*Article* **Enhancing the Dyeability of Polyimide Fibers with the Assistance of Swelling Agents**

### **Dongyan Shao, Changhai Xu, Hongbo Wang \* and Jinmei Du \***

Key Laboratory of Eco-textiles, Ministry of Education, College of Textiles and Clothing, Jiangnan University, Jiangsu 214122, China; dongyan-shao@foxmail.com (D.S.); changhai\_xu@jiangnan.edu.cn (C.X.)

**\*** Correspondence: wxwanghb@163.com (H.W.); jinmei\_du@jiangnan.edu.cn (J.D.)

Tel.: +86-130-5730-7010 (H.W.); +86-138-1205-0292 (J.D.)

Received: 27 December 2018; Accepted: 21 January 2019; Published: 22 January 2019

**Abstract:** Polyimide (PI) fibers have outstanding thermal stability and mechanical properties, but are difficult to dye with disperse and basic dyes. In this work, it was proposed to use N-methylformanilide (MFA), phenoxyisopropanol (PIP), and acetophenone (AP) as swelling agents to enhance the dyeability of PI fibers. The PI fibers treated with swelling agents were characterized by thermal gravimetric analysis, scanning electronic microscopy, tensile testing, and crystalline analysis. It was found that the swelling agents penetrated into the PI fibers in amounts greater than 10% (pertaining to the weight of PI fibers). The swelling agents did not really swell the PI fibers, but broke the interaction forces between the PI macromolecules. With the assistance of swelling agent, the PI fibers could be dyed with disperse and basic dyes in strong color strengths. AP exhibited the best performance for enhancing the dyeability of PI fibers, followed by MFA and PIP. The dyed PI fibers were found to have good colorfastness to washing.

**Keywords:** Polyimide fiber; thermal stability; swelling agent; dyeability
