1. Introduction to PI Fiber

●Definition: PI fiber, colloquially known as "gold thread," is a crucial high-performance fiber characterized by the presence of imide ring groups in its molecular backbone.

●Composition: Common polyimide molecules contain numerous imide rings, aromatic or heterocyclic rings, which impart high aromaticity and rigidity.

●Strength: Reports indicate that Russian scientists have produced PI fiber second only to PBO fiber with a strength of up to 5.0GPa.

2. Development History of PI Fiber

●1960s: DuPont in the USA began research on PI fiber, but it remained at the laboratory stage due to technological limitations.

●1970s: The former Soviet Union reported military applications of PI fiber, with small-scale production for military use.

●1980s: Austria industrialized PI fiber production using dry spinning technology, launching the product P84 primarily for high-temperature filter materials. France later introduced Kermel fiber with excellent flame-resistant properties.

●1990s: Russian scientists developed PI fiber with a breaking strength of 5.0GPa, significantly advancing the aerospace industry.

●Early 21st Century: Chinese universities and research institutions have conducted systematic and comprehensive studies on PI fiber, achieving certain experimental results.

3. Performance Characteristics of PI Fiber

●Mechanical Properties: PI fiber has a density of about 1.41g/cm³. Heat-resistant PI fibers have a mechanical strength between 0.5—1.0GPa and a modulus of 10—40GPa; high-strength, high-modulus PI fibers have a tensile strength of about 2.5GPa and a modulus exceeding 90GPa.

●Thermal and Flame Resistance: Fully aromatic polyimide fibers typically decompose above 500℃, with a limiting oxygen index of up to 66%. However, the decomposition process may produce harmful substances such as hydrogen cyanide.

●Acid and Alkali Stability: PI fibers are stable in acidic environments, retaining 30%-40% strength after 48 hours in 10% dilute hydrochloric acid; however, they degrade significantly in alkaline conditions.

●Other Properties: PI fibers exhibit good UV radiation resistance and dielectric properties, with a typical dielectric constant around 3.4 and a loss of approximately 10^(-3).

4. Applications of PI Fiber

●Application Areas: Due to their excellent performance, PI fibers are widely used in aerospace, high-temperature protection, electronics, and other fields, especially in high-temperature applications like manufacturing heat-resistant gloves, felts, drums, yarns, filter bags, and ablative materials. Additionally, PI fibers can be woven into fabrics for use in skin materials, pipeline repairs, composite reinforcement, bulletproof materials, and more.