A facile crosslinking strategy endows the traditional additive flame retardant with enormous flame retardancy improvement

With great chemical and physical properties, epoxy resins (EPs) are used almost everywhere in life and engineering, but poor flame-retardant performance hinders them for a wider use. Traditional flame retardants (the most commonly used and researched) usually have dispersion and migration problems (additive ones) or are difficult to synthesize (reactive ones). Herein, a facile crosslinking strategy is used to make traditional additive flame retardants exhibit much better properties. Firstly, a nitrogen/phosphorus containing additive flame retardant with nitrile groups is designed, successfully synthesized, and directly mixed with EP matrix, the secondary crosslinking reaction of nitrile groups inner the flame retardants will occur in cured EP thermosets which was driven by a facile thermal treatment procedure. Then the properties of the flame retardant mixed and crosslinked EP composites are measured by limiting oxygen index (LOI) test, thermogravimetric analyses (TG), UL-94 vertical burning tests, dynamic mechanical analysis and cone calorimeter test, the results show that the crosslink of the additive flame retardant greatly improved the flame-retardant properties, and with 20 wt% loading content of the crosslinked flame retardant, the LOI value reach 46.2% and the peak heat release rate decreases for 77.4% compared with neat EP, furthermore the heat resistance and dynamic mechanical property of the crosslinked samples also get promoted compared with the physical mixed ones.