Study On The Wet-Spinning Coagulation Mechanism Of Meta-Aramid Fiber

Meta-aromatic polyamide （PMIA） was first synthesized in 1962 by DuPont. Because of its excellent high temperature resistance, flame resistance and textile processing performance, its fiber and paper products are widely used in industry and dress fabric, but also play an irreplaceable role in the occasion of high temperature. With the increasing demand for high-performance fibers, meta-aromatic polyamide products have been developed rapidly.At present, the meta-aramid is polymerized mainly by solution polymerization, interfacial polymerization. Spinning methods of PMIA fibers are mainly wet spinning and dry spinning. Researchers all of the world have studied a lot on wet spinning coagulation mechanism of PAN fibers and coagulation theory of it has been established. However, the wet spinning coagulation mechanism of PMIA has not been studied. Meta-aramid fibers were commercialized not too long ago in our country. In order to get high-performance meta-aramid fibers, it’s very important to study the coagulation mechanism of wet spinning process.First of all, the Photographic method and Gravimetric method were used to study the extrusion die-swell and the extrusion activation energy of meta-aramid spinning solution. The study found: extrusion die-swell phenomenon existed in the extrusion process of meta-aramid spinning solution, and the extrusion die-swell of the spinning solution increased with the increase of spinning pressure; decreased with the increase of spinning nozzle’s L/D, filter cloth layers and the temperature; the extrusion die-swell of the wet spinning was more than that of the dry-jet wet spinning. With the shear rate increasing, the extrusion activation energy would decrease. This was good for the stability of spinning process.Secondly, component analysis was used to study the wet-spinning coagulation mechanism of PMIA. UV spectrophotometer and complexometric titration were chosen to measure the content of DMAc and CaCl₂ in the fiber’s extract liquid respectively. The accuracy and reliability of the two methods were also discussed in this paper. In addition, the method of collecting sample was also discussed preliminarily in this study, and finally the appropriate sample collecting method and the number of spinning nozzle hole were selected. Finally, the effect of spinning process was studied in this paper （such as: jet stretch, coagulation bath temperature, and coagulation bath concentration） by determinate the diffusion coefficient of the meta-aramid wet spinning. This could help us to obtain the optimal spinning process parameters.The study found: In the measurements of the diffusion coefficients, the values of solvent coefficients were larger than those of nonsolvent coefficients. As the increase of jet stretch, coagulation bath temperature and the concentration of DMAc in coagulation bath, both the solvent and nonsolvent diffusion coefficient increased. Through analysis we can see, while at smaller jet stretch and lower coagulation bath temperature the D_s/D_n decreased. Coagulation process is essentially a deposition process that the polymer separated from the original solution, and this process directly determined the fiber structure. The SEM analysis shows: as the coagulation bath temperature increased, the internal cavity defects in the fiber increased. Therefore coagulation bath temperature should be controlled in an appropriate scope as far as possible in the spinning process. With the concentration of coagulation bath increasing, the internal structure of fibers could be better.The new ideas of this paper are:1: The extrusion die-swell of the meta-aramid solution was studied in this paper systematic, and the effects of process conditions on the extrusion die-swell were discussed. The results would favorite the production of the meta-aramid fibers.2: The wet spinning coagulation mechanism of meta-aramid fibers have not been reported yet. In this article, an innovative inter-component analysis was used to study the wet spinning coagulation mechanism of meta-aramid dope and the diffusion coefficient was measured, and the impact of conditions on the diffusion coefficient was also discussed in spinning process.