▎ 摘　　要

NOVELTY - Phosphorus-nitrogen-silicon composite intumescent flame retardant is prepared by reacting nitrogen source and silicon source, and reacting with phosphorus source, where the nitrogen source is melamine, urea, melamine cyanuric acid, and/or melamine polyphosphate. The silicon source is methylvinyldichlorosilane, ethylvinyldichlorosilane, methacryldichlorosilane, and/or (glycidyloxy)-propylmethyldichlorosilane. The phosphorus source is 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. USE - The phosphorus-nitrogen-silicon composite intumescent flame retardant is useful for preparing epoxy resin, polyethylene glycol terephthalate or polylactic acid. ADVANTAGE - The phosphorus-nitrogen-silicon composite intumescent flame retardant has good flame-retardant effect, improves limit oxygen index and vertical combustion performance of polymer, prolongs time for polymer to reach heat release rate peak value, and improves polymer flame retardance. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: a method for preparing phosphorus-nitrogen-silicon composite intumescent flame retardant comprising (1) polymerizing and washing nitrogen source solution and silicon source solution to obtain an intermediate product, (2) reacting intermediate product with phosphorus source in solvent in presence of the initiator, and cooling to obtain phosphorus-nitrogen-silicon composite intumescent flame retardant, optionally (3) reacting graphene oxide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 4-dimethylaminopyridine and phosphorus-nitrogen-silicon composite expansion flame retardant to obtain phosphorus-nitrogen-silicon composite intumescent flame retardant grafted with graphene oxide; and a flame retardant epoxy resin comprising phosphorus-nitrogen-silicon composite expansion flame retardant, where the mass ratio of phosphorus-nitrogen-silicon composite intumescent flame retardant to epoxy resin is 0.001-0.3:1.