Synthesis Of Halogen-Free Phosphorus Flame Retardant And Preparation And Properties Of Flame Retardant Epoxy Resin Materials

Bisphenol A diglycidyl ether type epoxy resin?DGEBA?has a large production volume and is widely used.Due to the flammability and brittleness of DGEBA thermosets,the development of flame retardant modified DGEBA is of great significance for its application and development.In recent years,Although many advances have been made in the synthesis of flame retardant epoxy resin,flame retardant curing agent,nano flame retardant and its flame retardant properties,flame retardant mechanism and the kinetics of the curing process,little research has been done on the structural characteristics of DGEBA and diisocyanate-modified DGEBA?DI-DGEBA?to design high-efficiency phosphorus-based flame retardants.In this study,three kinds of new high-efficiency phosphorus-based flame retardant?NFRP?were designed and synthesized,The research ideas include:?1?Which contain a rigid 9,10-dihydro-9-oxo-10-phosphaphenanthrene-10-oxide?DOPO?group in the+1 valence state and a flexible phenylphosphonate group in the+3 valence state,and aroma that can form hydrogen bonds with hydroxyl groups,which improve NFRP flame retardant efficiency and compatibility.?2?By microscopic interaction between NFRP and DGEBA,including dipole-dipole action due to thermal activity to improve material properties.Finally the flame retardant properties,fire hazard,DMA,thermal performance and flame retardant mechanism of flame retardant DGEBA and DI-DGEBA thermosets which based on NFRP and the composite of NFRP and aluminum oxide?Al₂O₃?were studied in detail.Main research contents and results as follows:?1?Three kinds of NFRP containing+1 valent phosphorus and+3 valence phosphorus were synthesized by esterification,nucleophilic addition and substitution reactions by using phenylphosphoryl dichloride?BPOD?,p-hydroxybenzaldehyde?PHB?,DOPO,4,4'-diaminodiphenylmethane?DDM?,m-phenylenediamine?mPDA?,and melamine?ML?,etc.The difference about these NFRP structures are that contained DDM?DOP-DDM?,mPDA?DOP-mPDA?and ML?DOP-MA?groups,respectively.And the structure of NFRP was characterized by FTIR and NMR(¹H NMR,¹³C NMR and ³¹P NMR).NFRP flame retardant DGEBA and DI-DGEBA thermosets were prepared by using DOP-DDM,DOP-mPDA and DOP-MA as flame retardant additives and DDM as curing agent.At the same time,DOP-DDM composite metal oxide flame retardant DGEBA and DI-DGEBA thermosets were prepared by combining DOP-DDM with Al₂O₃,montmorillonite?MMT?,CuO and their mixtures.?2?The transmittance of NFRP flame retardant DGEBA thermosets was tested by UV-Vis spectrometer.The results showed that only the DOP-DDM flame retardant DGEBA thermosets has good transparency in the visible range.Even the DOP-DDM was added to 7.6wt.%,the transmittance of the 1 mm thick DOP-DDM flame retardant DGEBA thermosets can reach to96.2%relative Neat EP.The results of LOI and UL-94 indicate that DOP-DDM,DOP-mPDA and DOP-MA were added in the amount of 4.7wt.%?wt means the mass percentage?,the LOI values of the flame retardant DGEBA thermosets were 33.5%,33.4%and 33.8%,respectively.And both achieved UL-94 V-0.The flame retardant efficiency of the NFRP flame retardant DGEBA thermosets was evaluated as follows:DOP-DDM>DOP-MA>DOP-mPDA.Among them,the phosphorus content in the DOP-DDM flame retardant DGEBA thermosets was only0.369wt.%.DSC analysis showed that the DOP-DDM flame retardant DGEBA thermosets had the same T_g as the Neat DGEBA thermosets.The results of DMA showed that the storage modulus?E??and loss modulus?E???of DOP-DDM flame retardant DGEBA thermosets was increased by 65.7%and 47.3%,respectively.?3?The LOI of DOP-DDM?3.2wt.%?composite Al₂O₃?1.0wt.%?and MMT?0.5wt.%?and DOP-DDM?3.2wt.%?composite Al₂O₃?0.5wt.%?and CuO?0.5wt.%?flame retardant DGEBA curing are 33.2%and 33.5%,respectively.All of them can achieve UL-94 V-0.The results of cone calorimetry showed that DOP-DDM and Al₂O₃ and CuO composite,compared with Neat DGEBA thermosets,the former p-HRR and THR decreased by 22.6%and 57.5%,respectively.SPR and TSR decreased by 9.6%and 7.3%,respectively.And CO and CO₂ release rates decreased by 11.5%and 39.1%,respectively.DSC analysis showed that the T_g of DOP-DDM composite Al₂O₃ and CuO flame retardant DGEBA thermosets increased by 7°C.The results of DMA showed that the storage modulus?E??and loss modulus?E???of DOP-DDM composite Al₂O₃ and CuO flame retardant DGEBA thermosets increased by 37.7%and 10.8%,respectively.?4?Diisocyanate modified epoxy resins MDI-DGEBA and HDI-DGEBA were synthesized through the reaction of hydroxyl groups in DGEBA molecular chain with MDI and HDI respectively.And flame retardant DI-DGEBA curing were prepared by using DOP-DDM,DOP-mPDA,DOP-MA and metal oxide as single and composite flame retardant additives and DDM as curing agent.Formulation control experiments showed that the HDI-DGEBA curing had a LOI value of 30.4%when the molar ratio of DGEBA to HDI was 5:1,and it passed UL-94 V-1.The results of DMA analysis showed that the storage modulus?E??and loss modulus?E???of the HDI-DGEBA curing were 65.1%and 32.4%higher than that of the Neat DGEBA curing,respectively.The LOI of flame retardant HDI-DGEBA curing that was prepared by DOP-DDM?5.8wt.%?composite Al₂O₃?0.5wt.%?and CuO?0.5wt.%?was 33.1%,and it can reach UL-94 V-0.Compared with Neat DGEBA curing,the p-HRR and THR of the flame retardant HDI-DGEBA curing decreased by 17.6%and 12.6%,respectively,SPR and TSR decreased by 12.5%and 12.6%,respectively,and the CO and CO2 release rates were reduced by 32.3%and 18.3%,respectively.The flame retardant HDI-DGEBA curing has the same T_g as the Neat DGEBA.And compared with Neat DGEBA curing,the storage modulus?E??and loss modulus?E???of flame retardant HDI-DGEBA curing increased by 54.2%and 22.3%,respectively.?5?For flame retardant DGEBA thermosets,the mechanism was mainly based on gas phase flame retardant mechanism.The thermal weight loss process was analyzed by TGA,the gas phase components was analyzed by TGA-FTIR,and the main functional groups of residual carbon,degree of graphene and SEM residual carbon morphology were analyzed by FTIR and Raman spectroscopy.Since Al₂O₃ can improve the barrier properties of carbon residue,CuO can inhibit the release of CO and CO₂.Therefore,the composite flame retardant systems of NFRP,Al₂O₃ and CuO have the best synergistic flame retardant and smoke suppressing properties,which can improve the flame retardancy of condensed phase.Sothe amount of the organic flame retardant is reduced,and the flame retardancy and fire safety are improved.