Polybenzimidazole or PBI fiber (1983) is a synthetic fiber with an extremely high melting point that also does not readily ignite, because of its exceptional thermal and chemical stability. The Federal Trade Commission definition for PBI fiber is "A manufactured fiber in which the fiber-forming substance is a long chain aromatic polymer having recurring imidazole groups as an integral part of the polymer chain". Kermel, a polyamidoimide, is a related "high performance polymer."
PBI is used to fabricate high-performance protective apparel such as firefighter turnout coats and suits, astronaut space suits, high temperature protective gloves, welders' apparel, race driver suits, braided packings, and aircraft wall fabrics.
PBI is prepared by step-growth polymerization from 3,3',4,4'-tetraaminobiphenyl and diphenyl isophthalate (an ester of Isophthalic acid). The resulting polymer is processed as a solution in dimethyl acetamide via a dry spinning process.
The first U.S. commercial PBI fiber was produced by Celanese.
|Acids - concentrated||Poor|
|Acids - dilute||Fair-Poor|
|Greases and Oils||Good|
It is dyeable to dark shades with basic dyes following caustic pretreatment and resistant to most chemicals.
|Dielectric constant @ 1 MHz||3.2|
|Dielectric strength||21 kV·mm-1|
|Volume resistivity||8x1014 Ω·cm|
Features low electrical conductivity and low static electricity buildup.
|Coefficient of friction||0.19-0.27|
|Compressive modulus||6.2 GPa|
|Compressive strength||400 MPa|
|Elongation at break||3%|
|Hardness - Rockwell||K115|
|Izod impact strength||590 J·m-1 unnotched|
|Tensile modulus||5.9 GPa|
|Tensile strength||160 MPa|
Features abrasion resistance.
|Char Yield (under pyrolysis)||High|
|Flammability||Does not burn|
|Limiting oxygen index||58%|
|Water absorption - over 24 hours||0.4%|
Additional features: will not ignite or smolder (burn slowly without flame), mildew- and age-resistant, resistant to sparks and welding spatter.
|Coefficient of thermal expansion||23×10-6·K-1||Low|
|Heat-deflection temperature - 0.45 MPa||435 °C (815 °F)||High|
|Thermal conductivity @ 23 °C (73 °F)||0.41 W·m-1·K-1||Low|
|Upper working temperature||260–400 °C (500–752 °F)||High|
Other features: continuous temperature: 540 °C (1,004 °F), melting temperature: 760 °C (1,400 °F) under pyrolysis, retains fiber integrity and suppleness up to 540 °C (1,004 °F).