Study On Reological Behaviors Of The Dope Of Gel Spinning Of PAN Caron Fibre Precursor

Due to its a series of high performance,such as high strength,high modulus,heat-resistant,erosion-resistant etc.,carbon fiber(CF) is an advanced material used widely in all kinds of fields.However,there are large gaps in the properties and production of polyacrylonitrile(PAN)-based carbon fiber by domestic and foreign countries.PAN precursors have been the key factor for producing carbon fibers.From the viewpoint of reology,PAN solution is a non-newton viscal-elastical liquid.This is the reflection of its own structure,also it's the interior cause of reological behavior during molding.Studying the reological behavior of the dope and its effect is the way to realize the structure of the dope and its transformation rules.The filature stability, homogeneity and the best technics conditions of PAN solution have close correlation with reological behavior of the dope.In the dissertation,the content and the kind of non-solvent additive(NSA) were investigated.The orientation of the dope and its maintenance,the homogeneity and stability,the effect of the temperature of gelation,the best technics conditions were also investigated.The main results obtained are as follows: During steady shear flow measurement,the trend of the reological curves was not influenced by different NSA at different temperatures. Whether H₂O or ethanol were added into the dope or not,at lower shearing velocity the reological curves went downwards with the increase of temperature and the reological vurves went downwards first then went upwards with the increase of the content of NSA.At higher shearing velocity,the reological curves almost overlapped.The upwards of the reological vurves were not obvious with the increase of the temperature. H₂O is a more effective NSA,the solution containing H₂O can gel more easily.PAN/DMSO/H₂O solution maintained the oritaintion well when it was sheared and went through relaxation for a short time.It was good for improving the degree of oritaintion.The viscous-elastic modulus of PAN/DMSO/H₂O solutions increased with the decrease of temperature or with the increase of the nonsolvent content.For the same tested sample,the state and homogeneity changed at different temperatures,this phenomena had close correlation with the gelation of the dope.For the samples with different content of NSA,the homogeneity of the dope was different.To improve the quality of the PAN-based carbon fiber precursor,avoiding composition induced gelation was absolutely necessarily.The pore size and number of the section of the PAN-based carbon fiber precursor increase with the increase of the gelation temperature.When the quenching temperature was-5℃,the structure of the PAN-based carbon fiber precursor was homogeneous as the fiber gelled quickly within short time.PAN solutions showed shear thinning viewed from the reological curves.The solution was non-newton liquid.The non-newton reological behavior was more obvious with the increase of the temperature or the increase of the content of PAN.The result was accordant with non-newton index n.As the the elasticity of the dope was small,it almost had no influence on the non-newton reological behavior.The non-newton reological behavior was likely induced by the cumulation of the strain.During the experiment above,it was indicated that:for the dope of PAN 20wt%,the better technics parameter were:the temperature of the dope was 70℃;the content of NSA was 5%-6%;the temperature of the first freezing bath was the lower the better.