Study On The Jet Stretching Of Electrospinning Polyvinylalcohol(PVA) Nanofibers On The Basis Of Carbon Nanotubes And Polycaprolactone Microspheres

As a simple method to produce nanofibers, electrospinning is attracting more and more attention from the scholars. Electrospun nanofibers have higher specific surface area and larger surface-to-volume ratio, possessing a lot of pores. These advantages endow the electrospun nanofibers improved performance and wide range of applications, including composite materials, filtering membrane, sensor drug release and tissue engineering. The degree of jet stretching and refining during electrospinning determines the diameter and uniformity of nanofibers. Therefore, it is significant for controlling the diameter of nanofibers effectively to study the stretching mechanism of the jet. In this study, we analyzed the forces exert on the electrospun jet according to the mass conservation, charge conservation and momentum equation, improved the previous model by increasing the effect of surface tension and internal pressure. The relationship between stable jet diameter r and the vertical distance of jet away the Taylor vertex z was r～Cz-1/2+C1. C and C1are both constant.The electrospun nanofibers are randomly collected in the form of nonwoven with low strength, which is the major technical barrier for manufacturing electrospun fabrics for applications. In order to improve the performance of nanofibers, this paper studied the electrospinning mechanism of composite nanofibers by adding single-walled carbon nanotubes(SWCNTs) with excellent mechanical, electrical and thermal properties into PVA solution. Theory about the effect of SWCNTs on the stretching of stable jet was predicted, established the stretching model:r～z-1/2.We also analyzed the changes of the solution properties (viscosity, conductivity and surface tension) on the electrospinning. The tests showed that:with the increasing mass fraction of SWCNTs, the solution viscosity increased exponentially; the conductivity increased linearly; the surface tension was almost no change, fluctuating within a certain range. Electrospun PVA solution with different mass fraction of SWCNTs, intercepted the stable jet using a glass slide, the jet morphology was observed and the jet diameter was measured under a microscope. The relationship between stable jet diameter r and the vertical distance of jet away the interception point z wasr～z-1/2. The added SWCNTs had little influence on jet stretching rate compared to that of pure PVA solution. However, the jet diameter increased with the increasing mass fraction of SWCNTs. So the experimental results are consistent with the theoretical derivation, which verify the reasonable of prediction and feasibility of the theoretical analysis.In this paper, microspheres were produced by emulsion solvent evaporation method. Polycaprolactone (PCL) was chosen to fabricate microspheres and low viscosity PVA was emulsifier. By orthogonal testing analytical method, emulsifier PVA concentration was found to have relatively greater effect on microspheres diameter C.V. than the other parameters.The PCL microspheres were added into the high viscosity PVA solution for electrospinning. Theory about the effect of microspheres on the stretching of stable jet was predicted. This paper started from radial displacement of stable jet to derive the stretching model, combining quasi one dimensional equation of dynamic free jet with no moment, which meets:r～z-1.We also analyzed the changes of the solution properties (viscosity and conductivity) under different mass fraction of PCL microspheres. The tests showed that:with the increasing mass fraction of PCL microspheres, the viscosity increased exponentially; the conductivity reduced in a certain range. Electrospun PVA solution with different mass fraction of PCL microspheres, intercepted the stable jet using a glass slide, the jet morphology was observed and the jet diameter was measured under a microscope. The relationship between stable jet diameter r and the vertical distance of jet away the interception point z was r～z-1.The added PCL microspheres had significant influence on jet stretching rate compared to that of pure PVA solution. However, jet diameter almost had no change with the increasing mass fraction of PCL microspheres. So the experimental results was consistent with the theoretical derivation, which verify the reasonable of prediction and feasibility of the theoretical analysis.