Semi–interpenetrating networks based on epoxy resin and oligophosphonate: Comparative effect of three hardeners on the thermal and fire properties

Traditional materials are being constantly replaced by synthetic polymers, most of which are highly flammable. Epoxy resins are versatile and among the most important class of polymers, due to their multiple crosslinking capacity endowed by the oxirane ring, their applications ranging from adhesives to aeronautics. This study investigates the comparative effect of three hardeners (aromatic, cycloaliphatic, aliphatic) and the addition of an oligophosphonate on the thermal behavior and fire performance of bisphenol A diglycidyl ether semi–interpenetrating polymer networks. Networks with epoxy resin and 2% phosphorus loading were prepared. Evolved gases analyses, thermal and fire experiments were used to propose the action mode of the hardeners and oligophosphonate in the fire performance enhancement of the epoxy resin. Non–isothermal decomposition kinetics studies were conducted. The oligophosphonate in the epoxy resins promoted a significant reduction in the peak of heat release rate values (33 to 55%) in microscale combustion calorimeter experiments. A UL 94–V0 classification was achieved for the network with oligophosphonate and aromatic curing agent. The obtained results recommend the semi–interpenetrating network cured with aromatic hardener as a potential matrix for flame retardant composites or coatings.