M5 fiber (polyhydroquinone-diimidazopyridine) is a high-strength synthetic fiber first developed by Doetze Sikkema and his team at the Dutch chemical firm Akzo Nobel. It is produced in the United States by Magellan Systems International LLC.
M5 fiber is prepared by a condensation polymerization between tetraaminopyridine and dihydroxyterephthalic acid using diphosphorus pentoxide as a dehydrating agent. The polymer mixture is then heated and extruded to form brightly blue polymer fibers. The fibers are then washed extensively with water and base in order to remove the phosphoric acid generated by the hydration of diphosphorus pentoxide from the polymer.
To remove water from the fiber structure and enable the intermolecular hydrogen bonds to be created, thus increasing the strength of the polymer, the fiber is heated and exposed to controlled stress. This aligns the molecular structure of the fiber in a better configuration for tensile and compressive strength.
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M5 is more fire resistant than meta-Aramid. It is the most fire resistant organic fiber yet developed. It is less brittle than carbon fiber and will yield when stretched.