Preparation,Modification And The Flame Retardant Application Of Graphite Oxide And Graphene

Graphite oxide?GO?is an important graphite derivative and a precursor for the macro quantities preparation of graphene.Because it can reduce the heat release of materials,isolate the transport of combustion gases and increase the amount of carbon residue,the use of GO as a flame retardant additive is receiving attention.However,the existence of vander-Waals force and the?-?attraction between the graphite sheets results in the inhomogeneous distribution of GO in the polymer matrix,which leads to poor flame retardancy.In this study,a pressurized oxidation and an ammonia-hydrazine-based multiplex reduction were provided to prepare GO and grapheme with large size of 10²0?m through two temperature control stages.The natural graphite with a size of 50 mesh,80 mesh,100 mesh and 150 mesh were used as raw materials,respectively.The structure,morphology,elemental composition,functional group,thermal stability and thickness of these products were characterized.And then,in order to improve the dispersibility,the GO prepared by 150 mesh raw material graphite was further modified.GO modified with zinc ferrite was prepared.Finally,the modified GO was used for the flame retardancy of epoxy resin?EP?and polylactic acid?PLA?,respectively.The synergistic flame retardant effect between modified GO and ammonium polyphosphate?APP?was investigated.The research contents discusse as follows:First,with 50 mesh,80 mesh,100 mesh and 150 mesh natural graphite as materials,GO₅₀,GO₈₀,GO₁₀₀,GO₁₅₀ and its reduction products of graphene were prepared by using pressurized oxidation and an ammonia-hydrazine-based multiplex reduction method,respectively.Compared with the modified Hummers method,the used closed oxidation method requires only two temperature control stages,and the conditions are easy to control.The yield of GO prepared from 150 mesh raw graphite can reach 14.7%.The characterization of X-ray diffraction?XRD?,scanning electron microscopy?SEM?,atomic force microscopy?AFM?,Raman spectroscopy?Raman?and Fourier transform infrared spectroscopy?FTIR?confirms that 50 mesh,80 mesh,100 mesh and 150 mesh graphite can be used to prepared GO and grapheme with a size of 10²0?m.The experimental results show that with the decrease of graphite particle size,the yield of GO,the degree of sheet peeling and thermal stability are improved.The prepared graphene shows a thickness of about 1.0 nm,and it indicates good thermal stability at 800°C with the residue yield in the range of 80%⁸5%.Second,in order to improve the dispersibility and surface structure of GO,the GO,prepared with 150 mesh natural graphite was modified with zinc chloride and ferric chloride.GO modified by zinc ferrite?ZnFe₂O₄,marked as ZF?was prepared,and labeled as MZF-GO.SEM,energy scattering spectroscopy?EDS?,XRD,FTIR and TG/DTG analysis were performed on ZF and MZF-GO.The results show that compared with GO,the dispersibility of MZF-GO is obviously enhanced,and the thermal stability is improved.The residue yield at800°C can reach 87.3%.Third,for the purpose of flame retardant of EP,the influences of MZF-GO,APP,and the mixtures of MZF-GO and APP in different proportions on the combustion performance,thermal stability and mechanical properties of EP were studied.The experimental results show that:?1?MZF-GO plays a role in solid phase to prevent melting and dripping.While,the APP exhibits flame retardance in the gas phase.The limiting oxygen index and vertical burning level of the 94EP/1MZF-GO/5APP composite reach the requirements of flame retardant material.?2?The heat release rate,peak value heat release rate,total heat of release,smoke generation rate and total smoke generation of the flame retardant PE composites show obvious decrease.?3?The addition of the mentioned flame retardants reduce the tensile strength and impact strength of EP.Finally,the flame retardant effect of MZF-GO,APP and the mixtures of MZF-GO and APP on PLA was further investigated.The results show that:?1?When MZF-GO and APP are added in a mass ratio of 1:1,94PLA/3MZF-GO/3APP shows the best flame retardancy.?2?The addition of MZF-GO reduces the low temperature thermal stability of PLA and improves its high temperature thermal stability.The introduction of APP can simultaneously increase the low temperature thermal stability and high temperature thermal stability of PLA.?3?The investigation for material mechanical properties indicates that addition of flame retardant reduces the tensile strength,but its tensile elongation is improved.