The Effects Of Spinning Condition On The Structure Of Mesophase Pitch Fiber And The Research Of Stabilization Of The Fiber

Mesophase pitch carbon fiber has been widespread investigated for a long time as strategicmaterials, due to a series of excellent performance, such as high strength, high modulus, highthermal conductivity, low coefficient of thermal expansion and so on. Mesophase pitch fiber isobtained through melt spinning, because the composition of mesophase pitch is too complicated tobe dissolved completely for wet spinning. The characteristics of mesophase pitch fibers preparedby mesophase pitch spinning differ much from other polymer fibers, owing to its low molecularweight, usually around500-3000.Therefore, the experience or theory in polymer fibers aspects cannot be used to guide the mesophase pitch fiber study.Preparing high performance mesophase pitch carbon fiber requires the diameter of fiber getsas small as possible, which can be done by increasing drawing ratio in the stage of spinning.Butunlike polymer fiber drawing, large drawing ratio can reduce fiber diameter but can’t improve thefiber orientation along the axial direction. In this paper, the influence of drawing on the orientationwas studied after adding cooling device under the spinneret plate.This paper also studied thepre-oxidation behavior of mesophase pitch fiber to demonstrate the structure change.It was foundthat: when the slow cooling temperature was lower than the softening point of220℃, an increasein the slow cooling temperature could improve the degree of orientation of pitch fiber. Theorientation degree increased by0.34%、0.85%and0.13%respectively under the draw ratio of30.45,57.74and71.04. The orientation degree of pitch fiber first decreased and then increase at the slow cooling temperature at220℃. At the slow cooling temperature of240℃,the orientationdegree increased from84.58%to85.59%with increasing the draw ratio from30.35to71.04. Theeffects of the slow cooling temperature and the draw ratio on the thickness of microcrystalline areaccord with the degree of orientation. The crystallite thickness is proportionate to the degree oforientation. Measuring pinch molecular layer spacing using XRD lacks precision because of X rayincident wavelength. Therefore, the relationship between the change of molecular layer spacing,orientation and crystallite thickness should not be observed.Based on the change of functional groups on the pitch fiber surface at different pre oxidationtemperature and the stress-strain curve in air and nitrogen atmosphere, it can be found that theoxidation reaction of mesophase pitch almost doesn’t occur below250℃and the extent ofoxidation reaction is still insufficient below250. It can be observed obviously that mechanicalproperty changes were caused by crosslinking and cyclization.