| Aromatic polyamide fiber is a kind of important organic synthetic fibers.Nitrogen-containing heterocyclic aramid fibers,which contain benzene-cyclic and heterocyclic in their molecular backbone,have excellent physical mechanical properties,thermal oxidation stability,flammability and electrically insulating,especially high-temperature resistance.They are widely used as preference structural materials in aerospace and military industry,particularly in making high-performance military products.The study of thermal resistance can provide valuable information to understand the mechanism of chemical change during the thermal suffering,which is significant to the preparation,modification and application of these polymer and fibers.In this paper,the status of research and development about domestic and foreign heterocyclic aramid were summarized,and the application of thermo-analysis combination techniques in the thermal analysis of polymer was discussed systemically.The thermal resistance and structures of domestic and heterocyclic aramid fibers,as well as the homemade whole heterocyclic aramid polymer and fibers were prepared,and on this base,the behaviors of thermal degradation of PPTA fiber,F-12 fiber,aramid ?,and SVM-based polymer and fibers were investigated in inert gas and air by the means of thermo-gravimetric coupled with Fourier transform infrared spectroscopy(TG-FTIR),pyrolysis-gas chromatography/mass spectrometry(Py-GC/MS)and thermo-gravimetric coupled with mass spectrometry(TG-MS).Their mass loss,volatile fragments,residue and kinetics were analyzed in detail by above methods.As different proportions heterocyclic linkages being introduced into F-12 fiber and aramid III on the base of PPTA fiber,these fibers differ in thermal stability and the process of pyrolysis,and the overall performance of thermal resistance was F-12 fiber>aramid III>PPTA fiber.Combined the FTIR spectrum of volatile fragments and residue,in the low temperature,amide bonds began to break and as the temperature increased,the thermal degradation strengthened and the fiber carbonized.Pyrolysis products of fibers at different temperatures were obtained by Py-GC/MS,which also offered foundation for the analysis of TG-MS.During the process of pyrolysis,benzene ring compounds formed would further decompose and recombine to form relative stable compounds.In the mass spectrum,due to the heterocyclic linkages,F-12 fiber and aramid III showed more extensive range of ion current peaks than that of PPTA fiber,and hydrolysis,hemolysis,oxidation emphasized differently at different temperature range.SVM-based polymer,as-spun fiber and drawn fiber were all one-step degradation in both inert and air atmosphere.In the inert atmosphere,during the thermal degradation of Py-GC/MS,the break of molecular chain was mainly de-polymerization reaction.And then these kinds of benzene ring compounds happened to the second pyrolysis or recombine to form stable benzene ring compounds.Besides,much more stable small molecular species would be generated with the temperature increasing.And as different thermal stability,the three kinds of SVM-based polymer and fibers showed about 10?20? diversity in degradation temperature.The analysis for TG-MS in helium further verified the results of Py-GC/MS.In the air atmosphere,the ion current peaks became wider,showing that some unstable benzene ring compounds underwent complex structure change and recompose;meanwhile stable benzene ring compounds would be formed or then oxidized to oxy-carbide and oxy-nitride compounds.Besides,TG-DTG curves of six kinds of materials were obtained at different heating rates(5,10,15,20?/min).And their kinetic parameters and equations were investigated based on Kissinger,Friedman and Flynn-Wall-Ozawa methods.The research results showed that F-12 fiber,aramid-?,and SVM-based aramid all behaved more excellent thermal stability than that of PPTA fiber,and the thermal stability SVM-based drawn fiber>SVM-based as-spun fiber>SVM-based polymer. |
PDF Full Text Request