Research On The Spinning Process Of High Molecular Weight Polyacrylonitrile-based Carbon Fiber Precursors

Carbon fibers are widely used in aerospace industry due to their inherent properties of high carbon content, high strength, high modulus, excellent mechanical properties and chemical stability. The precursor fibers of high quality are necessary to produce high-performance carbon fibers, and the polyacrylonitrile (PAN) precursor is the chief raw material for carbon fibers in recent years. The properties of the precursor fibers are the main constraints in the fiber formation process. Factors that affect the performance of precursor fibers are mainly about the comonomer type, spinning method, parameters and process conditions of the coagulation bath, thermal water and high pressure steam drawing process, degree of drying densification process, oiling technology, etc.Therefore, a plenty of work which includes the synthesis of high molecular weight PAN and the research of spinning process has been accomplished to obtain superior precursor fibers. The present experimental work is focus on the process of the precursor fibers, especially the process of the coagulation bath. In order to gain better morphology and properties, the three factors (ie, the three coagulation parameters:temperature, concentration, the negative draw ratio) have been designed by the orthogonal experiment. A variety of tows with different parameters were obtained by multiple parallel tests.The surface morphology and the cross section morphology of the spun fiber were studied using scanning electron microscopy (SEM), the crystalline grain size was detected by X-ray diffraction (XRD), and the strength of the spun fibers was tested by electronic single fiber strength testing machine. The results showed that the influence degree of the three parameters of coagulation bath to the cross section morphology of the spun fibers was:coagulation bath concentration>coagulation bath negative draw ratio>coagulation bath temperature. The influence degree to the crystallization was:coagulation bath negative draw ratio>coagulation bath concentration> coagulation bath temperature. The most excellent coagulation bath parameters were obtained, in which the coagulation bath concentration, negative draw ratio and temperature were80%,0,40℃respectively. The high molecular weight PAN fiber, which was spun with the parameters above by the wet spinning process, not only has excellent superficial morphology and circular cross section, but also possesses good surface morphology and mechanical properties.Drawing process included multi-stage coagulation bath drawing, thermal water drawing and high pressure steam drawing. The fibers with different draw ratio were studied using SEM, XRD, electron single fiber strength testing machine respectively. The results showed that when the draw ratio was5by the thermal water drawing, the PAN precursors possessed highly strength and superior property, while by the high pressure steam drawing, the draw ratio was only2.5. As a result, the excellent carbon precursor fibers with the strength over1GPa have been prepared, which optimize the experimental program and is instructive and meaningful to the further experiments.