Dissertation > Industrial Technology > Chemical Industry > The chemical fiber industry > General issues > Basic theory

The Research on the Ultra High Molecular Polyacrylonitrile and Other Polymer by Precipitation Polymerization and the Spinning Process of PAN

Author DaiYongQiang
Tutor JinRiGuang
School Beijing University of Chemical Technology
Course Materials Science and Engineering
Keywords High molecular weight polyacrylonitrile Precursor Kinetics Sub-cluster statistical theory Particle morphology Rheological behavior
CLC TQ340.1
Type PhD thesis
Year 2013
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PAN fiber is one of the most commonly used precursors for makingcarbon fibers. Since carbon fibers generally have the inherentcombination of high strength, high stiffness, light weight, and chemicalstability, they are uniquely qualified for use in the aerospace industry.The Properties of carbon fibers are directly influenced by thequality of PAN precursor fibers. The type of the copolymers,molecularweight of PAN, the stereoregularity and spinning methods arethe mian factors influence the performance of PAN fibers. It is aneffective way using high molecular weight polymer to enhance thestrength of PAN precursor fibers.We have done a lot of work on synthesis of high molecular weightpolyacrylonitrile and making PAN fibers with wet-spinning. This paperstudies the mechanism of mixed solvent radical polymerization of PAN.We have studied the relationships between molecular weight, conversionrate, precipitation particle morphology and the content of water in thereaction system. We got the PAN precursor with the strength is1GPa by using high molecular weight polyacrylonitrile resin. The rheologicalproperty of high molecular weight PAN spinning solution was studied byusing falling ball method. The main work we have done are as follows:1. We got the high molecular weight PAN by using mixed solventradical polymerization. The precipitation polymerization of acrylonitrile(AN) was carried out in a mixture solvent of dimethyl sulfoxide (DMSO)and water at50-65℃. We studied the effect of water content from0to90%(w/w) on the conversion of aggregation in the precipitationpolymerization. The mechanism of mixed solvent radical polymerizationwas also studied.2. The morphologies of PAN precipitates of were investigated bySEM analysis measurement. The solvent content of DMSO have greatimpact on the morphology of precipitation particle. According tosub-cluster statistical theory, we stduied the relationship of precipitationparticle morphology with the content of water and the reactiontemperature.3. We synthesis PAN by mixed solvent radical polymerization, thewater content affects the polymerization a lot. When the water content islow the polymerization tends to the solution polymerization, and whenwater content is high it tends to precipitation polymerization. Thecontribution of molecular weight of the PAN is from two parts, one isthe contribution of solution polymerization which we called the contribution of liquid phase. The other is the particle surface andprecipitation polymerization gap contributions which we called thecontribution of solid phase. Though the kinetic equation of two phasepolymerization which we metioned above, we get the expressionmolecular weight distribution of two-phase polymerizations fL(X)(theexpression molecular weight distribution of the liquid phase) and fS(X)(the expression molecular weight distribution of the solid phase). Thenwe deduce the expression of the number average molecular weight. Weobtain the values of R which is the ratio of liquid-solid phasecontributions from the data of the number molecular weight. The valueof of R show that the soild-phase polymerization play the main role forthe contribution of the number molecular weight with the increase ofwater in the reaction system.4. The purpose of this study is experimental and theoreticalinvestigations of PAN molecular weight increase in precipitationpolymerization as functions of H2O/DMSO ratio and intrinsic viscosity.To obtain the purpose, precipitation polymerization of acrylonitrile wascarried outby changing the solvent ratio of H2O/DMSO at differenttemperature, molecular weight and intrinsic viscosity ofthe obtainedpolymer were measured in DMF solution, and model mechanism ofprecipitation polymerization was suggested in relation betweenmolecular weight increases of PAN and H2O/DMSO ratio. 5. By using scanning electron microscopy (SEM) and electric singlefiber strength tester, effects of different spinning processes, especiallypressured stream drawing, were investigated on the mechanicalproperties and morphologies of precursor in the preparation of PANprecursor. The empirical relationship between fiber strength and drawratio was studied by using the sub-cluster statistical theory, with whichthe corresponding draw ratio of higher-strength precursor wassuccessfully predicted. The results indicated that: the property ofPAN-based precursor is closely related with the quality of spinning dropand spinning process. During the pressured-stream drawing, as theincrease of draw ratio, fiber diameter decreased, the degree oforientation raised, the surface of precursor became smoother and thestrength and tensile power increased. Polymerization temperaturecontrolled by stage and the results of drying collapse play a importantrole in the improvement of mechanical property of the precursor.According to sub-cluster statistical theory, it was predicted successfullywhen fiber strength was1.0GPa under a certain experimental conditionof the fiber were11.16.6. The high molecular weight PAN is difficut to dissolve, and theviscosity of the spinning solution which produced by the high molecularweight PAN and DMSO is high. The rheological behavior ofPAN/DMSO solution was studied with falling ball rheometer. We studied the relationship between the shear rate, water content,temperature, concentration and viscosity of the spinning solution.According to Arrhenius equation, the viscous flow activation energydecrease with the inerease the concentration of the water in the spinningsolution from0-3wt%. We got the PAN precursor with the diameter lessthan10μm and the intensity more than1Gpa.

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