Preparation of High Performance Copolyimide Fibers via Increasing Draw Ratios

High performance fibers based on copolyimide (co-PI) containing benzimidazole and ether moieties were prepared via a two-step wet spinning method. The effects of draw ratio on the structures and properties of the fibers are investigated. The mechanical properties of the co-PI fibers are improved greatly by increasing draw ratio at temperatures above 400 degrees C, reaching the optimum tensile strength of 2.8GPa and modulus of 136GPa, which is due to the development of the molecular orientation along the fiber direction. The hot drawing process roughens the fiber surface and stretches the molecules in the fibers. Moreover, the fiber structure evolutions during the drawing process were also discussed and a smectic A liquid crystal-like model was proposed.