Effect Of Modified LDHs And APP/CFA Composite Flame Retardants On The Flame Retardancy Of EVA

In recent years,layered double hydroxides(LDHs)had been widely used in halogen-free flame retardants because of their special layered structure and good thermal stability.However,when LDHs were used as flame retardants individually,it was generally necessary to add a large amount of LDHs to achieve the desired flame retardant effect.However,adding a large amount of flame retardants will reduce the mechanical properties of material.Therefore,in this thesis,the composite flame retardants containing LDHs,ammonium polyphosphate(APP)and charring-foaming agent(CFA)were prepared and used to improve the flame retardancy of Ethylene-vinyl acetate copolymer(EVA).And the thermal stability,flame retardancy,smoke suppression and mechanical properties of the composites were characterized and analyzed.In this paper,microwave hydrothermal crystallization co-precipitation method was used to synthesize modified MgAl-LDHs.X-ray diffraction(XRD)and Fourier infrared spectroscopy(FT-IR)jointly proved that interlayer anion of the synthetic stearate sodium surface modified LDHs was Co32-.Composites containing LDHs,APP,CFA and EVA were prepared by melt-blending method.The maximum temperature of polyethylene chain scission for all composites was 38? higher than that of pure EVA.When 4 g MgAl-LDHs were added,the peak value of heat release rate(pk-HRR)of composite ELDH4 containing LDHs,APP,CFA and EVA was reduced by 80%compared with pure EVA,with the highest LOI value(30.3%)and passed the vertical combustion test(UL-94)to reach the V-0 level.Scanning electron microscopy(SEM)and digital photos of residues indicated that the synergistic effect of modified MgAl-LDHs,APP and CFA can promote the formation of dense and stable carbon layers.Therefore it had an effective flame retardant effect on the EVA matrix.The composite can still maintain good tensile strength,and ELDH12 has the highest toughness due to the synergistic effect between the modified MgAl-LDHs,APP and CFA.The melamine,pentaerythritol and sodium hypophosphite with flame retardant effect were intercalated to synthetic surface-modified ZnMgAl-LDHs by microwave hydrothermal crystallization co-precipitation method.XRD results showed that the intercalated ZnMg-Al LDHs was prepared successfully.Intercalation of melamine,pentaerythritol and sodium hypophosphite improved the hydrophobicity of LDHs.The combination of LDHs with APP and CFA was applied to the investigation of flame retardant EVA.The pk-HRR of composites containing LDHs,APP,CFA and EVA were all reduced by more than 68%compared to pure EVA.The LOI values were all increased by more than 68%compared to pure EVA.Meanwhile,composites had passed UL-94 test and reached the V-2 level.The synergy between the modified ZnMgAl-LDHs,APP and CFA was beneficial to promote the formation of a stable carbon layer during the combustion process.Sodium stearate surface-modified MgAl-LDHs containing trace rare earth elements(La,Ce and Nd)were prepared by microwave hydrothermal crystallization co-precipitation method and combined obtained LDHs with APP,CFA and EVA to form the flame-retardant composites.The maximum thermal degradation temperature of composite is 37? higher than that of pure EVA.The synergy between APP,CFA and MgAl-LDHs containing REEs enabled the composites to successfully pass the UL-94 test and reach V-0 level.The values of pk-HRR for composites containing modified MgAl-LDHs,APP and CFA with REEs decreased by more than 82%compared with pure EVA.The composites containing APP,CFA and LDHs with REEs exhibited lower pk-HRR,pk-SPR,and pk-COP in comparison with composites without REEs.The results showed that the addition of trace REEs had greatly improved the flame retardancy and smoke suppression of EVA.