Preparation Of Mesoporous Zinc Ferrite-graphene Oxide?Zinc Ferrite Nanorods Flame Retardants And Their Effect On The Flame Retardancy Of Expoy Resin

Epoxy resin(EP)is widely used in many fields,such as space,transportation and electronics due to its excellent mechanical and chemical properties as well as easy processing.However,the inherent flammability of EP significantly restricts its application in many areas.In recent years,zinc hydroxystannate(ZHS)as the representative halogen-free flame retardants has aroused researchers' concerns in order to reduce the harms to human body and environment caused by halogen flame retardants.Particularly,in our previous studies,a series of ZHS nanohybrids flame retardants have been prepared and show that they can effectively improve the flame retardance of poly(vinyl chloride)and EP.But the rare reserve of tin element in the earth's crust is unfavorable for its wide application.For addressing these issues,in this paper,we chose the abundant and low-cost iron instead of tin to prepare mesoporous zinc ferrate and zinc ferrate nanorods instead of zinc stannate nanoparticles via controlling the reaction condition.The main studies include two topics.On the one hand,we utilize MZF to modify graphene oxide(GO)to fabricate mesoporous zinc ferrite-graphene oxide(MZF-GO)nanohybrids flame retardants through a one-step hydrothermal method.In this way,the confinement effect of the mesoporous of MZF can improve the thermal stability and inhibit the droplets dripping of EP;and the mesoporous structure of MZF can absorb flammable gases,thus improving the flame retardancy of EP;meanwhile,the unique two-dimensional layered structure and the large specific surface area of GO can promote the formation of dense and continuous carbon layer of the polymer,which can block the heat and gas transmission and improve the flame-retardant properties.On the other hand,we also fabricate one-dimensional zinc ferrite nanorods(R-ZFO)flame retardants because one-dimensional materials can form network structure in the EP,which can enhance the strength of the carbon layer;at the same time,one-dimensional material has unique advantages in enhancing the mechanical properties of polymer.The structure and morphology of MZF-GO and R-ZFO were characterized by X-ray diffract(XRD),Fourier transform infrared spectrometry(FTIR),Brunner-Emmet-Teller(BET)measurements,Transmission electron microscopy(TEM)and so on.The flame retardancy and mechanical properties of EP filled with MZF-GO and R-ZFO were evaluated by limited oxygen index(LOI),cone calorimetry,tensile strength and so on.Finally,the flame-retardant mechanism was determined by SEM,Raman and XRD analysis of the morphology and structure of the carbon layers after combustion.These main results and contents were as follows: 1.Preparation of MZF-GO nanohybrids flame retardants and their effect on the flame retardancy of EPThe MZF-GO nanohybrids were successfully prepared by modifying MZF on the surface of GO via a hydrothermal method.The pictures of SEM and TEM show that MZF nanoparticles were homogeneously distributed on the GO layer and inhibited the restack of GO.And the diameter of the MZF is around 20 nm.The results of BET indicate that the pore size of MZF is about 3.9 nm.Subsequently,3 wt.% of MZF-GO,GO and ZHS-GO were added into EP to evaluate flame retardancy,respectively.The results show that GO,ZHS-GO and MZF-GO increased the LOI of EP from 22.0 to 22.2,24.2 and 27.2,respectively.The cone results show that compared with pure EP,the peak heat release rate(pHRR),total heat release and total smoke release rate(TSR)of MZF-GO/EP decreased by 39.57%,22.69% and 32.56% respectively.MZF-GO/EP achieved the best flame retardancy in all samples.The residues of EP nanocomposites were characterized by SEM,Raman and XRD and the result show that MZF-GO obviously leads to the increase of char yield and the formation of a continuous and compact char layer,which can inhibit the degradation products,heat,and oxygen transfer to protect the underlying EP matrix as an effect barrier.In addition,the mesoporous structure of the MZF can absorb some flammable gases and volatiles during the process of decomposition and prevent the dripping of the droplets.2.Preparation of R-ZFO flame retardants and their effect on the flame retardancy and mechanical properties of EPR-ZFO and zinc ferrite nanoparticles(NP-ZFO)were synthesized by microesolution method and co-precipitation method respectively.The structure and morphology characterization from TEM and SEM show that the diameter of R-ZFO is about 200 nm,and the length of R-ZFO is in the range of 1 ?m~10 ?m,while the diameter of NP-ZFO is about 10 nm.The effect of R-ZFO and NP-ZFO on the flame retardancy and mechanical properties of EP were studied at the loading of 3 wt.%.Compared with other samples,R-ZFO showed the best flame retardancy.R-ZFO significantly reduced the pHRR,the carbon monoxide release rate(COPR)and TSR by 34.16%,23.21% and 5.36% respectively.At the same time,the time to pHRR was prolonged from 135 s to 195 s.R-ZFO can improve the residual carbon content of EP from 0.24% to 10.27%.And the results from LOI show that R-ZFO can improve the LOI from 22.5 to 28.3.The reason why R-ZFO can significantly improve the flame retardancy of EP is that the network structure that formed by R-ZFO in the EP,which can act as barrier to slow down the combustion process.In addition,The SEM and Raman characterization of char show that R-ZFO can promote the formation of high-quality graphitization carbon layer in the combustion,which can act as better protective effect.Thereby R-ZFO can effectively enhance the flame retardant properties of EP.Meanwhile,it can be found that R-ZFO/EP has a better mechanical property than NP-ZFO/EP does.The storage modulus of EP can be improved because the network structure formed by R-ZFO can limit the spread of EP molecular chain.