Synthesis Of "Trinity" Reactive Flame Retardant And Study On Its Modified Pa66

Nylon 66(PA66)was a widely used engineering plastics,but its application range was limited by poor flame retardancy.At present,Intumescent flame retardant had high flame retardant efficiency because of the synergistic flame retardant effect of acid source,carbon source and gas source.However,its application in PA66 was mainly in the form of additives,which had a certain negative impact on the mechanical properties.At the same time,the introduction of reactive flame retardants has attracted much attention because of their excellent flame retardancy and little influence on mechanical properties.Therefore,this paper combined the advantages of the two methods,and developed a“trinity”reactive flame retardant to modify PA66.A“trinity”reactive flame retardant,4,4'-((3,9-dioxido-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane-3,9-diyl)bis(azanediyl))dibenzoic acid(DTDBA)was successfully synthesized from pentaerythritol,phosphorus oxychloride and p-aminobenzoic acid in two steps,and the optimum synthesis process was determined.FTIR,NMR,elemental analysis and TGA results showed that DTDBA had high purity.Its initial thermal decomposition temperature was 220?,and it would not decompose at the polymerization temperature of PA66(210?).The carbon residual rate was 18%when the temperature reached 600?.The intrinsic flame retardant PA66 was synthesized from DTDBA,hexamethylenediamine and PA66 salt by two steps,and its structure was characterized by FTIR.The results of performance study showed that LOI value,UL-94 grade and char formation rate of flame retardant PA66 increased with the increase of DTDBA content.When DTDBA salt content was 4wt%,the values were 30.5%,V-0grade and 11.75%,respectively.The values of T_m and T_g of flame retardant PA66 decreased with the increase of DTDBA content,but the initial decomposition temperature and maximum thermal decomposition temperature increased gradually,and the char residue rate increased significantly at550?,it showed that the addition of DTDBA improved the thermal stability of PA66.The addition of DTDBA has little effect on the mechanical properties of PA66,which could meet the practical application.Compared with the general phosphorus-nitrogen reactive flame retardant(DPTPO),this“trinity”reactive flame retardant(DTDBA)showed superior flame retardancy in flame retardant modification of PA66.The mechanism of DTDBA flame retardant PA66 was revealed by dynamic infrared analysis,micro-morphology analysis of carbon layer after combustion test and Raman spectroscopy analysis.P,N and high carbon polyhydroxy compounds produced by thermal decomposition of flame retardant PA66 could be used as acid source,gas source and carbon source respectively.The three sources played a synergistic role in the formation of an expandable,porous and dense non-flammable carbon layer on the combustion surface.The layer hindered the combustion reaction by isolating heat and oxygen exchange,thus realizing the synergistic flame retardant effect of condensed phase and gas phase.