Preparation Of Phosphorus-Containing Schiff Bases And Their Derived Flame Retardants And Their Application In Epoxy Resins

Epoxy resin is widely used in various industrial fields because of its good mechanical,heat and chemical corrosion resistance.Epoxy resin is a flammable material,and the addition of flame retardants can effectively improve the flame retardant properties of epoxy resin.As people pay more attention to environmental protection,green flame retardants have become the development trend.The preparation of epoxy resin flame retardants from bio-based raw materials can expand the application of bio-based raw materials in the field of flame retardants.In this paper,bio-based flame retardants with higher flame retardant efficiency were prepared using bio-based vanillin as raw material and applied to epoxy resin,and the main research results are as follows:（1）A vanillin-based phosphorus-containing Schiff base flame retardant PH-VAN-AP was prepared by phenyl phosphoryl dichloride,vanillin and 4-aminophenol.The structure of PH-VAN-AP was characterized by FT-IR,H¹NMR and P³¹NMR.The flame retardant properties of epoxy resin（EP）were analyzed by vertical burning,limiting oxygen index and cone carlorimeter tests.The thermal stability and glass transition temperature（T_g）of EP were analyzed by TG and DSC tests.PH-VAN-AP was able to inhibit dripping and smoke generation of EP because it played the flame-retardant role in gas phase and condensed phase.The loading of 5 wt%PH-VAN-AP made the LOI value of pure EP increased from24.7%to 35.4%,and the peak heat release rate,total heat release and total smoke production of pure EP reduced by 165 k W/m²,5 MJ/m²and 1.2 m²,respectively,and increased its residual amount by 9.6 wt%.PH-VAN-AP could improve the T_gof EP,the T_gof EP with 5 wt%PH-VAN-AP increased from 156.9℃to 162.9℃.（2）A vanillin-based high-efficiency phosphorus and nitrogen synergistic flame retardant named PVAD was prepared from phenylphosphonlc dichloride,vanillin,3-amino-1,2,4-triazole and 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide（DOPO）.The structure of PVAD was characterized by FT-IR,H¹NMR and P³¹NMR.Flame retardant epoxy resins with 1 wt%,2 wt%and 3 wt%additions were prepared using PVAD.After testing,with only 1 wt%addition,the epoxy resin EP-1 can pass the V-0 level of the vertical combustion test standard（UL-94）with a LOI of 30.3%.The cone calorimetric test results showed that the PHHR and THR of EP-3 decreased by 22.9%and 7.9%,respectively,indicating that the introduction of PVAD could improve the flame retardancy of the epoxy resin.PVAD was able to increase the T_gof epoxy resin,and the addition of 2 wt%increased the T_gof epoxy resin from 150.3℃to 159.8℃.PVAD/EP samples were tested and their bending strength and tensile strength were enhanced,and the bending strength of EP-3increased by 10.9%,tensile strength increased by 8.2%,and tensile elongation at break increased from 7.05%to 9.93%.This indicates that PVAD has a strengthening and toughening effect on the epoxy resin.（3）DOPO was compounded with the pre-synthesized PH-VAN-AP and introduced into the epoxy resin.With a total addition of 3 wt%,the epoxy resin EP-PH/DOPO-3 can pass the UL-94 V-0 level with a LOI of 34.8%.The cone calorimetric test results showed that the PHR and THR of EP-PH/DOPO-3 were reduced by 16.3%and 10.3%,respectively,and increased the residual amount by 6.8%.Compared with the epoxy resin with only DOPO added,the compounding of PH-VAN-AP with DOPO improved the carbon formation ability of the epoxy resin,and improved the adverse effect of DOPO on the heat resistance performance of the epoxy resin.