Research Progress and Application of Polyimide Fiber

Polyimide fiber is a new type of high-performance organic fiber with excellent properties such as high strength, high modulus, low dielectric constant, resistance to high and low temperatures, radiation resistance, and flame retardancy, making it highly promising in the market. This paper reviews the research progress of polyimide, fiber preparation, fiber properties, modification methods, and applications, while also providing insights into its future development trends.

Keywords: Polyimide fiber; Preparation; Modification; Application; Research progress

1. Research Status of Polyimide Fiber

Polyimide is a polymer with a rigid imide ring in its molecular backbone, forming a ladder-like structure with benzene rings and imide groups, resulting in strong intermolecular forces. These structural characteristics endow it with high strength, high modulus, heat resistance, and flame retardancy, leading to extensive applications in environmental protection, reinforcement, protection, textiles, and apparel.

Polyimide fibers were first developed in the 1960s by DuPont in the United States but were not industrialized due to high production costs and immature technology. By the late 20th century, with advancements in synthesis and spinning techniques, along with the growing demand in specialized fields, research into polyimide fibers gained momentum. Various companies in France, Austria, and Russia developed flame-retardant and high-strength polyimide fibers with superior properties.

In China, research on polyimide fiber remained largely at the experimental level for many years. However, since 2010, industrialization efforts have accelerated. For example, Jilin University and Changchun Gaoqi Polyimide Materials Co., Ltd. developed heat-resistant polyimide fibers, while Beijing University of Chemical Technology and Jiangsu Xiannuo New Materials Technology Co., Ltd. established a production line capable of producing 30 tons of high-performance polyimide fiber annually.

2. Polyimide Fiber Preparation

2.1 Synthesis Process

Two main synthesis methods exist:

• Forming the polyimide ring structure during polymerization.
• Using preformed imide-containing monomers for polycondensation.

The first method is more commonly used, with two-step and one-step approaches available. The one-step method directly produces polyimide from diamine and dianhydride monomers in a high-boiling-point phenolic solvent but has environmental drawbacks due to solvent toxicity. The two-step method involves an intermediate polyamic acid stage before final polyimide formation, offering better environmental safety and broader applicability.

2.2 Spinning Processes

2.2.1 Dry Spinning

This method produces precursor fibers from polyamic acid, which are then converted into polyimide fibers via thermal treatment. It avoids coagulation baths and is relatively efficient and environmentally friendly, though fiber quality can be affected by post-processing steps.

2.2.2 Wet Spinning

Here, fibers form through precipitation in a coagulation bath before being stretched and thermally treated. This method requires extensive equipment and higher production costs but enables better fiber structure control.

2.2.3 Dry-Wet Spinning

This hybrid approach combines the advantages of dry and wet spinning, allowing improved fiber formation control. NASA has used this technique to develop high-performance polyimide fibers.

3. Properties of Polyimide Fiber

3.1 Thermal Stability

Polyimide fibers decompose at around 500°C and maintain structural integrity even at 250°C. Some variants exhibit thermal stability up to 600°C, making them among the most heat-resistant polymers.

3.2 Physical and Chemical Properties

Polyimide fibers feature high strength and modulus, superior to many high-performance fibers like aramid and PBO. However, their rigid structure results in poor dyeability and alkali resistance. They also exhibit excellent radiation resistance, retaining 90% of their strength even after exposure to high radiation doses. Their dielectric properties and resistance to extreme cold further enhance their industrial value.

4. Polyimide Fiber Modification

4.1 Flexibility Improvement

Due to the high density of benzene rings in their backbone, polyimide fibers have high stiffness, leading to brittleness and poor textile performance. Researchers have introduced flexible groups into the polymer chain to enhance fiber flexibility and processability.

4.2 Low-Temperature Plasma Treatment

Surface modification using low-temperature plasma can improve polyimide fiber hydrophilicity without compromising mechanical properties. Experiments have shown that treating polyimide fibers at 25 Pa pressure and 130 W power for 240 seconds significantly enhances hydrophilicity while maintaining strength.

4.3 Composite Modification

Researchers have combined polyimide fibers with carbon nanotubes, copper coatings, and polyaniline to create conductive, lightweight, and mechanically robust composite fibers. These innovations extend their applications in antistatic fabrics, lightweight conductors, and protective materials.

5. Applications and Future Development

5.1 Applications

5.1.1 Environmental Protection

Polyimide fibers are used as high-temperature dust filtration materials, benefiting industries like waste incineration and industrial exhaust purification.

5.1.2 Reinforcement and Protection

Their high strength and resistance to extreme conditions make them ideal for aerospace, nuclear energy, and military applications, including spacecraft cable sheathing and aircraft structural materials.

5.1.3 Textiles and Apparel

Polyimide fibers are increasingly used in civilian textiles due to their insulation and thermal properties. They are blended with other fibers to create winter clothing and incorporated into protective masks as filtering layers.

5.2 Development Recommendations

5.2.1 Industrialization

With growing demand in high-tech sectors, industrial production of polyimide fibers needs to be prioritized. This requires government policy support, technological innovation, and overcoming production barriers.

5.2.2 Process Optimization

Reducing production costs, increasing yield, and refining key processes will enhance polyimide fiber competitiveness and contribute to advanced material development.

5.2.3 Market Expansion

Further applications in aerospace, defense, and high-strength materials should be explored, strengthening China’s position in high-performance fiber markets.

6. Conclusion

Polyimide fibers possess excellent mechanical, thermal, and flame-retardant properties, making them valuable in multiple industries. To fully realize their potential, industrialization, process refinement, and application expansion must be prioritized. Future research should focus on enhancing fiber properties to meet evolving market needs.

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