Melt electrospinning of thermoplastic polymers
This dissertation is concerned about developing of melt electrospinning strategies of thermoplastic polymers. The goal was to generate polypropylene nanofibers from the polymer melt instead from the polymer solution. Through this method, organic, toxic or environmentally non-friendly solvents can be avoided offering a clean process for nanofibers production. Melt electrospinning necessitates the use of polymer melts with lower melt viscosity since high melt viscosities inhibit the formation of ultrafine fibers. The generation of ultra-fine polypropylene nanofibers to utilize these fibers in filter media was studied. The ultra-fine size fibers below 1 µm offer great surface area that assists us to be used as filter media. At the beginning, a simple melt electrospinning device was designed and the melt viscosity of polypropylene was influenced. The effect of the melt viscosity on the produced fiber diameter was studied. Furthermore, the effects of the ambient and the processing parameters on the electrospinning process and the resulting fiber diameter were studied. In the next chapter, the melt viscosity of polypropylene was influenced by blending of different molecular weights polypropylenes, by addition of small molecules (sodium stearate) and by increasing of the melt temperature. The aim is to recognize the melt viscosity limits which enable us to obtain ultra-fine polypropylene fibers. In the following chapter, process and ambient parameters and their effect on fiber diameter were studied. These parameters were investigated in order to optimize the conditions for generation of small fibers. Furthermore and after investigation of the effect of melt viscosity and processing parameters, the chosen polypropylene mixtures were mixed with nucleating. Three different types of nucleating agents were used to enhance the nucleation process in polypropylene electrospun fibers. The amounts of nucleating agents were altered in order to obtain the highest possible melt enthalpy (dH) that indicates the highest degree of crystallization. The effects of nucleating agents’ type and their amount on the fiber diameters and the degree of crystallization were studied.
info:eu-repo/classification/ddc/540, Elektrospinnen, Rheologie, Viskosität, Nukleierungsmittel, Chemie, electrospinning, rheology, viscosity, nuclating agents
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