Synthesis And Application Of A New Phosphorus-Containing Silicon Flame Retardant

Polyethylene terephthalate(PET)is widely used in various fields because of its excellent mechanical properties,stable chemical properties and low cost.PET is used in automobile parts,electronic and electrical components,food containers and other fields,but its safety performance needs to be improved,and these fields put forward very strict requirements for the flame retardant performance of PET.Developing new flame retardants with low toxicity and good flame retardancy is currently one of the research directions for flame retardants.Organic phosphorus with the spiral ring structure takes more attention due to its rigid structure and high phosphorus content.In this paper,two new macromolecular phosphorus-silicon flame retardants were designed and synthesized,and their thermal stability was studied.They were applied to PET,and their flame retardancy,combustion behavior and thermal stability were investigated.The main research contents are as follows:1.A novel polymer phosphorus silicon flame retardant SPDPC-MVC with a network structure was synthesized using 2,4,8,10-tetraoxa-3,9-diphosphosporo[5.5]undecano-3,9-dioxide(SPDPC-H)and 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane(MVC)as raw materials.The chemical structure was characterized by infrared and nuclear magnetic resonance(NMR)spectroscopy,and its thermal stability was studied by thermogravimetry(TG)and differential scanning calorimetry(DSC).It was found that its initial decomposition temperature was 346.09℃,and the carbon residue rate at 800℃ was 18.13%.The flame retardant performance of SPDPC-MVC/PET material can reach UL-94 V-0 level and the limiting oxygen index can reach 27.5%,when the addition amount of SPDPC-MVC reaches 7%(w)in PET.The results of the cone calorimetry experiment showed that compared with pure PET,the heat release rate(HRR)and total heat release(THR)of the 10%PDPC-MVC/PET system decreased by 49.15% and 34.87% respectively.The smoke release rate(SPR)remained basically unchanged,while the total smoke release(TSP)decreased by 32.85% and the combustion intensity significantly decreased.At the same time,the morphology of residual carbon after combustion was analyzed.PET with 10%(w)SPDPC-MVC added showed many closed small pores on the surface after combustion,indicating that flame-retardant PET will release non combustible gas to dilute oxygen concentration during combustion,and also generate a carbon layer to isolate heat and air transfer.This indicates that flame retardants can exhibit flame retardancy in both gas and condensed phases,with excellent flame retardancy.When the addition amount is 7%(w),the mechanical properties of the composites are slightly reduced,the tensile strength is reduced by 7.71%,the elongation at break is reduced by 6.60% and the impact strength is reduced by 2.71%.Combined with the analysis of the flame retardant properties of the composites,it can be seen that when the amount of flame retardant is 7%(w),the flame retardant effect is excellent and the mechanical properties change little.2.A novel chain like intumescent flame retardant SPDPC-MSDS was synthesized from SPDPC-H and tetramethyldivinyl-disiloxane(MSDS),and its structure was characterized by infrared and NMR spectroscopy.The TGA and DSC results indicate that the thermal stability of SPDPC-MSDS is good,and a large amount of decomposition begins after 341.74℃.The residual carbon rate reaches 34.87% at 800℃.The initial decomposition temperature of SPDPC-MSDS/PET system was reduced by 53.07℃ compared to pure PET due to the preferential cleavage of P-O bonds in the flame retardant.However,the residual carbon rate increased to 20.10% at 800℃,indicating that SPDPC-MSDS contributes to the formation of the carbon layer and has good thermal stability.When the addition amount of flame retardant SPDPC-MSDS is 5%(w),the flame retardancy of SPDPC-MSDS/PET material can reach UL-94 V-0 level,and the LOI value can be increased to 28.5%,indicating good flame retardancy.The cone calorimetry results showed that compared with pure PET,the HRR of the 10% SPDPC-MSDS/PET system decreased by 44.17%,THR decreased by 30.13%,SPR remained basically unchanged,and TSP decreased by 24.41%.This indicates that the flame retardant mainly acts as a flame retardant in the condensed phase,forming a very dense carbon layer surface with fewer pores,which can block the transfer of air and heat,enhance the carbonization effect of PET during thermal degradation,and have a good flame retardant effect.When the dosage is 5%(w),the mechanical properties of the composites are slightly reduced,and the tensile strength,elongation at break and impact strength are reduced by 8.70%,8.15% and 4.34% respectively.Combined with the analysis of the flame retardant properties of the composites,when the amount of flame retardant is 5%(w),the flame retardant effect is excellent and the mechanical properties change little.