Flame retardant strategies for the synthesis of hybrid epoxy nanocomposites

A combination of different hybrid strategies exploited in the flame retardation of bisphenol A diglycidyl ether (DGEBA) resin cured with a cycloapliphatic amine, namely isophorone diamine, is presented. First, epoxy nanocomposites were prepared through an in-situ sol–gel procedure for the modification of DGEBA resin with silanes. Hence, inorganic-organic hybrid structures were obtained, containing silica nanocrystals chemically bonded to the epoxy chains. Then, flame-retardant silica-epoxy materials were synthesized by incorporating two phosphorus-based flame-retardant additives (non-toxic DOPO derivatives) together with melamine as a nitrogen additive, followed by curing with isophorone diamine. The hybrid strategy allowed for achieving self-extinction (V0 rating in UL 94 test) for both systems with only 2 wt.% of P loading. Promising fire performances were also achieved by embedding phosphorus in the silica-based nanostructures using phosphoric acid through a hydrolytic sol-gel procedure. A similar synthetic approach was also effective in the formation of magnesium hydroxide nanocrystals in the epoxy matrix. The fire behavior of this system was experimentally studied and predicted by applying a machine learning method.