Polycarbosilane Fibers Forming The Basis Of Research

Continuous SiC fiber with high tensile and high modulus can be produced from polycarbosilane(PCS) by the process of spinning ,curing and heat treatment. In this paper, attention was paid to the formation of PCS fiber and its affecting factor. The rheological property of PCS and influence on melt spinning were systematically studied. It was found that precipitation fractionation could regulate molecular weight distribution. The spinnability of fractionated and unfractionated PCS and characteristic of SiC fiber were investigated. The influence of molecular weight distribution of PCS on spinnability and mechanical property of SiC fiber was studied by means of IR, GPC and SEM. The influence of temperature, pressure and winding velocity on spinning of PCS was studied. It was the first time that softening point and melt index could be considered the simple standard of spinnability of PCS. The spinning kinetic of PCS was simulated, and the distribution of temperature, diameter on spinning path was obtained.We found that PCS was typical shear stress diluting fluid and its flow index was about 0.6. Its apparent viscosity depended strongly on temperature, and its viscous activation energy was about 270kJ/mol. The spinning temperature must be strictly controlled to improve spinning stability. Precipitation fractionation could narrow the molecular weight distribution of PCS and reduce high and low molecule, which may make it difficult to be spinned, but could improve the mechanical characteristic of SiC fiber. When the melt index of PCS whose softening point was 195-205 ℃ was about 36-38g, the spinnability was good; When the melt index of PCS whose softening point was 210-220℃ was about 32-34g, PCS had good spinnability. It was found that theapparent viscosity of PCS melt could be calculated: and the best spinning viscosity was 400-600 Pa - s. We found that PCS fiber had not apparent crystallization and orientation. From the kinetic simulation we knew, it was at 0.1m on spinning path that the ultimate diameter could be obtained and temperature decreased to about 50℃. So it was difficult for us to stretch PCS fiber to decrease its diameter.