Study On The Mechanism Of Fiber Formation For Centrifugal Spinning

This paper mainly contains two parts: one is to observe the actual jet path and build theflow field of polymer solution, the other is to establish the fiber spinnability model based onthe experiment.In chapter1the background of topic selection of this thesis is described. Everycomponents of the spinning system is discussed and the spinning head can be classified asnozzle-and nozzle-less spinnerets. The mechanism of spin-coating that relates to nozzle-lesscentrifugal spinning is discussed, and the mechanism of jet drawing and spinning parametersimpacting on the fiber formation is introduced. Then a scientific problem is proposed.In chapter2the mechanism of polymer solution flowing in the spinneret is analyzed. Wesuccessfully capture the moment of PVP solution extruding from the spinneret, and theprocess of PVP solution flowing and splitting on the rotating disk by the self-made machine.The critical angular velocity and initial jet velocity for nozzle-/nozzle-less centrifugal spinningare compared and discussed which based on the actual moment of the flow. The results showthat the critical angular velocity for nozzle-less centrifugal spinning is smaller than the nozzle-centrifugal spinning in the same spinning conditions, so polymer solution with higherviscosity can be more easily made by the nozzle-less centrifugal spinning; the relation ofinitial jet velocity, rotational speed and polymer concentration can efficiently predict theregime of rotational speed, which reduces the spinning workload. In addition, the calculationof fingers indicates that concentration and rotational speed play the opposite way to control thefinger morphology and finger velocity. It also can be inferred that the thinner and longerfingers can be obtained in a lower concentration and higher rotational speed.Chapter3analyzes the mechanism of jet drawing after the jet leaves from the spinneret.After capturing the images of jet moving, it can be found that both the nozzle-and nozzle-lessjets undergo the necking and whipping processes; the radius of2D spiral jet path jets largerwith distance but the accelerate becomes smaller, which is completely different from theelectrospun-jet that easily occurs bending instability and jet splitting. Then we compare the nozzle-and nozzle-less jet path in different rotational speeds and polymer concentrations,which indicates that increasing the rotational speed favors the formation of larger jet path butsolution concentration has little effect on the path; the path radius of nozzle-spinneret is largerthan that of nozzle-less spinneret in the same conditions.Based on chapter3, chapter4further discusses the mechanism of polymer viscosityacting on fiber morphology and diameters, and then builds the spinnability model forcentrifugally-spun fibers. We find that the beads-on-a-string structure is the mainly factor thatinfluences fiber quality through a larger deal of experiments. Therefore, we first build the jetfluctuation model which indicates that jet radius, surface tension and viscosity will influencethe fluctuation but adjusting the viscosity is the most feasible method to control the jetfluctuation. It is found that fluctuation occurs as the jet travels a longer distance in a higherconcentration and the fluctuation will disappear as a certain concentration is reached. Thereare four spinning regimes, that is, dilute regime, semi-dilute unentangled regime, semi-diluteentangled regime and concentrated regime based on the PVP and PEO spinning experimentand macromolecular-entangled theory. Eventually it can be inferred that the concentration ofcentrifugally-spun solution is much higher than that of electrospun solution.In conclusion, it is now possible to predict the jet path, fiber diameters and morphologyas the rotating jet model and fiber spinnability model is built.