Flame Retardancy Of Epoxy Resin Composites Based Two-dimensional Ultra-thin Transition Metal Compounds

Epoxy resin（EP）,as an important polymer materials,has been widely used due to their excellent physical and mechanical characteristics,simple production process and low cost.Although EP has so many advantages,its flammable features greatly limit its application.In this paper,according to the research status at home and abroad,the polymer/two-dimensional ultra-thin compound nano-composites flame retardant system and transition metal flame retardant effect are reviewed.Combining with the research work of this group,it is believed that the combination of nanoscale effects of layered compounds,catalytic carbonization of transition metals,and flame retardancy of phosphorus-containing compounds is expected to become the new flame retardant technology for polymeric materials.Based on this,different types of two-dimensional ultra-thin transition metal compounds nickel cobalt phosphate（NiCoPO₃）and Cobalt hydroxide（Co（OH）₂）were designed and synthesized,and modified by different methods.To further enhance the flame-retardant effect,the lamellar compound cobalt potassium pyrophosphate（CPP）containing Co and P elements was synthesized by solvothermal method.These two-dimensional ultra-thin transition metal compounds were incorporated into EP to study their effect on thermal stability,flame retardancy of EP nanocomposites and investigate their flame retardant mechanism.In this paper,two-dimensional ultra-thin transition metal compound nickel cobalt phosphate（NiCoPO₃）was firstly synthesized by hydrothermal method using cobalt acetate,nickel acetate and sodium pyrophosphate as raw materials,and the surface was modified by graphene oxide（GO）.The chemical structure was determined by XRD,TGA and FTIR tests,which acted as flame retardant and was incorporated into EP.The results confirmed that GO-NiCoPO₃ could promote carbon formation and increase the thermal stability of polymer at high temperature;The combustion tests showed that the LOI values of EP/GO-NiCoPO₃ nanocomposites had been improved,and the UL-94 could pass V-1 level,MCC test results indicated that the THR values of composites could reduce by 41.9%with the addition of 8 wt%GO-NiCoPO₃,and the flame retardant of nanocomposites were improved;which was not only due to the barrier effect of the two-dimensional ultra-thin compound,but also because the transition metal Co,Ni and P elements could promote carbon formation,and GO contained a large amount of C structure,which enriched the carbon layer content during combustion.The carbonaceous carbon structural carbon layer was formed on the surface of the polymer,which improved the stability of the carbon layer,thereby insulating heat and oxygen and inhibiting polymer combustion.In order to further improve the flame retardant performance,this chapter,the two-dimensional ultra-thin transition metal compound cobalt hydroxide Co（OH）₂ was designed and synthesized using cobalt nitrate,sodium chloride and hexamethylenetetramine as raw materials,and the surface was modified by flame retardant sodium polyphosphate(Na₅P₃O₁₀)containing phosphorus,the test results of XRD,SEM,TEM and TGA showed that the pure Co（OH）₂ and Na₅P₃O₁₀-Co（OH）₂were synthesized,which acted as flame retardant and was incorporated into EP.The results of TGA demonstrated that the thermal stability of the polymer was improved at high temperature,and the amount of carbon residues were increased significantly.The UL-94 of the composites could pass V-1 level,the LOI values were increased,and the flame retardancy of nanocomposites was improved.The results of CCT revealed that the effect of smoke suppression was more significant,and the TSP value of the EP/8Na₅P₃O₁₀-Co（OH）₂ nanocomposite was reduced by 51.52%compared to pure EP during combustion;which will be very beneficial for the escape of personnel in a fire.On the one hand,it was due to the barrier effect of two-dimensional ultra-thin compounds,isolating the heat and oxygen exchange between the outside and the polymer substrate;on the other hand,Co（OH）₂ released a large amount of water vapor to dilute flammable gas during combustion.At the same time,Co₃O₄ with catalytic and smoke suppressing effect was formed,which would promote carbon deposition on the surface of the polymer combining with the phosphorus-containing flame retardant Na₅P₃O₁₀.The carbon layer could inhibit further decomposition of the polymer and reduce heat and smoke release,and delay fire.In the chapter,the two-dimensional ultra-thin compound cobalt potassium pyrophosphate（CPP）containing both Co and P elements was designed and synthesized by simple solvothermal method so as to further improve nanocomposites flame retardant properties,simplify the experimental process.The chemical structures were determined by XRD and TGA.The results of SEM and TEM showed that it had a typical ultra-thin layered morphology and was well dispersed in EP matrix by in-situ polymerization.The nanocomposites were carried out a series of tests.The TGA results evidenced that the carbon residue of EP/8 CPP at 700°C was as high as 30.5wt%,indicating that CPP had excellent condensed phase catalytic carbon performance.The combustion cleared that the LOI value of the EP/10 CPP nanocomposite was significantly improved to 35.9%,which was 10.1%higher than the pure EP,and the UL-94 of nanocomposites could reach V-1 with the addition of 6 wt%CPP,the results of CCT maintested that the values of HRR,THR,SPR,and TSP decreased evidently.This may be due to the fact that CPP was thermally decomposed to release a large amount of water vapor to dilute the flammable gas and oxygen concentration in the air,at the same time,PO·free radical was generated,which could combine with the H·and HO·radicals burned in the air to interrupt the chain combustion reaction and exert the flame retarding effect.In addition,CPP had excellent catalytic carbonization capability,which could promote the formation of carbon into the polymer,and the Co oxygen compound and the P-C structure generated during the decomposition were remained in the carbon residue to increase the content of the carbon layer,delaying the diffusion of oxygen and heat,reducing the release of smoke and improving the safety of fire.This will be very meaningful for protecting people’s lives and property safety and reducing environmental pollution.