Synthesis Of Organophosphorus And Boron Hybrid Flame Retardant And Its Application In Epoxy Resin

Epoxy resin(EP)is a kind of common polymer,which is widely used in various fields because of its excellent comprehensive properties.However,due to the flammability of epoxy resin,there are potential safety risks during its use,which limits the expansion of its application space.Therefore,The introduction of flame retardant into epoxy resin to improve its fire safety performance is an important research content in this field.Flame retardants with characters of non-halogen,lower poison and green sustainable have been the basic principle of flame retardant design today,and the multi-element synergistic flame retardants have been paid much attention to because of its high flame retardant efficiency.Therefore,based on the phosphorus-boron synergistic flame retardant effect,this paper designs and synthesizes two types of organophosphorus/boron hybrid flame retardant with good compatibility and high flame retardant efficiency,one containing monophenylboronic acid group abbreviated as DPC-1B,the other abbreviated as PDS-2B which containing diphenylboronic acid group.This article mainly explores the effects of the transparency,mechanical properties and flame retardant properties after two flame retardants being introduced into the epoxy resin,preliminary discusses the flame retardant mechanism of DPC-1B and PDS-2B,and explores the difference between the two flame retardants on the properties of epoxy resin.(1)Using 4-hydroxyphenylboronic acid(HPB)as boron source,diphenylhypophosphosyl chloride(DPC)or phenylphosphosyl dichloride(PDS)as phosphorus source,flame retardants DPC-1B and PDS-2B were obtained by one-step reaction,two kinds of synthesis reactions are simple and quick,and the post-treatment method is easy and convenient operation.FT-IR and NMR spectra(1H NMR,31P NMR,13C NMR)were used to characterize the structures of the two kinds of flame retardants,The thermal stability of the two kinds of flame retardants was characterized by TGA.(2)DPC-1B and PDS-2B were introduced into the epoxy resin prepolymer to prepare epoxy resin composites,and diphenylphosphoric acid,4-hydroxyphenylboric acid,diphenylphosphoric acid and 4-hydroxyphenylboric acid blends were added into the epoxy resin prepolymer to prepare epoxy resin curable materials as the control group.DSC test shows that both DPC-1B and PDS-2B can react with epoxy resin matrix,participate in the curing behavior of epoxy resin and have good compatibility with epoxy resin,retaining the high transparency of epoxy resin.DMA test and three point bending mechanics test show that both DPC-1B and PDS-2B can improve the mechanical properties of epoxy resin composites.According to TGA data,the epoxy resin cured with two flame retardants has a lower maximum thermal decomposition rate and a higher carbon residue rate.In the flame retardant test,compared with the control group,the addition of DPC-1B and PDS-2B made the epoxy resin composite have higher LOI value and higher UL-94 grade compared with the addition of a single raw material.The LOI value of the epoxy resin added with 2%DPC-1B reached 31.8%.The LOI value of the epoxy resin with 2%PDS-2B was 31.5%,while the epoxy resin with 1%DPC-1B and 2%PDS-2B reached UL-94 V 0 grade.By cone calorimetry test,it was found that the total heat release and the maximum heat release rate of epoxy resin could be reduced when the addition amount of DPC-1B and PDS-2B was low.The peak heat release rate decreased by 26.5%and 21.8%,respectively,when the two flame retardants were added only 2%,and it was found that PDS-2B had a better inhibition effect on smoke than DPC-1B.(3)TG-FTIR test showed that PDS-2B epoxy resin composites produced less CO2,the addition of two flame retardants could limit the production of gas phase products,and well inhibit the appearance of carboxyl compounds.The epoxy resin carbon residue was more tight and continuous after the addition of two flame retardants,while the carbon residue of PDS-2B epoxy resin composite was more dense and expanded than the carbon residue of DPC-1B epoxy resin composite.This carbon layer structure can effectively block the transfer of heat so that the internal polymer is not easy to burn.Raman spectrum analysis shows that compared with DPC-1B,PDS-2B can improve the graphitization degree of epoxy resin carbon layer,in brief that the carbon layer is more stable and compact.Through the FT-IR spectrum analysis and XPS analysis of the carbon residue,it can be concluded that there are B-C,P-O,B-O and other chemical bonds in the carbon residue,and the existence of these chemical bonds increases the strength of the carbon layer,and has a certain effect on improving the thermal stability of the carbon layer.Therefore,the flame retardant mechanism of the two flame retardants is the synergistic effect of phosphorus and boron to form a dense carbon layer,which isolates heat and mass transfer,so as to achieve flame retardant effect.