Structure Of Dry-jet Wet Spinning PAN Nascent Fiber

Dry-jet wet spinning is an important process to prepare polyacrylonitrile(PAN) precursor, because PAN precursor from this process has better density and high mechanical performance of structure, more and more researchers pay attention to this process. PAN nascent fiber is the most original fibrous precursor of carbon fiber. Limited drawing is applied on nascent fiber in solidification process, so the fibers’ diameter is very large. In order to meet the requirements of preparing high-performance carbon fiber, we need to apply further drawing through multi-stage coagulation bath, and then get denier PAN precursor. Nascent fiber’s structure and performance will largely determine the operability and continuity of the subsequent spinning process, and it has a very big impact on the quality of PAN precursor and carbon fiber. So it is necessary to undertake research on the structure of dry-jet wet spinning PAN nascent fiber.PAN spinning fibers are obtained by dry jet wet spinning process, different drying methods are used to obtain PAN nascent fibers dried samples. Then studied the effect on physical characteristics, surface morphology and internal structure of three methods by contrasting natural drying, air forced drying and freeze-drying. Three methods all caused shrinkage on the nascent fiber samples, cross-sectional area and length of samples were reduced, but with different degree of change. And three drying methods have different effects on the morphology of the surface of the nascent fiber PAN, crystallization characteristics, the amount of residual dimethylsulfoxide (DMSO), and pore structure. The results show that the impact of freeze drying on PAN nascent fibers are minimum, and it can effectively preserve the original structure of PAN nascent fibers spun fibers, so it can be used for sample preparation for testing.The article also studied the influence of solidification conditions on the nascent fiber structure and properties, separately discussed the impact of the coagulation concentration and drawing ratio. As the coagulation bath concentration is gradually increased, the grain size and crystallinity of the spun fiber becomes larger. Sectional shape of spun fibers become round from irregular shape, and the strength and density of the fibers is gradually increased. When concentrations of the coagulation is higher, the nascent fiber has better effect sub-fiber, and the porosity is small. As the drawing ratio of coagulation bath becomes large, the crystallinity and boiling water shrinkage of nascent fiber increase. Meanwhile, the cross-section of nascent fiber tended circular, the holes and other defects inside the fiber become smooth and dense under drawing, the surface trench of fiber is gradually reduced too.Coagulation bath temperature for drawing, drawing influence coagulation bath ratio and concentration on the nascent fiber paper design drawing test machine, get a comprehensive system of data through experiments provide data support for multi-stage coagulation bath drawing. The experiments showed that the best solution was that, the concentration of the first coagulation bath solvent was 70% and the temperature of the coagulation bath was 60℃, with drawing ratio controlled between 5-7 times; the concentration of the second coagulation bath solvent was 75% and the temperature of the coagulation bath was 60℃, with drawing ratio reaching 1.1～1.7 times; the concentration of the third coagulation bath solvent was 80% and the temperature of the coagulation bath was 30℃, with drawing ratio reaching 1.2～1.4 times; the concentration of the fourth coagulation bath solvent was 30% and the temperature of the coagulation bath was 70℃, with drawing ratio reaching 1.1～1.3 times.The most of PAN precursor fibers’ flaws are produced and inherited during the process of nascent fiber. Therefore, it is necessary to undertake an in-depth study for the pore structure of nascent fibers, which is of some significance for producing high-quality nascent fibers and carbon fibers. The experiments study the pore structure of dry jet wet spinning PAN nascent fibers by using hot hole measurement, and compare/contrast with the data of the pore structure of PAN nascent fibers measured by nitrogen adsorption method and drying method. It can be found that as the spinning process, some of the holes in nascent fibers are closed under the action of the draft, the pore size and porosity decreases with the increase of drawing ratio, higher temperature can accelerate this process.