Studies On Spinning Formation Process Of Polycarbosilan Fibers

Continuous SiC fiber with high tensile and high modulus can be produced by polymer precursor-derived method, which usually involves synthesis of polycarbosilan( PCS), melt-spinning, air-curing and pyrolysis. The spinning formation process is a basic aspect of this method and the study of the spinning formation process is valuable to promote the quality of SiC fiber and the efficiency of the method. In this paper, attention was paid to the forming process of PCS fiber. The relation was studied between the property and spinnability of PCS using GPC and IR. The curves of viscosity-temperature were drawn by testing the rheological property of PCS spinning melt. The spinning kinematics in the forming process was analysed and accordingly the distributions of diameter, velocity grads and solidifying region were obtained along spinning line. While, the variation of the microcosmic structure of PCS fiber was investigated in this process, and the influence on stability of PCS fiber forming process was discussed from the aspect of media temperature, spinning line, air current.It was found that Ta (the incipient fusion temperature) and â–³t_ab (the fusion temperature range) of PCS correlate with molecular weight, molecular distribution, branching degree and spinnability. With the molecular weight increasing, Ta is increasing; with the molecular weight distribution widening, â–³t_ab is extending, and the branching degree increasing, the spinnability decreasing. The optimum spinningparameters of PCS melt are following: 190℃ab <15℃, M_W / M_n <2.5 and A_Si-CH2/A_Si-CH3<1.2. The melting PCS is shear stress diluting fluid and its flow index is about 0.6⁰.9, its viscous activation energy is about 190²30kJ/mol. The spinnability is all right as the apparent viscosity is about 20PaS.It was the first time that the spinning kinematics was studied in the PCS fiber forming process. The results show that PCS fibers solidify at 15²0mm on spinning line. The solidifying region of PCS fiber is very short(l²0mm), about only 1/75—1/25 that of general chemical fiber. Increasing the spinning temperature and take-up velocity, the solidifying region is becoming broad. It was found that PCS fibers are amorphous, which have not crystal orientation but have feeble large molecule orientation because of the effect of stretching flow.In order to improve the formation stability of PCS fiber ,some measures can be used, such as improving media temperature, using round gas spile device and choosing spinning line length of about 90cm.