Study On The Synthesis Of Phosphorus-containing Flame Retardant Copolyamide66and Its Properties

Polyamide66(PA66)，with good mechanical properties, outstanding chemicalstability and easy processing performance, has been widely used in the industry ofautomotive, chemical, textile and electronic. However, the flammability of PA66limits its application in some specific areas. So it becomes one of the hottest researchspot in the industry of PA66to improve the flame retardancy of PA66. Meaningfulachievements on the research of flame retardant PA66have been made by the effortsof scholars at home and abroad, but those studies mainly focused on physicalmodification or surface grafting. In addition, only few researches were reported aboutthe copolymerization flame retardant modification of PA66.In this article,2-Carboxyethyl(phenyl)phosphinic acid (CEPPA) was synthesizedthrough a two-step process, and optimal CEPPA–HMD was acquired by pretreating itwith hexamethylene diamine (HMD). Then flame retardant PA66(FR–PA66) wasprepared through copolymerization in which the optimal CEPPA–HMD monomer wasintroduced into the macromolecular chain of PA66. The structures of flame retardantCEPPA, flame retardant monomer CEPPA–HMD and copolymerization productFR-PA66were characterized. The synthesis process of FR–PA66was explored andmodified. The effect of flame retardant on the crystallization, melting behavior,thermal stability and flame retardancy of FR-PA66were also researched.The results showed that:(1) the synthesized flame retardant contained themolecular structure of CEPPA, and the flame retardant monomer CEPPA–HMD wasacquired by the reaction between–COOH on CEPPA and–NH2on HMD throughpretreatment. As a result, the initial decomposition temperature increased to286℃,and the content of residual char at600℃increased significantly;(2) The productobtained by copolymerization exhibited structure characteristics of both PA66macromolecular and phosphorus-containing flame retardant, and the content ofphosphorus in FR–PA66samples increased with the increasing of the adding amount of flame retardant, so did the difficulty of copolymerization reaction, therefore ahigher reaction temperature and longer reaction time were needed;(3) Theintroduction of flame retardant structure didn’t change the crystal structure andmultiple melting behavior of PA66, but it lowered the growth rate of crystal and led tosmaller size, incomplete crystallization, and the melting point decreased as the flameretardant increased;(4) The introduction of flame retardant changed the thermaldecomposition of PA66, and promoted the char formation, and the LOI valueincreased with the increasing of flame retardant, which has effectively improved theflame retardancy of PA66.