Effects Of UHMWPAN On The Spinability Of MMWPAN/DMSO Spinning Dope And The Properties Of Precursor

With a series of performances,such as high strength,high module,heat resistance,corrosion resistance,heat conduction and small coefficient of thermal expansion,carbon fiber becomes a kind of idealist functional and constructional material.PAN-based carbon fiber is the most widely used and promising carbon fiber.The quality of PAN precursor fiber determines the performance of PAN-based carbon fiber to a large extent.The domestic PAN-based carbon fibers are generally at low quality level compared with those produced by some developed countries,which is mostly due to the low quality of domestic PAN precursor.In this dissertation,ultra high molecular PAN(UHMWPAN)and medium molecular PAN(MMWPAN)have been blended into DMSO solution.The spinnability of solutions with different composition have been investigated to explore the best spinning condition and make high quality PAN precursor.The structure and performance of PAN precursor have also been studied.In the steady shear rheology test,the temperature dependency of viscosity has been discussed.By fitting viscosity-shear rate curves,the zero shear viscosity can be calculated.The temperature dependence of viscosity is described by free activation energy which is calculated through the Arrhenius equation.The value of free activation energy shows that the solution with high molecular weight or concentration is more sensitive to temperature.The apparent viscosity under the same concentration of UHMWPAN/DMSO solution is much higher compared to the solution without UHMWPAN and the calculated non-Newtonian index shows that as the content of UHMWPAN increases,the solution is getting closer to typical non-Newtonian fluid.In the dynamic shear rheology test,both storage modulus G’ value and loss modulus G" value increase with the increase of UHMWPAN content.The former is slightly faster.In the elongation rhology test,the way of diameter getting thinner is affected by molecular weight.If the molecular weight is too small,liquid filament will be broken immediately;but,when the molecular weight is high enough the liquid filament can be kept a while.UHMWPAN can extend the break time of liquid filament.But it will swing to the opposite if the content of UHMWPAN is too high;the best Mu/Mm value is 0.5%.Elongation viscosity increases with the increasing molecular and PAN content and deceases with the increaseing Hencky strain rate.All of the solution of which PAN content are 21%shows strain hardening,UHMWPAN can strengthen strain hardening.The elongation viscosity curve of high UHMWPAN content solution has some oscillations which may reduce the stability of the stretching process.In addition,the Tr value becomes larger with the increasing UHMWPAN content,which means the solution deviate Newtonian fluid.In the dry-jet wet spinning process,the spinnability gets better when UHMWPAN was added in the solution.The best spinning temperature is 70-80 ℃,higher than the solution without UHMWPAN.The best air height is 30-50mm.The cross section of filament with UHMWPAN is closer to circular and the surface is smoother,compared to the filament without UHMWPAN.With the increasing Mu/Mm value,the crystallinity increases at first and then decreases,0.5%is the turning point;the degree of orientation decreases at first and then increases,0.7%is the turning point.The elongation at break improves as tensile strength decrease.