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Research On Orientation And Crystallization Of Para-aramid In The Process

Posted on:2017-09-03Degree:MasterType:Thesis
Country:ChinaCandidate:Y Z LiFull Text:PDF
GTID:2311330503953949Subject:Material and intelligent systems
Abstract/Summary:PDF Full Text Request
Poly-p-phenylene terephthalamide(PPTA) fiber is a kind of high performance aramid fibers and which are widely used in the aerospace, national defense, composite materials. PPTA fiber is produced by dry-wet liquid crystal spinning process. The process primarily includes spinning serous preparation, the air gap tension, coagulation bath curing and heat treatment. The formation of liquid crystal in spinning serous is in the stage of PPTA dissolution and the structure of crystal and orientation in nascent fiber is obtained in the stage of solidification in coagulation bath. Therefore, in order to study the changes of crystal and orientation structure in the production of PPTA fiber, in this paper, the preparation of spinning serous and the solidification process in coagulation bath were studied.by the combination of Monte Carlo simulation and experiments.Firstly, Dynamic Monte Carlo simulation was used to study the motion law of molecular chain in the solidification process under different coagulating bath. We observed the motion law of molecular chain directly with the using of computer simulation techniques, Results showed that the macromolecular chains were pushed to center region by poor solvents in the process of solidification, forming skin-core structure. Thus, the understanding of the motion law of molecular chain is more comprehensively.After acquiring the motion law of molecular chains, the paper studied the influence of temperature on the phase structure transformation of PPTA-H2SO4 solution. POM, XRD, FTIR were used to in-situ study the increasing and decreating temperature course. The paper not only found the phase transformation temperature of 15.6% solution system, but also foud that the crystal structure in PPTA-H2SO4 solution would be destroyed when the system transformed into isotropic phase with the high temperature. The phase transformation temperature of solution system would be lower and continuous liquid crystal domain would not be formed in the decreasing process. In addition, we observed the generation procedure of orientation of PPTA-H2SO4 solution flowing in the glass capillary.In this paper, the effect of temperature and concentration of coagulation bath on curing molding is also studied. In different coagulation bath conditions, the diffusion rate in spinning serous of the poor solvent is observed with POM. The effect of coagulation bath conditions on the surface morphology of PPTA film is observed with SEM. The effect of coagulation bath conditions on the crystalline of PPTA film is observed with XRD. The results show that spinning serous could acquire better compactness and crystalline in the coagulation bath conditions of lower temperature and lower acidity.Finally, the paper combined the motion law of molecular chain observed with Dynamic Monte Carlo simulation and experimental results. The motion law of molecular chain could explain experimental results on the micro level. In return, the experimental results verify the Dynamic Monte Carlo simulation.
Keywords/Search Tags:Monte Carlo simulation, crystallization and orientation, PPTA-H2SO4 solution, coagulation bath
PDF Full Text Request
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