Polyimide fibers (PI) are a class of heat-resistant and fairly strong synthetic fibers of orange to yellow color. They are prepared by a two-step process from aromatic diamines and aromatic tetracarboxylic dianhydrides. They are often the best choice for very demanding applications where very high temperature, corrosion, wear, and creep resistance is required. The high performance properties are maintained during continuous use to very high temperatures up to 500°F (260°C) and to short-term exposure of 1000°F (550°C).
Polyimides fibers can be produced by a dry-spinning process from a polyamic acid solution. The precursor fibers are then transferred into polyimide fibers by a subsequent heat treatment process.1
PI fibers are rather expensive and difficult to manufacture. But unlike most ordinary fibers like polyester and acrylic, they have a much higher glass transition temperature (about 400°C) and a much higher melting point.
Due to the aromatic structure, PI fibers have very low flammability and excellent chemical resistance to most chemicals. They are also of light weight.
COMMERCIAL Aramid Fibers
A major manufacturer of polyimide fibers is Swicol.
Polyimide fibers are used for very demanding applications. They are used in the elctronic industry for high-performance flexible cables, in the chemical industry as a filter material for hot gases, and in the garment industry as a fiber for heat protective clothing. PI fibers are also used in multi-layer insulation of spacecrafts and atronauts space suits. The gold-like material seen on the outside of some spacecrafts is PI coated with a thin layer of aluminum.
Because of its high price, polyimide fibers are only used when outstanding properties are required.
1Y. Xu, Z. Li et al., J. Mat. Sci., Vol. 48, 22, pp 7863-7868 (2013)