Effect Of Microcosmic Kinetic Parameters On Fiber Morphology In Wet Spinning Process

Improvement of quality of synthesis fiber is the main goal in producing high performance fiber. Wet spinning process is the general method for making polymeric fiber, while factors remain unknown which affect the ultimate fiber morphologies. In this dissertation, computer simulation method was earried out to study the thermodynamics and dynamics of phase separation in order to achieve the high performance product.In essential, the wet spinning process was the phase separation of a ternary system containing a non-solvent, a solvent and a polymer. In Chapter 3, a Monte Carlo diffusion model in which non-solvent, solvent, and polymer segments move on the eight nearest neighbor lattice sites was utilized to simulate the phase separation of the ternary system. A serial of different binary interaction parameters were applied in the Monte Carlo model to study systematically the various factors controlling the polymer structure during coagulation, and the representative data showed that when polymer/solvent interationχ23=0.0, polymer/non-solvent interationχ13=1.8, with varieχ12, the model obtained different skin structures ranging from sponge -like, to finger-like, then to dust-like morphologies.By varying mutalkinetic parameters we also obtain representative fiber structures metioned above. At a given coagulant penetration rate, if the mobility of polymer is high enough in the solution, polymers can coagulate into the polymer rich phase, a dense structure tends to form; on the contrary lower polymer mobility renders a porous structure usually with macrovoids. It is important in that both factors of polymer mobility or coagulant immersion act together to affect the final fiber structure, not either of them play a decisive role as was thought before. Based on the systematical simulation experiments we propose a possible mechanism that addresses how the competition between nonsolvent penetration in spinning solution and polymer segment coagulation into polymer rich domain determines the ultimate fiber skin morphologies. We believe our results are helpful in parameter selecting when producing macro void-free fiber filament and can be applied to membrane formation system as well.In Chapter 4 a three-dementional Monte Carlo simulation method with accordant model and parameters was adopted, and the result was in agreement with two-dementional simulation. It means two-dementional simulation in Chapter 3 was accurate method and saved computational cost effectively. Also the three dementional Monte Carlo programs can be applied to other polymer/solvent/nonsolvent systems.