Effect Of Spinning Shear Rate On PAN As-spun Fiber Structure And Its Drafting Properties

In the engineering practice of preparing PAN fiber, we found that in the wet-spinning process, with the improving of the spinning shear rate the more broken fibers happens during the drafting process. This situation leads to decreasing of the fiber's properties, fiber beam break down even worse. Under the same drawing crafts and drafting environment, the structure of the as-spun fiber, forming before the drafting process is the key to the decreasing of the drafting performance. As-spun fiber structure is the basis for the final PAN fiber structure and evolution. The importance of as-spun fiber structure has not been emphasized more in the previous study. In this thesis, the practical problem—increasing the spinning speed has been considered from a scientific point of view. The effects of shear rate on extrusion swelling effect were investigated. The method of characterization of the surface groove structure of as-spun fiber was established. The mechanism and effect of shear rate on the as-spun fiber structure during it forming process has been studied, also the regulation of it. The relationship between the as-spun fiber structure and fiber drawability has been discussed simultaneously. Rheometer,macro camera, image analysis software, scanning electron microscopy,atomic force microscopy, XRD and other test methods has been used to analyzing the extrusion swells of the PAN/DMSO concentrated solution and as-spun fiber structure, the results show that:1?In the wet spinning process, the extrusion swell happens during the PAN/DMSO spinning solution extrusion process. And it will be greater with the increasing of shear rate. The extrusion expansion ratio has a close relationship with the viscoelastic properties of the spinning fluid and the coagulation conditions, which has important influence on the forming process of the as-spun fiber.2?The carbon fiber surface trench structure is formed in the wet spinning process. Worked under the extrusion swell of the PAN/DMSO spinning solution and the solidification effect, solidification and rupture occurred several times on the surface of the spinning fluid in a short period of time, which result in the groove structure on the fiber surface.With the increasing of the shear rate, the density of the groove is increasing. The axial coagulation tension has been effected by the extrusion swell. The formation of aggregate structure of as-spun fiber is effected by changes of the force field and solidification time, causing by changes of shear rate. Increasing of spinning rate has less effect on the morphology of the nascent fiber cross-section, the pores of the cross section, roundness, average diameter almost no effect, increased diameter difference.3?With the increasing of the shear rate, the drawability of the as-spun fibers is reduced. This reduction is a macroscopic manifestation of the structural changes of the as-spun fibers caused by the shear rate.Regulation of the drawability by the characteristics of the spinning liquid and solidification conditions is also studied, and analyzed from the as-spun fiber structure.