Structure and Deformational Behavior of Poly(vinylidene fluoride) Hard Elastic Films (original) (raw)
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Journal of Polymer Research, 2011
The phase transformation from the α-to the electroactive β-phase of poly(vinylidene fluoride) (PVDF) extruded filaments submitted to different stretching conditions was investigated. Sample filaments of α-PVDF thermoplastic were extruded and stretched uniaxially at different temperatures (80 ºC to 120 ºC) and stretch ratios (1 to 6). The stretched samples were studied and characterised by x-ray diffraction and quasi-static mechanical experiments. High β-phase contents (~ 80%) are achieved using a stretch ratio of 5 independently of the stretching temperature, between 80 ºC and 120 ºC. Subsequently, in order to obtain filament geometries and material configurations suitable for application, a two layer filament with coaxial layers was produced by coextrusion. The inner layer consisted of a commercially available grade of a conductive thermoplastic with a polypropylene (PP) matrix. For the outer layer the same grade of PVDF was employed. The double-layer filament was also stretched under the same conditions of the PVDF filaments and the results obtained shows that the inner layer material, acting as an electrode, does not have any influence in the PVDF 2 crystallization process: PVDF crystallizes in the α-phase for stretch ratios of 1 and the α− to β-phase transformation occurs for higher stretch ratios.
Fracture analysis of annealed PVDF films
Polymer Testing, 2008
The effect of annealing 50 mm thick, extruded poly(vinylidene fluoride) films in a form (a-PVDF) was investigated by differential scanning calorimetry and mechanical testing on unnotched and double-edge notched tensile specimens. As to the fracture behavior, micromechanisms of cavitation, spherulite breakdown, fiber bundle structure formation and ato b-phase transformation were detected. The progressive structural evolution taking place during annealing affected the deformation and fracture behavior significantly. While the annealing-induced subtle distinctions in microstructure are slightly reflected by the determined mechanical and essential work of fracture (EWF) properties, a distinct differentiation was possible by analysis of the process zone. A correlation between characteristic values of the process zone at necking and the endothermic transitions due to secondary crystallization determined by differential scanning calorimetry (DSC) was established. Annealing of PVDF films facilitates the micromechanism of cavitation, which is presumably related to perfection of morphological superstructures (spherulites) and, thus, interspherulitic stress concentration and failure.
Polymer, 2001
The present work focuses on the effects of thermomechanical history on the structure and mechanical behaviour of PVDF. In the ®rst part of our investigation differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) are used to follow the evolution of the structure of PVDF after different annealing treatments or deformation. Processing has a signi®cant impact on the quantities of the amorphous and crystalline phases and their interphase. Subsequent annealing affects these phases in a different proportion. This in¯uence depends on the position of the annealing temperature in comparison with the upper glass transition temperature of PVDF. Deformation induces conformational change in the injection moulded samples. Thus, the a conformation is transformed to the b conformation. The b conformation also has a noticeable in¯uence on the mechanical behaviour of the material, which will be discussed in the second part of our study.
Poly (vinylidene fluoride) Thin Film Prepared by Roll Hot Press
Various methods have been developed in the manufacture of Poly (vinylidene fluoride) (PVDF) thin films such as coating, spreading, evaporation and calendaring. The method of making this film certainly has many advantages and disadvantages as in the case of operational processes and also the cost of the required treatment. In this paper, an alternative method to preparation of PVDF thin films has been done through the development calendaring method by using roll hot press. The advantages of roll hot press are simple in terms of operation and relative low cost. PVDF thin film has been produced for several temperatures of roll hot press with several different thicknesses. The PVDF thin films are characterized using X-Ray Diffraction and IR spectra. In addition to determine the surface resistivity are caried out using I-V meter. We found that an increase in β fraction of PVDF thin films with increasing temperature at fixed film thickness, while the surface resistivity of PVDF film are decreased. This shown that the piezoelectric property of PVDF films has been improved.
