Study On Preparation, Structure And Properties Of Para-Aramid Copolymer Fibers

Poly（P-phenyleneterephthalamide） （PPTA） fiber is a kind of high performance fiber with high modulus and high strength, and can be used in many high technology fields, such as aviation, cable, and composites. The high molecular weight PPTA is polymerized by 1,4-phenylenediamine hydrochloride and terephthaloyl chloride in polar organic solvents such as N-Methyl-Pyrrolidone at low temperature. PPTA can only be dissolved in concentrated sulfuric acid and the dope is lyotropic liquid crystal, PPTA fiber were prepared by dry-wet spinning. For use the concentrated sulfuric acid as solvent, it meets a lot of difficult, such as the corrosion of equipment and equipment protect. In order to improve the solubility of PPTA, introducing a third monomer into the macromolecular chain is a efficient method. Then the copolymer solution can be spun directly into filaments. With this method , the process and productivity is improved.In this paper, high molecular weight (η_inh>2 dl/g) para-aramid copolymer were synthesized. The effect of the reaction time, reaction temperatures, monomer concentration, concentration of pyridine, the molar ratio of 3,4’-ODA in the polymerization was discussed. The result shows that, the optimal process is as follows: the reaction time is between 20-30min, and the later reaction temperature is 80℃, the best molar ratio of 3,4’-ODA is 25%, and the best concentration of CaCl₂ is 0.8%wt. the resultant polymer has the highest molecular weight.The rheological behavior of para-aramid copolymer solution was studied. The rheological parameters of copolymer solution, such as Non-Newton exponent, viscous flow activation energy and structural viscosity index were discussed, which could provide an important basis to determine the spinning process. The results of the study on the rheology indicated that the copolymer solution was shear thinning fluid. The apparent viscosity of copolymer solution decreased with the increase of temperature. The non-Newton Index increased from 0.6 to 0.8. And the viscous flow activation energy decreased from 15 to 20 with the increase of shear rate. Dynamic rheological experiments shows that the loss modulus and storage modulus of the polymer solution closely linked with molecular weight and temperature. With the increase of molecular weight, the loss modulus and shear modulus increased. We also found that the Cox-Merz rule not suitable for the para-aramid copolymer solution.Using NMP/H₂O system as coagulation bath, the dope of para-aramid copolymer in NMP was spun from the spinneret by wet-spinning method and the corresponding fibers were prepared. The tensile strength of initial fiber increases with the increase of spinneret draw ratio. We can got as-spun fiber with good properties by using 15%wt NMP solution as coagulation bath. Experiments results show that the fiber strength increased with the draw ratio increase. The most appropriate heat drawing ratio is 2.2,and 420℃is the best drawing temperature. The protection of nitrogen atmosphere is helpful. Under above conditions, para-aramid copolymer fibers with good properties were obtained: the strength is 649.4MPa、breaking elongation is 2.38%、crystallinity is 39.18%, and the orientation is 83.5%.The new ideas mainly brought forward in this paper are as follows: 1. rheology behavior of para-aramid copolymer solutions were discussed. 2. The wet-spinning of para-aramid copolymer fibers were studied systematically,...