PA6T is one of the most typical high-temperature resistant polyamides, which is widely used in military, transportation and communication fields. As an engineering plastic, thermal stability is a very important point, although there are many studies on copolyamide PA6T, but the in-depth analysis of its heat resistance and thermal degradation process is rarely studied. Therefore, two copolyamides, PA6T/66 and PA6T/610, were synthesized by high temperature and high pressure solution polycondensation method, and their thermal degradation processes and kinetic mechanisms were analyzed in depth. Firstly, the structure and composition of both were characterized by Fourier transform infrared spectroscopy (FTIR) and hydrogen nuclear magnetic resonance spectroscopy ( 1 H NMR). The results showed that copolyamide was synthesized successfully. Thermogravimetric analysis (TGA) and thermogravimetric infrared comprehensive analysis (TG-IR) were used to analyze the heat resistance and degradation products of the two copolyamides PA6T. The results of TGA showed that the initial decomposition temperature of the two copolyamides was about 400°C, and the temperature of PA6T/610 was slightly higher. TG-IR results showed that both copolyamides maintained good thermal stability before 350°C, without the generation of degradation products and their corresponding obvious characteristic absorption peaks. Thermal decomposition products increased significantly at about 400°C, and gradually became complete after 450°C. By comparing the Kissinger method, Flynn-Wall-Ozawa method (FWO), and Coats-Redfern method (CR), the thermal degradation activation energy and kinetic reaction mechanism of the two copolyamides were obtained.
PA6T/66 and PA5T/56 with stable molecular weight and molecular weight distribution were prepared by one-step polymerization. The relationship between the structure and physicochemical properties of two kinds of polyamide samples was analyzed by software analysis and instrument test. The results show that the hydrogen bond between molecular chains has a significant effect on the properties of the materials. From the microscopic point of view, the mechanical properties of PA5T/56 molecular model were generally better than those of PA6T/66 molecular model because the hydrogen bond was not considered. At the macro level, the result was just the opposite because of the hydrogen bonds between the molecular chains. The Gibbs free energy of PA5T/56 dehydration condensation reaction was larger, indicating that the polymerization rate was faster, which was consistent with the actual situation. PA6T/66 belongs to the triclinic α crystal system, PA5T/56 belongs to the hexagonal γ crystal system, PA6T/66 T g = 105.50℃, T c = 257.34℃, T m = 295.74℃, the ΔG PA6T/66 and ΔG PA5T/56 = 36.84 kJ/mol and 34.27 kJ/mol respectively indicate that the heat resistance and thermal properties of PA6T/66 were better than those of PA5T/56.
Yang Yuhao,Pu Zejun,Meng Chihan,Zhong Jiachun,Pang Jiahong,Yang Kaijie,Yue Mengjie,Wu Fang
Semi-aromatic polyamides have excellent comprehensive properties and can effectively adjust thermodynamic properties through monomer composition and ratio to meet different application requirements. Therefore, in this study, two copolyamides (PA6T/66 and PA6T/610) were synthesized by one-pot method and their thermal and mechanical properties were subsequently analyzed and compared. Firstly, the chemical compositions and microstructures of the two copolyamides were characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance hydrogen spectroscopy ( 1 H NMR), wide-field X-ray diffraction (XRD) and polarized ophthalmic microscopy (POM), and the viscosities [η] of the specimens were tested. Secondly, the heat resistance of the two copolyamides was analyzed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Subsequently, the mechanical strength of the two copolyamides was evaluated. The FTIR, NMR and XRD results show that the molecular structure and crystal morphology of the two copolyamides are highly similar, which may prove the success of the target products. The TG results show that the heat resistance of the two copolyamides is very good, with the extrapolated initial decomposition temperature above 430 °C, and PA6T/66 has better heat resistance. The DSC results show that PA6T/66 has a higher melting and glass transition temperature. The mechanical test results show that PA6T/66 has greater tensile and flexural strengths of 70 MPa and 110 MPa, respectively, while PA6T/610 has better impact toughness. The above comparative results can be extended to determine the differences in performance between long-chain and short-chain polyamides, which can provide a reference for future related research. Graphical abstract
危险品化学品经营许可证（带存储）