Study on Dyeing Property of Polyimide Fiber by Ammonia Pretreatment

Polyimide (PI) fiber, as a high-performance fiber, possesses advantageous properties, such as outstanding thermal stability, fire resistance, and chemical resistance. It has great potential for use in warm clothing in extremely cold environments and fire-protective textiles, but has poor dyeability. In the present work, PI fiber was pretreated by ammonia and then dyed. The result shows PI fiber could be dyed with basic dyes after the assistance of ammonia. The X-ray diffraction analysis displayed an apparent change in the crystallinity of polyimide fibers. The thermogravimetry analysis illustrated that ammonia penetrated into polyimide fibers, but ammonia pretreatment had an insignificant effect on thermal stability. These changes in polyimide fibers indicated that ammonia could combine with the fiber macromolecules, penetrate inside fibers, and swell the fibers, resulting in elongation of polyimide fiber and decrease in the breaking force. The treated sample had higher color strength than the untreated sample did. The study of dyeing mechanism of PI fibers demonstrates that the Nernst adsorption isotherm is a favorable model for polyimide fiber dyeing with basic dyes.