The Construction Of Organic-Inorganic Nano-Hybrids And Study On The Flame Retardancy Of Synergistic EG In Low Density Polyethylene

Low density polyethylene（LDPE）has the advantages of economy,low toxicity,good electrical insulation,low dielectric loss and good functionality.It has been used in the manufacture of composite materials such as thin films,pipes,diverters,capacitors,battery diaphragms and sensors.However,LDPE is highly flammable material,combustion release a lot of combustion heat,and there are droplet generation,easy to cause"secondary fire",so its fire safety problem has attracted much attention.In the field of LDPE flame retardant research,the intumescent flame retardant（IFR）is the most promising flame retardant,among which the inorganic expansive flame retardant represented by expandable graphite（EG）has a wide range of applications,however,inorganic expansive flame retardant only when a large number of added will have a certain flame-retardant effect,which will seriously damage the processing properties of composite materials,mechanical properties.Therefore,taking EG as the main flame retardant,it is of great significance to explore how to improve its fire-retardant efficiency.In the paper,Phytate-melamine-MnO₂ nano-hybrids（PM-MnO₂）were prepared by one-pot method.And then,LDPE composites of PM-MnO₂ and EG with different mass ratios were prepared by melting blending method.Thermogravimetric analysis（TGA）and cone calorimetric test（CC）were used to characterize the thermal degradation behavior and flame retardancy of LDPE composites.The main research contents and results are as follows:Firstly,using phytic acid（PA）,melamine（MA）,potassium permanganate（KMnO₄）,ethyl acetate（EA）and distilled water as raw materials,the one-pot method is used in the two-phase solution system to realize the layer-by-layer self-assembly of MnO₂,MA and PA by using the way that the two-phase solution gradually transforms into single-phase solution when EA is hydrolyzed by heat.Construct PM-MnO₂ nano-hybrids.The preparation conditions of PM-MnO₂ were investigated by single factor experiment.By X-ray diffraction（XRD）,scanning electron microscopy（SEM）,etc.The optimal morphology concentration of PM-MnO₂ was determined as n（MA）:n（PA）:n（KMnO₄）=8:1:8（PM8-MnO2-8）.n（MA）:n（PA）:n（KMnO₄）=6:1:4（PM6-MnO₂-4）followed.The results showed that part of the cations of melamine bonded with the MnO₂ nanosheet by electrostatic action,and then the rest of the amines crosslinked with phytic acid through neutralization reaction,and gradually formed the hybrid.In addition,the thermal stability of PM6-MnO₂-4 was characterized by TGA and XRD.The results show that the carbon residue of PM6-MnO₂-4 is 40.2%at 800℃,and the thermal degradation behavior of PM6-MnO₂-4 is analyzed.Secondly,the problem that EG is easy to produce"fly ash"when it is heated and expanded rapidly in the LDPE matrix is studied.Firstly,PM8-MnO₂-8 and PM6-MnO₂-4 synergistic LDPE composites with EG were prepared by fusion blending method according to the experimental formula.Then,the fire-retardant formula of LDPE was optimized by vertical combustion（UL-94）and limiting oxygen index（LOI）test.The results showed that the synergistic flame-retardant effect of PM6-MnO₂-4 and EG was better than that of PM8-MnO₂-8 and EG when the total flame-retardant content was 30 wt%.Among them,LDPE/PM6-MnO₂-4/EG fails to pass the UL-94 test and the LOI value is only 25.5%,but LDPE/PM6-MnO₂-4/EG passes the UL-94 test and the LOI value increases to 26.9%,indicating that m_{（PM6-MnO2-4）}:m_（EG）=1:5 is the optimal mass ratio.Finally,the synergistic fire safety performance of PM6-MnO₂-4 and EG was studied by CC test.Compared with LDPE0,the peak heat release rate（p HRR）,peak CO₂ production rate（CO₂P）and peak CO production rate（COP）decrease by 81.8%,77.3%and 72.0%,respectively.It was proved that the residual carbon density increased,"fly ash"weakened,PM6-MnO₂-4 and EG synergistic flame retardant.Thirdly,in order to further explore the synergistic flame-retardant mechanism of PM6-MnO₂-4 and EG.Firstly,the thermal degradation behavior of LDPE composite was analyzed by TGA test.The results show that the residual carbon content of LDPE/PM6-MnO₂-4/EG increases to20.9%at 800℃,which has the best thermal stability at high temperature.Then,the morphology,graphitization degree and chemical composition of carbon residues tested by CC were analyzed by scanning electron microscopy（SEM）,Raman analyzer,X-ray photoelectron spectroscopy（XPS）,etc.The results showed that the combination of 5 wt%PM6-MnO₂-4 and25 wt%EG could significantly improve the graphitization degree of carbon residues of LDPE composites.PM6-MnO₂-4 catalyzes cross-linking into carbon,which improves the continuity and densification of carbon layer,and improves the physical barrier effect of carbonized layer,which proves that there is a significant synergistic effect between PM6-MnO₂-4 and EG.