Study Of Melt-Electrospun PET Fiber Formation And Film Structure

In this paper, the distribution of electric field of our melt-electrospinning setup was simulated by ANSYS software with the finite element method (FEM); the influences the main parameters (including spinning voltage, accepted distance and collector area) in straight-melt-electrospinning and reverse-melt-electrospinning process had on electric field distribution were investigated respectively. Then the experiment of melt-electrospinning with polyethylene terephthalate(PET) was conducted to study the effects the electric field distribution had on the fiber formation, fiber morphologies and fiber film self-assembly structures. The controllable formation of fiber film by melt-electrospinning was realized.The results of simulation of electric field shows that, the potential distribution in straight-melt-electrospinning and reverse-melt-electrospinning process are reverse. For straight-melt-electrospinning and reverse-melt-electrospinning process, although the influences’trend each parameter had on electric field are similar, since the charged jet deposition in the spinning experiments, there are great differences in the fiber formation and film structure between these two processes.In straight-melt-electrospinning process, the electric potential decreases from nozzle to collector. In the single nozzle-plate structure model, electric field distribution was uneven; in the vertical direction, the strong electric field is mainly concentrated on the nozzle and changes exponentially with distance, while linearly change in the zone away from the nozzle; in the horizontal direction of collector, electric field strength decreases from center to edge.In spinning process, the jet whips obviously and deposits a hat-shaped fiber films due to uneven electric field. In addition, the periodically changing electric field by depositing charged jets makes the jet move forth and back from center to edge, forming a self-layering structure in fiber film.When improving voltage, the whole space electric field intensities becomes enhanced and the force the electric filed on jet becomes large, making jet whipping radius smaller while the whipping angle larger and the fiber average diameter smaller. Besides, the bottom radius of film decreases, the fiber film becomes thick, and the bulging effect in the center of film is enhanced. In addition, the layering structure is apparent and the number of layers becomes larger with increase of the voltage.The changes of accepted distance apparently affects the electric field on the collector surface. Increasing accepted distance would decrease the jet straight segment proportion while increase the whipping radius, and the fiber shows a small diameter with a moderate accepted distance. Besides, increasing accepted distance can flatten the fiber film almost eliminating the bulging center of film; the self-layers of film shows a little change while there is few binding-fibers between the layers. Decreasing the collector area could modify the evenness of the electric field between nozzle and collector by enhancing the electric field and more control on jet motion, making jet straight segment proportion larger and whipping radius smaller; depositing angle becomes smaller with the jet closed to collector; while fiber diameter increases slightly. Besides, the bulging effect becomes more obvious, the center thickness of film increases twice in the case of larger collector area, and the bottom radius decreases slightly while the layers is increasing.In the reverse-melt- electrospinning process, the influences trends spinning voltage, accepted distance and collector area had on electric field of reverse-melt- electrospinning is similar to that of straight-melt-electrospinning, but the real electric field is really different. While the electric potential increases from nozzle to collector until set spinning voltage. The charges on deposited jets could be transferred quickly and even the polymer is broken down by high voltage which makes the potential difference smaller between collector and deposited fiber film, so the jet moves closely to the film and prepared 3-D core-shaped fluffy films without layering structure. When improving voltage intensifying electric field, the whipping angle decreases until the jet moves much closer to the surface of the cone-shaped fiber film; the average fiber diameter is becoming smaller; increasing the voltage will also increase the feeding speed, so the sizes (bottom area, thickness and mass) of 3-D melt-electrospun PET fiber films get increased, while the core angles of films decreases greatly due to the unevenness of electric field. With smaller accepted distance, the PET jet is with a greater straight segment proportion, the end of jet touches the top of the film directly and the jet whipping section shapes with a bulging arc-segment; when increasing accepted distance, the gap between the end of jet and the top of the film becomes larger, the jet whips linearly with a smaller whipping angle; fiber diameters are with few changes when changing the accepted distance; increasing accepted distance would decrease the films’ sizes and weight, also the core angle decrease greatly. Decreasing the collector area, the fiber jet end is much closer to the film top and its bulging arc-segment becomes more obvious; the fiber diameters decrease slightly; and the films’ sizes increases while core angles decreases.