Synthesis Of DOPO Derivative Flame Retardant And Study On Its Copolymerized Flame Retardant PA66

Polyamide66(PA66)is a material with good wear resistance,high strength,and high impact toughness.It has been widely used in textile,construction,automobile industry and other fields.However,fire safety is a major concern in these fields,as PA66 is a combustible substance that produces melting drops and smoke when burned.Therefore,modifying the flame retardant of PA66 material is of great significance.This paper aims to overcome the problems of existing additive and reactive flame retardant PA66,such as high addition amount,negative effects on mechanical and processing properties,and poor heat resistance.A novel flame retardant DDPCA was synthesized by reacting itaconic acid(ITA),HMDA,9,10-dihydro-9-oxa-10-phospho xanthine-10-oxide(DOPO)and calcium hydroxide(Ca(OH)2).The influences of temperature control,calcium hydroxide addition,reaction time,and washing times on the yield and purity of DDPCA flame retardant were investigated.The optimal reaction conditions were obtained.The structures of flame retardants were characterized by FTIR,Raman,SEM,EDS and thermogravimetric test.The flame-retardant polyamide 66(FRPA66)material was synthesized by reaction copolymerization of DDPCA and PA66 salt in a high-pressure reactor.The optimal copolymerization conditions of DDPCA-modified PA66 were determined by varying the salt solution concentration and the vacuum holding time.The structure of FRPA66 was characterized by FTIR,NMR,viscosity test,EDS and XRD.The effects of DDPCA flame retardant content on the thermal stability,non-isothermal crystallization kinetics,flame retardancy,combustion and mechanical properties of FRPA66 were also investigated.The main results are as follows:(1)The synthesis of DDPCA,a DOPO derivative flame retardant,was confirmed by FTIR,Raman and EDS Mapping results.The optimal synthesis conditions were:water bath temperature of 85℃,calcium hydroxide amount of 0.54 mol,reaction time of 150min after adding calcium hydroxide powder,and washing times of flame retardant powder of 4 times.The DDPCA had an initial thermal degradation temperature of 231℃,a maximum thermal degradation temperature of 348℃,and a residual carbon rate of 8.63%after decomposition.(2)The synthesis of FRPA66 material was confirmed by FTIR and ~1H NMR spectroscopy tests.The optimal synthesis conditions were:salt solution concentration of50wt%,and vacuum time of 5 min in the polymerization reactor.The FRPA66-6 had a relative viscosity of 2.48 and a phosphorus content of 0.366wt%.XRD analysis results show that the crystallite size,crystal planar spacing and crystallization density of FRPA66decrease with the increase of DDPCA flame retardant content,and the crystal form of FRPA66 changes fromγtoαafter isothermal crystallization.(3)The DSC test results showed that the DDPCA flame retardant reduced the melting temperature,crystallization temperature and crystallinity of PA66,but less than the DDP-FRPA66 with the same amount.The non-isothermal crystallization kinetics analysis of PA66 and FRPA66 showed that the DDPCA flame retardant lowered the initial crystallization temperature,widened the crystallization temperature range,shortened the semi-crystallization time T1/2,and decreased the crystallization rate of PA66.The thermogravimetric analysis results showed that:The DDPCA flame retardant lowered the initial thermal degradation temperature of PA66,but increased the residual carbon rate and the termination thermal degradation temperature.The FRPA66-6 had a termination thermal degradation temperature of 497.6℃,a residual carbon rate of 5.73%,and a dense residual carbon layer,indicating that the DDPCA flame retardant had a condensed phase flame retardant effect.(4)The LOI value of FRPA66 increased with the increase of DDPCA flame retardant content.The FRPA66-6 had a LOI value of 27.2%,indicating a refractory material.The FRPA66-4 and FRPA66-6 achieved a V-0 level in vertical combustion test.In cone calorimetry test,the FRPA66 showed a significant reduction in the maximum heat release rate and the total heat release,and an increase in the fire performance index and the CO and CO2 release with the increase of DDPCA flame retardant content.The FRPA66-6had a maximum heat release rate of 271 k W/m~2,a total heat release of 78 MJ/m~2,a fire performance index of 0.276 s·m~2/k W,a CO release of 57.6 g/kg,and a CO2 release of1036 g/kg,compared to pure PA66 with 1015 k W/m~2,105 MJ/m~2,0.142 s·m~2/k W,16.8g/kg,and 752 g/kg respectively.The smoke release of FRPA66-6 was much higher than that of pure PA66(3442 m~2/m~2 vs 803 m~2/m~2).The residual carbon rate of FRPA66-6was 7.51wt%,while that of pure PA66 was only 2.85wt%.The SEM image of the residual carbon of FRPA66 confirmed that the DDPCA had a flame-retardant effect in both the gas phase and the condensed phase.(5)The test results of tensile performance,notched impact performance and bending performance show that the mechanical properties of FRPA66 decrease with the increase of DDPCA flame retardant.Compared with DDP-FRPA66,the mechanical properties of DDPCA copolymer flame retardant PA66 are improved.