Properties of PVDF films stretched in machine direction
Polymers and Polymer Composites, 2020
Polyvinylidene fluoride (PVDF) films possess superior piezoelectric properties due to the β-phase obtained by methods, such as addition of nanofillers, application of high electric field, use of polar solvents and mechanical stretching. Simultaneous stretching and heating of the films can reduce porosity, increase transformation from α-phase to β-phase, and hence, improve their piezoelectric properties. This article presents the effects of stretching PVDF films on the β-phase formation and the resulting mechanical properties. A custom-designed stretching unit with roller mechanism and heating provision was employed for the purpose. The 200% stretched films at 100°C showed 86.79% β-phase, which is in correlation with X-ray diffraction peaks at 2 θ = 20.3–20.6°. Transmission electron microscopy and scanning electron microscopy of the stretched films revealed spherulitic to lamellar transformation and decrease in porosity. Stretching increased crystallinity from 32.99% to 44.84%. Nanoi...
Thin films of poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) were prepared using solvent cast method and characterized for structural, mechanical and surface morphological properties to investigate the presence of β-phase through X-ray diffraction, scanning electron microscopy, differential scanning calorimeter, Raman and Infrared spectra, and tensile testing. The conditions to achieve β-phase of P(VDF-TrFE) have been discussed in detail. Following the material characterization, the fabricated β-phase P(VDF-TrFE) sensors have been tested for dynamic strain sensing application. Time response from the βphase P(VDF-TrFE) sensor due to the free vibration and impact on beam structure is obtained and is compared with β-phase PVDF sensor and conventional piezoelectric wafer type sensor. The variations in the frequency response spectra due to free vibration and impact loading conditions are also reported, which reveal the fact that the sensitivity of the β-phase P(VDF-TrFE) sensor to various modes of vibration is same as the β-phase PVDF sensor. The resonant and anti-resonant peaks in the frequency response of βphase P(VDF-TrFE) films match well with that of βphase PVDF sensor and Lead zirconate titanate (PZT) wafer sensors. Thus the fabricated β-phase P(VDF-TrFE) sensors can be effectively used as the dynamic strain sensor.
The beta-phase of polyvinylidene fluoride (PVDF) is well known for its piezoelectric properties. PVDF films have been developed using solvent cast method. The films thus produced are in alpha-phase. The alpha-phase is transformed to piezoelectric beta-phase when the film is hot stretched with various different stretching factors at various different temperatures. The films are then characterized in terms of their mechanical properties and surface morphological changes during the transformation from alpha- to beta-phases by using X-ray diffraction, differential, scanning calorimeter, Raman spectra, Infrared spectra, tensile testing, and scanning electron microscopy. The films showed increased crystallinity with stretching at temperature up to 80C. The optimum conditions to achieve beta-phase have been discussed in detail. The fabricated PVDF sensors have been tested for free vibration and impact on plate structure, and its response is compared with conventional piezoelectric wafer type sensor. The resonant and antiresonant peaks in the frequency response of PVDF sensor match well with that of lead zirconate titanate wafer sensors. Effective piezoelectric properties and the variations in the frequency response spectra due to free vibration and impact loading conditions are reported.
Materials Science and Engineering: A, 2000
Links between macroscopical behaviour and micromechanisms of deformation (constrained amorphous shearing, crystalline lamellae slip or unfolding, micro-voiding) are studied in uniaxial tension and creep tests performed on apolar PVDF at different strain rates (tensile tests), stresses (creep tests) and temperatures. Volume changes are simultaneously measured to take into account cavitation processes. The major influence of amorphous phase shearing and its competition with cavitation are described for temperatures ranging from ambient up to 100°C. Concepts of crystallite unfolding are introduced and used to understand particularities of high temperature deformation. Unfolding processes are suggested to be responsible for the different long-term behaviour (creep kinetics and fracture).
Facile Formation of β Poly (vinylidene fluoride) Films using the Short Time Annealing Process
Background: This work reports the effect of annealing temperatures on the crystalline structure of poly(vinylidene fluoride) (PVDF) film. The solution of PVDF/DMF deposited onto a glass substrate by spin-coatedto form a film of 10µm in thickness. The film is annealed at different temperatures at 30 minutes. The crystalline structure of the films investigates using XRD and FTIR techniques while the morphology determine using SEM. It observes that the dissolution of PVDF in DMF followed by spin-coating onto a glass substrate changed, directly, from alpha to beta phase which confirm by XRD and FTIR. The analyses of SEM show the surface is rough, porous and spherulites structure. They're moderately increasing of β-phase content that is equal 47% as PVDF powder to 76% as PVDF thin film. However, subsequent annealing process enhance the formation of β-phase suggesting the importance of this step.