Study On The Polymerization Technique Of Poly (P-phenylene Terephthalamide) (Aramid Fiber 1414)

Aramid fiber, especially the para-aromatic fiber(hereinafter PPTA) depending on the largest consumption and wide application rang has occupy a dominant position in the three kinds of high performance fibers due to the excellent mechanical property and thermal properties.Until now, the few capitalist countries grasp more than 90% of the world market because of the complex production process, furthermore, to obtain the PPTA fiber, the polymer must be dissolved in the concentrated sulfuric acid.With the development of the high-tech industry and the national defense demand, the requirement of PPTA is more and more significant. The polymer of the PPTA is prepared from the solvent system of NMP-CaCl2 in the domestic and overseas. However, the moisture content of the domestic NMP is too high to be used in the polymerization of PPTA, because that the TPC is liable to be hydrolyzed. Though the high quality NMP can be import from the Japan, the problem of solvent recovery is not yet solved. All the matters caused the cost problem restrict the industrialization process of PPTA.In this paper, we used the low toxicity and low salinity DMAC-LiCl solvent system as the reaction zones. The polymerization process of general PPTA was researched in the DMAC-LiCl solvent system, and theηinh of the polymer was≥3.88. The FT-IR was used to characterize the structure, and the TGA was used to detect the thermal stability of the polymer, the result showd that the decomposition temperature of the polymer was 550℃, and the liquid crystalline properties of polymer was also analyzed by means of polarizing microscope. The result showed that all the property of the polymer was consistent with that of Kevlar29.Aiming at the problem that the polymer only can be dissolved in the concentrated sulfuric acid, the 4,4'-diaminodiphenyl is added to change the structure of PPTA. When the 4,4'-diaminodiphenyl content was more than 40mol% of the diamine, the copolymer solution were changed from gel system to well distributed heavy-bodied state, and the solubility behavior is consisted with the result of XRD studies. We also chose some typical organic solvent to examine the dissolving ability of the copolymer, the solubity of the copolymer is obvious improvement. The structure of the copolymer was characterized by FT-IR. The thermal stability was studied by means of TGA. Method of coagulation bath precipitation combined with SEM are used to observe the morphology of copolymer, the result showed that the copolymer performs good fiber-forming property.The poor dissolving capacity also limited the characterization methods to analyze the performance of PPTA and modified PPTA, and the alkylation method was introduced to break the hydrogen bonding structure of the polymer in order to use the GPC to test the molecular weight distribution. The consequence further suggested that the PPTA polymer and copolymer which were synthesized in the DMAC-LiCl solvent system had the advantage of narrow molecular weight distribution.