The Research Of Rheological Behavior Of Ultra High Molecular Weight Polyacrylonitrile Dope

Carbon fiber has a series of high performance, such as high strength, high modulus, heat-resistant, erosion-resistant, etc. At present, carbon fiber is widely used in all kinds of fields. PAN fiber is one of the most suitable and widely used precursors for fabricating high performance carbon fiber. However, the polyarcylonitrile dope obtained in China now is not only poor at tensile property, but also has a lot of fuzz. This requires that we strengthen the investigation of PAN solution and precursor and lay a solid foundation for domestic high-performance carbon fibers.A brief introduction of properties of PAN solution and the models of elongational flow and shell flow is given in this thesis. This work is focused on the elongational and shell tests of polyacrylonitrile dope which is added the ultra high molecular weight polyacrylonitrile. The main results and conclusions are as follows:First, we use a new method called'Capillary Breakup Extensional Rheology'(CaBER) to study the elongational properties of polyacrylonitrile solution for the first time. We find that the samples with ultra high molecular weight polyacrylonitrile show strongly strain hardening in the tests. Molecular weight and the contents of the ultra high molecular weight polyacrylonitrile in the samples all affect the elongational properties:with the increase of the molecular weight or the contents of the ultra high molecular weight, the steady-state crisis elongational viscosity, Trouton ratio and elongational viscosity all increase.Then we test the shell properties. The ultra high molecular weight polyacrylonitrile exhibits shear thinning behaviors. Temperature, molecular weight and the contents of the ultra high molecular weight polyacrylonitrile all have effects on the shell properties of the samples. The temperature increases, and the dope with a low content of ultra high molecular weight polyacrylonitrile has a trend to be Newton fluid. Solution with a high content doesn't show such respond. At a low temperature, RG, the ratio of the high-shell-frequency storage modulus and low-shell-frequency storage modulus, is a constant. The temperature increasing, RG is increasing. With the increase of the molecular weight, Ra, the ratio of the high-shell-rate viscosity and low-shell-rat viscosity decreases but RG, the shell viscosity, storage modulus and loss modulus all increase. With the increase of the content of ultra high molecular weight polyacrylonitrile, the shell viscosity, RG, storage modulus and loss modulus all increase but Ra tends to be a constant. We also find that the Trouton ratio and the non-Newtonian index all demonstrate the similarity of the level of the samples deviating from the Newton fluid. The deviation develops with the increase of molecular weight and the contents of the ultra high molecular weight polyacrylonitrile. The evaluation of PAN solution parameters provides a theoretical guidance for the preset value of relevant parameters which make spinning stable.