Study On The Degradation And Copolymerization Modification Of Poly(P-Phenylene Terephthalamide)

Poly-p-phenylene terephthalamide(PPTA) fibers have excellent properties and have been widely used in industry and other special areas. The solution polymerization to produce PPTA polymer at low temperature is a mature industrialized method with a long history,while PPTA fiber was prepared by dry-wet spinning from concentrated sulfuric acid solution in the nematic liquid crystal state.Due to the poor solubility of PPTA,it has to be dissolved in concentrated sulfonic acid,and this requires high quality of the equipment during the production process.One fabulous method to improve the solubility of the polymer is to add the third or the forth monomer in the main chain.After the modification,the polymer can be dissolved in polar organic solution and can be spinned directly.This greatly improved the productivity of PPTA fiber.In this paper,the PPTA was synthesized in our lab and its degradation during the dissolution and defoamer process was studied by using simulative spinning model.After the third monomer was added during the polymerization,the structure and thermal properties of the polymer and the rheological behavior of spinning solution were studied. Here,the impact of the particle size distribution,solution temperature, dissolving time,solution concentration and the concentration of H₂SO₄to the inherent viscosity of PPTA and degradation rate have also been systematically studied.The results showed that the preferred condition of dissolving process were particle size 100μm,solution temperature 83℃, solution concentration 18.5wt%,H₂SO₄ concentration 100wt%and dissolving time 1 hour.Besides,the factors that may cause degradation of Poly(p-phenylene terephthalamide)(PPTA ),such as CaCl₂, N-Methyl-2-pyrrolidinone(NMP),H₂O and Ca(OH)₂ content in the spinning solution were studied.Furthermore,influence caused by the degradation of PPTA to the structure and thermal properties has also been discussed.In this paper,copolymer which has been added 3,4'-diaminodiphenyl ether(3,4'-ODA) as the third monomer during the copolymerization process was specially discussed,as it has a great influence to the heat resistance of PPTA..Moreover,the thermal decomposition kinetics of this polymer and the rheology property of the polymer solution were systematically studied.The result showed that the polymer solution was a typical shear thinning fluid.The viscosity of copolymer dope decreased when the shear rate was increased.The apparent viscosity of copolymer dope decreased with the increase of temperature while increaseed with the decrease of concentration.The non-Newton Index,which shows the non-Newton property,decreased with the increase of tempreture,and increased with the increase of polymer concentration.