Study On Structure And Properties Of Heterocyclic Aramid Fiber With Heat Treatment

Heterocyclic aromatic polyamide fiber (heterocyclic aramid fiber) is a kind of high performance fiber with high strength, high modulus, high temperature resistant and excellent dimensional stability. With its excellent mechanical and thermal properties, heterocyclic aramid fibers are widely used in military, aviation, high-performance composite materials fields. In this paper, its structure and performance would be studied in three parts.Heat treatment process is the key to prepare heterocyclic aromatic polyamide fiber.The effect of the heat treatment temperature and heat treatment time on the mechanical properties of the fiber was discussed in this paper. First of all, the heat treatment temperature range was determined through the dynamic thermal mechanical analysis (DMA) and thermo-gravimetric analysis (TGA). The influence of the heat treatment temperature and heat treatment time on the mechanical properties of the as-spun fiber was discussed. The structure of fibers before and after heat treatment were compared through the scanning electron microscope (SEM), X-ray diffraction (XRD), degree of orientation analysis and Fourier transform infrared spectroscopy (FTIR). Finally, the optimum heat treatment process conditions were as follow:dynamic heat treatment, nitrogen atmosphere, heat treatment temperature was420℃, the heat treatment time was3.7min. Under the optimum conditions, strength and modulus of resulted heterocyclic aromatic polyamide fiber was23.86cN/dtex and1041.43cN/dtex.In this paper, thermal properties of heterocyclic aromatic polyamide fiber were studied through TGA/DTA-FTIR, Fourier transform infrared spectroscopy (FTIR),TGA-DTA/MS and thermo-gravimetric analysis(TGA). It could be seen from TGA curve that the decomposition occurred after the temperature arrived at520℃.There is little difference between the thermal stability of the fibers before and after heat treatment. In nitrogen atmosphere, the residue of the fiber was59%at900℃. The structure of volatile and residue of the fiber in thermal decomposition were analyzed through TGA/DTA-FTIR,Fourier transform infrared spectroscopy (FTIR).The supramolecular structure of heterocyclic aromatic polyamide fiber began to fracture from550℃. Benzene ring and imidazole ring began to crack at700℃. H2O, aromatic ring structure compounds, CO2, CO, nitrogen oxides, NH3, HCN and other small molecular product were released in the thermal decomposition process. Combining TGA-DTA/MS results, It showed that heterocyclic aromatic polyamide fiber yielded the most types-pyrolysis products between500℃to650℃.Fiber decomposition degree was the largest between500℃to650℃.The thermal decomposition rate of fiber was maximum at550℃.Dynamic mechanical properties of the heterocyclic aromatic polyamide fiber were discussed through the dynamic thermal mechanical analysis (DMA) in this paper. Its storage modulus greatly reduce at200℃.The peak of its loss modulus appeared at260-290℃. Glass transition temperature of heterocyclic aramid fiber increased with the frequency increased. The apparent activation energy of the glass transition was275.2kJ/mol.