Mesoscopic Simulation And Experimental Study On Melt Electrospinning Process In The Changing Electric Fields

Melt electrospun fibers are solventless and surface smooth, they have great application potential in biological and other high safety requirement fields, such as medical, but the fiber product has the disadvantage of the larger diameter which impedes the further development of melt electrospinning. The movement of the molecular chain in the process of jetting process plays a key role in the properties of the final product, while its control theory is still insufficient. The electric field force is regared as the mainly tensile force during the electrospinning process which induces the motion of molecular chains and leads to the refined fiber. The microscopic and macroscopic characteristics of the jet and fibers are related to the molecular chain motion patterns closely. This text aimed at understanding the control action of the electric field to molecular chains and solving the problem of the large diameter in melt electrospinning by using the changing electric field. In this paper, by considering theory and research of the decentralized force played on polymer jet and molecular chain, which called the "tug of war effect" and the vibration force field which can reduce interaction between molecules in polymer melt, the changing electric field was used to replace the original general static electric field to form the vibration force field in polymer jet and control the movement of molecular chains and obtain fibers with smaller diameter and better properties. The mesoscopic simulation method DPD and dynamic electrode plate experiment were used to study the electrospinning process and the product properties. Different kind of changing electric fields were discussed. The main works are as following:1, The absolute sine wave electric field (ASWEF) was introduced by using C++ programming language in the melt electrospinning dissipative particle dynamics (DPD) simulation system, and it was used as the main electric field for melt electrospinning process. The statistical and VMD comparison of the stretched length of molecular chain, jet diameter and jet velocity showed that the ASWEF promoted the movement of molecular chains, chould effectively reduce the jet diameter; when the control frequency is small, the effect is obvious.2, The periodic square-wave electric field melt electrospinning was studied by using the DPD simulation method. And it was found that the influence of the period on the molecular chain stretching and the jet diameter was not obvious. However, the molecular chain stretching and jet diameter is positively related to wave width. Then a pulse electric field experiment about wave width and the fiber diameter was conducted, and the results were concordant with the simulation.3, The dynamic electrode plate experiment was carried out to prepare PP fibers. Results showed that the "Taylor cone" changes dynamically. The SEM and WAXD test results showed, when the dynamic electrode moves with greater speed, the smaller the diameter of the fiber was obtained and the crystallinity increased, but the crystallization type is not affected. In addition, the orientation of the molecular chains was tested by Polarized FT-IR, a better overall orientation of the molecular chains was obtained when the speed of dynamic electrode is larger.