Flame retardant epoxy resin composition

A method for making a flame retardant epoxy resin composition for fiber-reinforced composite material, the method comprising:

• combining a component [A] with a component [B] to form a component [A-1], followed by
• adding to the component [A-1] a thermoplastic resin selected from polyvinyl acetal resin, polyvinyl alcohol, phenoxy resin, polyamide, polyimide, polyvinyl pyrrolidone, polysulfone, or polyethersulfone, and kneading at 130° C. to 180° C. using a kneader, planetary mixer, three-roll mill, or twin-screw extruder until the thermoplastic resin dissolves in the component [A-1], followed by
• adding a component [C],
• wherein:
• the flame retardant epoxy resin composition has a phosphorus content of at least 0.5% by weight based on the total weight of the flame retardant epoxy resin composition;
• the flame retardant epoxy resin composition has a minimum viscosity of 0.1 to 200 poise, and the component [A] is comprised of at least one low total heat release (THR) multifunctional epoxy resin having a total heat release (THR) value of ≤23 KJ/g, wherein a total amount of low THR multifunctional epoxy resins is at least 15 PHR to 85 PHR;
• the flame retardant epoxy resin composition is comprised of at least one high THR multifunctional epoxy resin having a THR value of greater than 23 KJ/g;
• the component [A-1] is comprised of at least one low THR multifunctional epoxy resin that contains at least one residue of at least one organic phosphinic acid;
• the component [B] is comprised of at least one organic phosphinic acid;
• the component [C] is comprised of at least one curing agent;
• and
• the at least one low THR multifunctional epoxy resin is comprised of at least one epoxy resin having at least one glycidyl amino group and/or diglycidyl amino group.