The jet swell effect in the wet spinning of polyacrylonitrile (PAN) fiber was studied by optical microscopy and the jet swell ratio was obtained through directly measuring the diameter of the freely extruded fibers. For reflecting the actual drawing situation of the fibers in the coagulation process, the jet stretches were then corrected from the apparent values to the true values, and their effect on the cross-sectional morphology, internal structure, and orientation of the wet-spun PAN fibers was studied by optical microscopy, scanning electron microscopy, and X-ray diffraction, respectively. The results showed that jet stretch plays an important role in eliminating the adverse effects caused by the jet swell effect and affects the fiber structure; PAN fibers of uniform denier, dense and homogenous structure, and high orientation can only be obtained at a suitable jet stretch.
Liquid hyperbranched polycarbosilane (LHBPCS) is an excellent preceramic polymer of SiC. Before thermolysis, curing of LHBPCS is favorable for higher ceramic yield and molding. In order to avoid some unfavorable factors arising from traditional thermal curing, we introduced a free‐radical initiator tert‐butyl peroxybenzoate (TBPB) to trigger the crosslinking of allyl group on LHBPCS in this study. FT‐IR, NMR and DSC measurements indicated only allyl group was consumed during the cross‐linking process. The cross‐linking reaction rate was monitored by a rotational rheometer, and results confirmed LHBPCS could be cured in 4 minutes with the help of 1 wt% TBPB at 80°C. TGA and SEM demonstrated the catalytic‐cured LHBPCS had a high ceramic yield of 79.0 wt% and dense structure. The effect of TBPB on crystallization behavior of the obtained SiC was also explored by XRD, and little impact was detected. After 1600°C thermolysis, a near stoichiometric and crystalline SiC with ceramic yield of 77.5 wt% was obtained.
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