Structural Evolution and Mechinical Properties of Copolyamide Fibers during Thermal Annealing

Abstract

Modified aramid (PBIA) containing benzimidazole units in the main chain were synthesized and the corresponding PBIA fibers were prepared by wet spinning and then annealed at different temperatures. The mechanical properties and the structure of copolyamide PBIA fibers were investigated for different annealing temperatures. The results of thermogravimetric analysis showed that the decomplexation reaction between HCl and benzimidazole occurred during the annealing process and HCl was completely removed at 320°C. The decomplexation of HCl also leads to the formation of hydrogen bonds between benzimidazole fragments, resulting in the rearrangement of the molecular chain and a more ordered macromolecular structure. The mechanical properties, chain orientation could be significantly improved when the samples were annealed in the temperature range from 280 to 320 °C. In addition, the analysis of self-elongation during the annealing process further indicates that the macromolecular chains were more ordered after the decomplexation of HCl. In addition, the PBIA fibers firstly annealed at 300°C which the decomplexation reaction between HCl and benzimidazole occurred, and then annealed at 400°C, resulting the higher PBIA fibers are obtained.