Development of polyureas with improved fire resistance

Abstract

The demand for improved damage control materials to address high strain rate impact has led to exploration of polyureas in this role. Polyureas show potential for retrofitting pre-existing platforms because they can be applied as a spray and have extremely fast cure times and low volatile organic compounds. However, they have been limited in use in enclosed spaces because of their flammability. In this article, synthetic and additive routes to improve polyurea flame retardancy are systematically explored. The US Department of Defense test method standard Military Standard 2031 has been used as a target to meet or exceed for flammability properties. This article will outline the changes in polymer chemistry, the addition of fire-retardant additives, and the use of ignition barrier coatings that led to a composition that exceeded the military standard.

Formulation of polyurea with improved flame retardant properties

“…APP alone decreases the thermal stability of PU as consequence of the formation of phosphoric acid, which can act as a catalyst for PU degradation. 13 However, the other OP combinations did not improve the thermal stability. Poor thermal stability is observed in EG and A-78 combination, which may be attributed to the lower thermal stability of both additives.…”

“…Sulfur compounds are also used in polycarbonate. [10][11][12] Recently, Underhill et al 13 have reported the fire resistance of PU using three different routes, chemical modification, additives, and surface coating. In earlier work from this laboratory, the effect of almost 50 individual FRs, from every class of conventional FRs, was used to evaluate the flammability of PU; the most efficacious materials were expandable graphite (EG), ammonium polyphosphate (APP), aluminum diethylphosphinate (OP 1314), and melamine polyphosphate (MPP), evaluated based on the percentage reduction of the peak heat release rate (HRR) from cone calorimetry at a heat flux of 50 kW/m 2 .…”

Crystallizable and Tough Aliphatic Thermoplastic Polyureas Synthesized through a Nonisocyanate Route

“…Meanwhile, phosphorus-containing monomers can be used to synthesize phosphorus-containing PUreas with improved flame-retarding properties. 12 Diisocyanates are currently prepared from extremely toxic phosgene. Diisocyanates also show high toxicity.…”

“…PUUs are currently prepared from diisocyanates and polyols with diamines as chain extenders. − PUreas are prepared from diisocyanates and polyamines and are usually used as two-component systems in the protective coating/lining industry. − PUUs and PUreas normally exhibit better mechanical properties than common PUs because urea groups provide additional hydrogen bonds. Meanwhile, phosphorus-containing monomers can be used to synthesize phosphorus-containing PUreas with improved flame-retarding properties . Diisocyanates are currently prepared from extremely toxic phosgene.…”