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At present, most halogen-free materials are mainly phosphorus and phosphorus nitrogen systems. When the phosphorus containing resin is burned, it will decompose to generate metapolyphosphoric acid, which is highly dehydrated, making the surface of the polymer resin form a carbonized film, isolating the burning surface of the resin from the touch of the air, calming the fire and achieving the flame retardant effect. The high molecular resin containing phosphorus and nitrogen compounds can produce non combustible gas when burning, helping the resin system to be flame retardant.