Efficient production of copolymerized PA6-based polymer fibers: Oligomer control and direct melt spinning

Synthesis of PA6-based polyester amides (PEAs) is the one of main way to expand the application of PA6. Due to the residual oligomers in the polymer matrix, PEAs are also difficult to achieve directly melt spinning similar to PA6. In this work, the molecular structure designable PEA synthesis method proposed in our previous work was further investigated to control the oligomer content control by end-amino shielding at open-loop stages and efficient de-volatilization at polycondensation stages. The effect of the molecular weight of PA6 segments on oligomer formation was also investigated. The results show that the oligomers, caprolactam, and cyclic dimer contents of PEAs are reduced to 2 wt%, 0.38-0.76 wt%, and 0.2-0.3 wt%, which is lower 75%, 85%, and 50% compared to industrially produced PA6, respectively. It indicates that the molecular weight of PA6 segments, in addition to affecting the physicochemical properties, can also thermodynamically enable regulation of the type of oligomer generated. By adjusting the chain segment structure and controlling the reaction conditions, all PEAs can be directly melting spinning (1200 m/min) and maintains good physical and chemical properties. At the same time, the substantial reduction in oligomers means that PEAs can completely eliminate post-processing such as hydrothermal extraction, fiber production time is shortened from more than 40 h (PA6) to less than 15 h and resource consumption is reduced by more than 30%. This oligomer control method is also applicable to functional PA6, which lays the foundation for efficient and sustainable industrial production of copolymerized PA6 functional fibers on a large scale.