Physico-Mechanical Properties of New Electrospun Polyvinylidene Fluoride Nanocomposites

Abstract

This study aimed to prepare and characterize poly(vinylidene fluoride) (PVDF) nanofibres with the following additives: graphene oxide (GO), cellulose, and silver nanoparticles (Ag-NPs). Two types of solvents were used to prepare the virgin and composite materials: acetone and DMF, which lead to a porous surface of the nanofibres. Effect of combination of the additives and the effect of two salts (sodium chloride and tetraethyl ammonium chloride) was also considered. These nanofibres were produced by electrospinning technique. The properties of the prepared samples were studied by scanning electron microscope, differential scanning calorimeter, Fourier transform infrared, X-ray diffraction, thermal gravimetric analyzer, tensile test instrument, dynamic mechanical analyzer, and dielectric analyzer. The objective of this study is to improve the crysallinity percentage and especially the beta phase content in the produced nanofibers which is important to improve the properties for different applications such as energy harvesting. Ag-NPs improved the smoothness and reduced the thickness of the nanofibres due to the increase in conductivity but upon increasing the concentration to more than 1.4% agglomeration occurred and polydispersed fibres are produced. Improvement of the crystallinity percentage was achieved to a maximum at the following percentage 0.3%GO, 0.5% cellulose, and 0.4% Ag-NPs with crystallinity percentage of 50%, 43.2% and 45.4% respectively, these values are higher than the 41.7% of the PVDF nanofibres. The same additives percentage increased the thermal stability of the nanofibres (with exception of cellulose which had a shift to 1% rather than 0.5%). Combination of fillers lowered the crystallinity percentage compared to single additives due to the heteronucleation effect of the fillers. Enhancement in the beta phase was achieved at the following concentrations of the additives 0.1% GO, 1% cellulose and 0.2% of Ag-NPs. The nanocomposite became less compact as the 2O shift to lower values. Improvement in storage modulus was achieved with the addition of 0.3% of GO due to the stiffness of GO sheets. The similar effect was achieved with the addition of 0.5% of cellulose and 0.2% of Ag-NPs, but due to the polymer chains are entrapped in the agglomeration of the particles, and cannot move freely. Loss modulus had a considerable low value when 0.7% of GO was added to the PVDF which showed improved mechanical energy distribution within the material. The relative permittivity of PVDF/GO, PVDF/cellulose, and PVDF/Ag-NPs is improved with addition of the fillers, it was around 50% at low frequency, this improvement could be due to the Maxwell-Wagner-Sillar (MWS) interfacial polarization.