Polyacrylonitrile-based pre-oxidized fibers with improved thermal stability, flame retardant, and mechanical properties were made from the pristine polyacrylonitrile fibers through chemical pretreatment followed by pre-oxidation in air. The morphological structure of the polyacrylonitrile-based pre-oxidized fibers was investigated by Fourier transfer infrared spectra, X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectrometer. The changes of characteristic functional groups and chemical compositions confirmed the successful modification of the polyacrylonitrile fibers during pre-treatment. The grooves and cracks on the surface of polyacrylonitrile-based pre-oxidized fibers were remarkably decreased in comparison with that of pristine polyacrylonitrile fibers. The evolution of crystalline structure of the polyacrylonitrile fibers proved the occurrence of cyclization reactions during pre-oxidation. Meanwhile, thermal stability, flame retardant, and mechanical properties of polyacrylonitrile-based pre-oxidized fibers were also investigated by thermogravimetric analyzer, oxygen index meter, micro combustion calorimeter, and single fiber tensile tester, respectively. The results demonstrated that the polyacrylonitrile-based pre-oxidized fibers initially pre-treated by hydroxylamine hydrochloride, followed by monoethanolamine, had a high limiting oxygen index of 40.1 and breaking strength of 2.03 cN/dtex. The peak of heat release rate and total heat release of polyacrylonitrile-based pre-oxidized fibers decreased significantly while its charred residues increased, contributing to the improved flame retardant property.

中文翻译：

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化学预处理对聚丙烯腈基预氧化纤维结构和性能的影响

聚丙烯腈基预氧化纤维由原始聚丙烯腈纤维通过化学预处理和空气预氧化制成，具有改进的热稳定性、阻燃性和机械性能。通过傅里叶转移红外光谱、X射线衍射、扫描电子显微镜和X射线能谱仪研究了聚丙烯腈基预氧化纤维的形态结构。特征官能团和化学成分的变化证实了聚丙烯腈纤维在预处理过程中的成功改性。聚丙烯腈基预氧化纤维表面的凹槽和裂纹与原始聚丙烯腈纤维相比显着减少。聚丙烯腈纤维晶体结构的演变证明在预氧化过程中发生了环化反应。同时，还分别采用热重分析仪、氧指数仪、微量燃烧量热仪和单纤维拉伸试验仪对聚丙烯腈基预氧化纤维的热稳定性、阻燃性和力学性能进行了研究。结果表明，聚丙烯腈基预氧化纤维最初用盐酸羟胺预处理，然后用单乙醇胺预处理，具有 40.1 的高极限氧指数和 2.03 cN/dtex 的断裂强度。聚丙烯腈基预氧化纤维的放热率和总放热峰值显着降低，而其炭化残留物增加，