Processing And Properties Of Electrospun PVDF Fiber Mats

Poly (vinylidene fluoride)(PVDF) have high dielectric constant, good thermal stability,chemical durability, radiation resistance, ferroelectric and piezoelectric properties. So PVDFfilms are widely used in battery separator, piezoelectric film, filtration membranes, sensors,tissue engineering and other fields. Electrospinning is a simple and versatile method forproducing micro-and nano-scaled fibers with extremely long length.In this paper, we studied different electrospinning parameters on process of electrospunPVDF membranes, and analyzed the formation mechanism of nano-fiber/netting(NFN). Afterimproving receiving device, we explored the relationship of fiber diameter, orientation,crystallinity, additives, heat treatment and mechanical properties. And also, we researcheddifferent factors on the electrical properties of the fiber membrane.With increasing molecular weight of polymer and concentration of the PVDF solution,the viscosity of the solution increases, the conductivity decreases, but electrospinning processbecame worse. Adding ion liquid made the conductivity of solution increase rapidly, whichimproved the electrospinning processing and formation of second-scaled nano fibers named"nano spider web". And we found that when electrospinning voltage and molecular weight ofpolymer increased, it favored the formation of the "nano spider web" structure. However, withincreasing concentration of the PVDF solution, the number of nano-spider web increased andthen decreased.In the early period of electrospinning, it tended to better fiber orientation. With thespinning time increasing, the degree of orientation deteriorates. Within a certain range, thespeed of the roller became greater, and then the degree of orientation became better, but thediameter reduced. Meanwhile, orientation structure, heat treatment, high-voltage nets, and theionic liquid improved the mechanical properties of the PVDF fiber membranes.PVDF raw material has, β, γ-type crystal form. The β-type form of electrospun PVDFmembranes has little relationship with the speed of the roller. However, when ionic liquid wasadded, morphology of PVDF membranes changed significantly, the β-type crystal formbecame the main crystalline, and the degree of crystallinity slightly elevated with increasingionic liquid content. Electrospinning voltage and contention of the solution were the main factors of residualcharge of electrospun membranes. The residual charge increased with the increasing thicknessof electrospun membranes. After liquid ion was added into the solution, residual charge ofelectrospun PVDF membranes was not detected. In the piezoelectricity experiment, withincreasing impact and collection frequency, its output potential was higher. Meanwhile, theoutput voltage increases with the thickness, and then decreased.