Color construction of polyimide fibers based on charge transfer complex regulation and swelling effect

[Display omitted] •Modify the surface structure of PI fibers with three organic carriers.•Mechanism based on charge transfer complex regulation and swelling effect.•The biggest surface layer modified depth of the fiber is 10.0% of the fiber radius.•The dyeing properties of the fibers changed obviously. High glass transition temperature and charge transfer complex (CTC) of polymeric chains in polyimide (PI) fibers are known as big obstacles for good dyeing properties. To address this issue, a novel dyeing mechanism involving CTC regulation and swelling effect was proposed to explain the dyeing improvement of polyimide fibers with suitable carriers. It is believed that the carrier with certain structures can adjust the CTC effect of the polyimide fibers, so that the original color of polyimide can be changed, and more dyes can be adsorbed. Based on this mechanism, three organic carriers, including N-methylformanilide (MFA), phenoxyethanol (PPA) and dimethylacetamide (DMAc) were utilized for the treatment and dyeing of polyimide fibers. Notably, much deeper dyeing color was obtained for the fibers dyed with MFA than the other two carriers, which can be ascribed to the capability of MFA for the CTC transformation in the PI fibers. Moreover, the fibers dyed by MFA and PPA have good color fastness, while the fibers dyed by DMAc have obvious ring dyeing phenomenon and poor color fastness, which corresponds to the swelling depth of the fibers. These results will provide a basis for the selection of carrier for efficient color construction of polyimide fibers.