Research On The Properties Of P And N Co-doped Graphene Oxide And Composites

Nowadays,the biggest problem existed in the graphene industry is that there is no complete industrial chain and graphene has not successfully applied in an industrialized product.Due to its high strength,high electrical conductivity and large specific surface area,graphene has the potential to be applied in various fields,including aerospace,lithium-ion batteries,supercapacitors and etc.However,the application of graphene is still in the research stage due to its high production cost.It can be seen from the current research that the most possible industrial application fileld of graphene is to add graphene to the polymer materials,which can greatly enhance the performance of the product such as strength,toughness,electrical conductivity and heat transfer.In this paper,graphene oxide(GO)was firsly functionalized(FGO)by compounds containing phosphorus,nitrogen and phosphorus-nitrogen groups,and then they were added to polymer matrix to produce FGO/flame retardant composite,respectively.The structure and morphology of FGO were characterized,after which the mechanical properties,thermal properties and flame retardancy of the composite were studied.Firstly,graphene oxide(GO)was prepared by Hummer method,and then GO was modified by using hypophosphorous acid,triethylenetetramine and P-N novel compounds,respectively.The structure and properties of P-FGO,N-FGO and PN-FGO were characterized by FTIR,UV,XRD,TG,SEM and TEM.These FGOs with different interlayer spacings were added to epoxy resin.Thermal properties and dispersion property of FGO/EP composite were studied by TGA and SEM,respectively.The flame retardancy and mechanical properties of the composite were investigated by oxygen index,UL-94,tensile and impact tests.The results showed that the thermal stability,the flame retardancy and mechanical properties of the composite were improved compared to the pure epoxy resin.The compatibility and dispersibility of FGO in the composite were improved.In order to explore the effect of the addition of P-FGO on the crystallization behavior of polypropylene,the crystallization behavior,thermal behavior and mechanical properties of the composite were studied.The POM results showed that that when the addition of the P-FGO amount was less than 0.5%,the nucleation of the polypropylene composite increased with the increase of the amount of P-FGO,and the crystallization became more and more complete.It can be seen from the DSC test that the crystallinity and melting temperature increased with the increase in the amount of P-FGO,indicating that FGO can be served as a nucleating agent to promote the crystallization of the polypropylene,which can improve the crystallinity.A new phosphorus-nitrogen flame retardant was synthesized by the reaction of the different phosphorus-containing and nitrogen-containing compounds.The structure was characterized,after which the flame retardant was added to the polyolefin material.It was found that the flame retardant has a good flame retardancy on the polyolefin material.However,since the addition amount was too high,the mechanical strength of the composite decreases.In order to improve the mechanical properties,P-FGO was added to the composite,which can be improved the flame retardancy and mechanical properties of the composite.Whether FGO was added to epoxy resin or polyolefin resin,the mechanical properties of the composite increased firstly and then decreased.This was because that the agglomeration of FGO occured when too much FGO was added,leading to fact that the composite was easily broken with the external force loaded.Therefore,a critical value of the addtion amount of FGO was needed.In addition,compared with adding GO composite,with the same amount of addtion,the increase of flame retardancy,thermal properties and mechanical properties of GO system composite was lower than that of FGO system.Also,the addition of GO and FGO can improve the flame retardant properties of the composite.