show that: the fiber was polarized in dimethyl silicone fluid, and the microstructure changed. The microcrystalline was same to the direction of electric field. The microcrystalline orientation of the film that was obtained by Melting PVDF congealing in the effect of electric field changed along electric field obviously. Comparing with the film congealing without electric field their crystalline plate become thick. FTIR absorbance of the polarized fiber decreases than that of the fiber before polarized.