Phosphorus-based triazine compound endowing epoxy thermosets with excellent flame retardancy and enhanced mechanical stiffness

Abstract

Searching highly-efficient flame retardants for flame-resistance and smoke-suppressed epoxy thermosets with enhanced mechanical performance has aroused considerable interest in the field of flame-retardant materials. Herein, a phosphorus-based flame retardant, 6,6′,6''-(1,3,5-triazine-2,4,6-triyl)tris(oxy))tris(3-methoxybenzene-4,1-diyl))tris(hydroxymethylene))tris(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (Trif-D), was synthesized using a two-step method and served as the flame-retardant additive for commercial epoxy thermoset. The epoxy thermoset with the low loading of 5.0 wt% Trif-D (Trif-D-5, phosphorus content = 0.39 wt %) possessed a UL-94 V-0 rating (with a limiting oxygen index of 33.1%). According to the cone calorimeter test, compared with epoxy thermoset without Trif-D addition (Trif-D-0), the reductions of peak heat release rate and total smoke production in Trif-D-5 were 66.3% and 51.3%, respectively. The mechanism analysis confirmed that the phosphorus-based structure from Trif-D contributed both the gaseous-phase and condensed-phase flame retardance of epoxy network. Moreover, Trif-D-5 possessed the high mechanical stiffness due to the introduction of rigid structures (phosphaphenanthrene, triazine and benzene) from Trif-D, showing 5.2%, 3.6% and 5.9% increase in storage modulus (at 30 °C) (3.03 GPa vs. 2.88 GPa), tensile modulus (3.47 GPa vs. 3.35 GPa) and flexural modulus (2.89 GPa vs. 2.73 GPa) as compared to Trif-D-0, respectively. The present paper investigates a facile method for the fabrication of high-performance epoxy thermosets with excellent flame retardance and enhanced mechanical stiffness.