Facile synthesis of ZnO particles and the effect of their usage as fillers on the 𝛽 phase content and mechanical properties of PVDF and PVDF-HFP polymers

Abstract

Polyvinylidene fluoride (PVDF) and its co-polymers are widely used, especially in wearable devices, because of their flexibility, high mechanical strength, high chemical resistivity, and biocompatibility. They are also easily processable and are of relatively low cost. The 𝛽 phase of PVDF and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) present outstanding electrical characteristics including piezo, pyro and ferroelectric properties. Zinc oxide (ZnO) nanoparticles are often used as fillers to induce the 𝛽 phase of these polymers. In using these fillers, it is also important to be concerned about their effect on the mechanical strength and flexibility of the polymers. This research focuses on facile low-cost synthesis of ZnO particles, and the incorporation of these particles into PVDF and PVDF-HFP polymers to determine how the size and shape of the ZnO particles affect the 𝛽 phase percentage, strength and flexibility of the above-mentioned polymers. The ZnO synthesis was carried out by the chemical precipitation method using low-cost chemicals, followed separately by microwave irradiation, and thermal decomposition. The sizes and the morphologies of the synthesized samples were assessed using scanning electron microscopy (SEM), and particle size was measured using Image J software. The microwave irradiation synthesis method gave ZnO rods with a mean width of ~177 nm. ZnO granules, synthesized using the thermal decomposition method, using Na2CO3 as the base, gave particles with a mean size of ~75 nm. X-ray diffraction (XRD) was carried out to confirm that the samples synthesized were wurzite ZnO. The preparation of the polymer and polymer/ZnO composite films was carried out using the solvent casting method. Fourier-transform infrared spectroscopy (FTIR) was carried out on the samples with the dual intention of identifying the sample and comparing the effect of the ZnO nanofillers on the 𝛽 phase content of the polymers. The highest percentage increase in 𝛽 fraction, of ~48% over the pure polymer sample, was shown for the Polymer/ZnO composite sample of PVDF/ZnO granules. Mechanical testing was carried out in order to compare Young’s moduli and the tensile strengths of the samples. The highest tensile strength, of ~ 9.2 × 105 𝑁 𝑚-1, among the ZnO/polymer composites, was observed for the PVDF-HFP/ZnO rods sample. The lowest Young’s moduli of ~ 8.8 × 107 𝑁 𝑚-1 , and hence higher flexibility was observed for the PVDF/commercial ZnO.