Preparation And Properties Of Ultrafine Fibrous Membranes From Poly(Vinylidene Fluoride) By Electrospinning

Polyvinylidene fluoride (PVDF) were processed into fibrous membranes byelectrospinning from its solutions in the mixture of N,N-dimethylformamide (DMF)and acetone in this paper. Influencing factors were mainly discussed, includingapplied voltage, concentration of solution, flow rate, collecting distance and ratios ofdifferent components in solvents. The thermal and mechanical properties of theelectrospun PVDF membranes were examined. These electrospun PVDF fibrousmembranes would be potentially applied in electrolyte separators in Lithiumsecondary batteries. The morphology of the electrospun PVDF fibrous membranes was investigatedby scanning electron microscopy. Surface tension, viscosity and conductivity of thePVDF solutions were measured at different concentrations and different ratios ofcomponents. Their changes also had influence on the morphology of the electrospunfibers. Results showed that polymer concentration and ratios of different componentsin solvents had evident influence on the electrospinning process. With theconcentration changing from 10%-17%, the process of electrospinning became moreand more difficult because of increase of viscosity and the distribution of fibersdiameter changed from 50 nm -400 nm to 200 nm -500 nm. It is suggested thatuniform ultrafine fibrous membranes could be obtained when the concentration was15%. With the concentration increasing, the density of beads and beaded fibersdecreased and the morphology became much more orderly. The diameter showed adecrease tendency with increase of the acetone amount in the solvent mixture and thedistribution of fiber was in 40 nm -500 nm when the amount of acetone was 20% inthe solvents. There was no clear difference in morphology when the flow rate increasedfrom 0.3 mL/h to 0.5 mL/h, and the distributions of the fibers diameters both focused on the rangeof 100 nm -400 nm. When the voltage increased from 5 kV to 10 kV, there was littledifference in the morphology and the distribution of fibers diameter both focused on200 nm-400 nm. The deposition distance had little influence on the morphology offibers and the distribution of fibers diameter focused on 100 nm -300 nm. In thisexperiment, the best condition for PVDF electrospinning was that the acetone amountin the solvents was 20%, the concentration was 15%, the voltage was 5 kV, the flowrate was 0.3 mL/h and the deposition distance was 15 cm. A revolving canister connected with ground was selected as a collector, whichwas covered with aluminium foil. And the obtained membrane was about 20 μm-50μm in thickness electrospinning for 8-10 hours. A series of typical stress-strain curves iiwere obtained via a group of samples which shape was made to 70 mm×10 mm inpulling experiments. The tropism of fibers was not clear and the distributing of fiberswas disordered. With the increase of concentration, the performance of membranedecreased from 126.3 MPa and 113.0 MPa to 21.59 MPa and 24.97 MPa. The fibrousmembranes were made dry in vacuum oven and the remains in the solvents wereaccounted about 0.38%-0.66%. The crystallization was analyzed via differentialscanning calorimetric and wide angle X-ray diffraction to find their difference. Andthe crystallization of PVDF membrane enhances a little with the increase of solutionconcentration.