Study On Flame Retardant Modified Epoxy Resin With Multi-Element Graphene Hybrid System

With the continuous development of society,epoxy resin has been widely used in social production and life,but its flammability is still a major drawback.In response to the call for"sustainable development",it is also to meet the needs of human survival,the development of new low-toxic and high-efficiency flame retardants is in full swing.Graphene has attracted extensive attention of researchers due to its non-toxicity,excellent mechanical properties and flame retardant properties,and also has opened up new design ideas.However,the application of graphene in epoxy matrix must overcome the problem of poor compatibility.The appearance of graphene oxide(GO),which is the precursor of graphene and containing a large number of reactive groups,provides a feasible path for the good application of functionalized graphene in polymer matrix.Phosphorus,nitrogen and silicon-containing compounds are often used in the development of flame retardants for polymer matrix materials due to their superior flame retardancy and low toxicity.Therefore,a compound containing flame retardant elements such as phosphorus,nitrogen and silicon is skillfully grafted onto the surface of GO,and it is expected to obtain a green and highly effective flame retardant.In this paper,graphene oxide was used as a carrier,which was respectively modified by the small molecule and polymer contained flame retardant elements such as phosphorus,nitrogen and silicon to obtain graphene-based flame retardants.And they were added to epoxy resins in different ratios.Furthermore,the effects of functionalized graphene obtained through different modification methods on the flame retardancy,thermal stability and mechanical properties of the composites were discussed.The main research contents were as follows:1.Using the classical Kabachnik-Fields reaction,APTES,DOPO and poly-oxymethylene were used as raw materials to synthesize APTES-bisDOPO quickly and easily.Then the hydrolysis reaction was used to obtain functionalized graphene oxide(FGO).The FGO was introduced into an epoxy system and cured by a process to obtain the flame retardant epoxy resin.It was proved that the characteristic peak of the gaseous decomposition product from phosphorus-containing compound appeared before the highest degradation temperature(381?).After 381?,the characteristic peaks of aliphatic and CO2 were gradually obvious,which meant that the APTES-bisDOPO structure of FGO preferentially decomposed and released gas,while the higher thermal stability of FGO helped to retard thermal degradation of aliphatic and CO2-related groups.At the same time,FGO could improve the flame retardancy of the composite by increasing the residual carbon and promoting the formation of a stable carbon layer,preventing the infiltration of heat and volatile products,and further slowing the release rate of heat.However,when the amount of FGO added reached 3 wt%,the interaction in FGO which was similar to that of the graphene sheets,resulting that there were certain aggregations in the epoxy matrix,which affected the mechanical properties of the composites.2.MPS-GO was obtained through hydrolysis reaction between graphene oxide and the silane coupling agent MPS(KH-570)with double bonded.Then graphene oxide modified with polymer(HM-GO)was obtained by the polymerization of MPS-GO and HEPO containing double bonds.HM-GO was successfully synthesized by XPS,XRD,Raman and other test methods.Then HM-GO was as a flame retardant of epoxy resin,EP composites with different additions were obtained.In this system,the flame retardancy of the composites increased with the increase of HM-GO contents.When the addition amount reached 4 wt%,the LOI value could reach 31.0%,which increased by 28.6%,compared with EP-0(24.1%).The PHRR value also decreased from 515.8 W g-1 of pure epoxy resin to 376.9 W g-1.The results of Raman and SEM analysis showed that when the addition of HM-GO was a little,the gas phase flame retardant produced by the phosphorus-containing groups played a dominant role.When the addition of HM-GO was increased,the graphene structure helped to form a more orderly and stable carbon layer,which was like a barrier to protect the matrix from heat and oxygen erosion.The carbon layer was mainly composed of aromatic structure and Si-O-Si.In addition,with the increase of HM-GO content,the Tg value,flexural strength and flexural modulus of EP composites were increased.When the content of HM-GO was 4 wt%,the maximum flexural strength reached 119.39 MPa,which increased by 39.44%.The flexural modulus also increased from 216.88 MPa of pure epoxy resin to 2539.87 MPa.It was also proved by calculation that the increase of Tg was due to the increase of crosslinking density.The steady improvement of flame retardancy and mechanical properties of composites indicated that these flame retardants had better compatibility with epoxy matrix.