The U.S. Naval Research Laboratory (NRL) Chemistry Division and Technology Transfer Office has approved the commercial manufacturing of an PEEK-like phthalonitrile (PN) resin composition, developed by the laboratory.

Phthalonitrile-based polymers are high temperature thermosets that remain strong at temperatures up to 500°C and can be processed into shaped fiber reinforced composite components using non-autoclave techniques.

‘The many attractive features of the second-generation polyetheretherketone PEEK-like phthalonitriles make these resins excellent candidates for numerous military and domestic applications,’ said Teddy Keller, head of NRL Advanced Materials Section, who invented the material along with Matthew Laskoski, and Andrew P. Saab. ‘The NRL-developed phthalonitrile-based polymeric composites exhibit superior flame resistant, high temperature, and low water absorption properties that do not exist in the current marketplace.’

The resin can be used to make components using resin transfer molding (RTM), resin infusion molding (RIM), filament winding, prepreg consolidation, and potentially using automated composite manufacturing techniques such as automated tape laying and automated fiber placement.

Military applications

The material is reported to have dielectric permittivity and loss tangent characteristics for potential high temperature radomes and other applications requiring radiofrequency transparency. The viscosity of the curing PN composition can be controlled as a function of the curing additive and temperature and the B-staged prepolymer intermediate can be stored indefinitely under ambient conditions until ready to convert to the thermoset polymer or to use in the fabrication of a composite component.

Due to their low water absorption, processing temperatures comparable to common epoxy resins, and improved thermo-oxidative stability at temperatures in excess of 375°C, the polymers are suitable for applications such as  lightweight automobiles, ships, oil rigs, aircraft, wind blades, high temperature bearings, valves, battery and electronic casings, fire resistant textiles, robotic and autonomous firefighting on ships, ammunition casings and storage containers, and fire-resistant building materials.

Shelf life

It is also possible to melt the resin and to control its initial cure to the shaped solid below 200°C. This permits the phthalonitriles to be processed in the same way as ordinary commercial resins, using standard industrial composite manufacturing methods.

The PEEK-like phthalonitrile is a liquid above 70°C and polymerizes to a thermoset occurring above 150°C. The rate of polymerization is controlled as a function of temperature and the amount of curing additive, and the fully cured phthalonitrile polymer does not melt or soften when post-cured to temperatures greater than 375°C. NRL's phthalonitrile resins/prepolymers or resin prepregs have an indefinite shelf life without the need for refrigeration.

This story is reprinted from material from NRL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.