Research On Preparation And Properties Of Phosphorus-silicon Synergistic Flame Retardant Nylon 66

Nylon 66,namely polyamide6,6?PA66?,is the most consumed thermoplastic resin in general engineering plastics.It has excellent mechanical properties and can be widely used in aviation,automobile,machinery,electronics,chemical industry,construction and other fields.The ultimate oxygen index of PA66 is 24%,and the vertical combustion performance of UL-94 reaches to V-2 level,which means PA66 is possessed with certain flame retardancy.However,with the expansion of application field,its flame retardant performance can not meet the more stringent environmental requirements.It is imperative to improve the flame retardant performance of PA66.Halogen-containing flame retardants are equipped with high flame retardant efficiency,but they will lead to the environmental pollution.There are few kinds of phosphorus-or nitrogen-based flame retardants suitable for PA66 because of its higher processing temperature.Therefore,there is a great significance to develop new halogen-free flame retardants.In this paper,based on the higherprocessingtemperatureofPA66resin,thereactionintermediate,1-oxo-4-hydroxymethyl-2,6,7-trioxa-l-phosphabicyclo[2.2.2]octane?PEPA?was synthesized with phosphorus oxychloride and pentaerythritol,then a organic phosphorus flame retardant owed with high symmetrical and high decomposition temperature,phenyl-dual-?1-oxo-phosphorus hetero-4-hydroxymethyl-2,6,7-trioxa hetero-bicyclic[2.2.2]octane?-oxo-phosphonic?BPEPA?was obtained by the reaction of PEPA with phenylphosphatidyl dichloride.Finally,BPEPA and nano-SiO₂ were added to PA66 resin to prepare flame retardant PA66 materials,and the thermal properties,mechanical properties and flame retardant properties of the materials were measured,the main conclusions are as follows:?1?PEPA,the intermediate of flame retardant,was synthesized by using phosphorus oxychloride and pentaerythrotol as raw materials,1.4-dioxane as solvent.BPEPA,the final product of flame retardant,was obtained by through the reaction of PEPA with phenylphosphatidyl dichloride with triethylamine as acid binding agent,and acetonitrile as solvent.Fourier transform infrared?FTIR?and nuclear magnetic resonance?NMR?results showed that the target product has been successfully synthesized.The results of thermal stability test?TGA?showed that the initial decomposition temperature?T_i?of PEPA and BPEPA was 284.6?,354.1?,the temperature of maximum mass loss rate(T_max)was298.7?,368.7?,and the carbon residue at 600?was 48.23%,46.35%,respectively.?2?Flame retardant PA66 was prepared by adding BPEPA to PA66 matrix via single factor experiment method,and its thermal,mechanical and flame retardant properties were measured.The results of thermal performance test showed that the melting point?T_m?,crystallization temperature?T_c?and initial decomposition temperature of PA66 were decreased,the storage modulus and loss factor were increased,respectively,and the carbon residue rate at 600?was increased.The results of mechanical properties test showed that the tensile strength,flexural strength and impact strength of PA66 were continuously decreased,when adding 20wt%BPEPA,the three strengths were decreased by 15.8%,13.9%and 16.9%respectively compared with pure PA66.The flame retardancy test showed that the LOI increased from 24%of pure PA66 to 26.9%with the addition of20wt%BPEPA,and the vertical combustion performance of UL-94 reached to V-1.?3?The BPEPA/nano-SiO₂/PA66 was prepared by fixing the amount of BPEPA20wt%and changing the amount of nano-SiO₂.The thermal,mechanical and flame retardant properties of the material were measured.The results of thermal performance test showed that the T_m and T_c of PA66 were decreased slightly after adding nano-SiO₂,the T_i was delayed,and the storage modulus and loss factor were still increased.The results of mechanical properties test showed that the tensile strength,flexural strength and impact strength were increased firstly and then decreased.When the nano-SiO₂ content was 4wt%,the three strengths were decreased by 13.3%,12.6%and 18.2%respectively compared with pure PA66.The flame retardancy test results showed that flame retardant,BPEPA and nano-SiO₂,could improve the combustion performance of PA66.When BPEPA content was 20wt%and nano-SiO₂ was 4wt%,LOI increased from 24%of pure PA66 to 27.6%,but vertical combustion performance was still V-1.The peak heat release rate?pHRR?,total heat release?THR?,total smoke release?TSP?of pure PA66 was 645.49kW/m²,94.23MJ/m²and 9.12m²/kg,decreased to 588.13kW/m²,80.06MJ/m²and 8.37m²/kg respectively,and the mass loss was increased from 1.61g to 2.32g.