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Effect of Air Gap on Morphology of Polyacrylonitrile Triangular Fiber

Polyacrylonitrile triangular fiber was prepared by the technique of dry-jet wet spinning. In order to study the effect of air gap on the morphology of triangular nascent fiber, various air gap distances ranging from 3 to 7 mm were studied. The cross-section of triangular nascent fiber was observed through an optical microscope, the surface of the fiber was examined with an atomic force microscopy, and its pore structure by mercury porosimetry. The results showed that the profile degree decreased with the increase of air gap distance; the surface tension was a key factor that affected the deformation of the cross-sectional shape of triangular nascent fiber. In addition, surface roughness of triangular nascent fiber, with the growth of air gap distances, increased first and then decreased. An abrupt change of the surface roughness of the fiber may have resulted from that of polymer contents on the surface of the dope stream in the air gap. Furthermore, the pore volume in the triangular nascent fiber decreased with the increase of air gap distance. This may be attributed to change of the total polymer content of the dope stream in air gap.