Study On The Flame Retardant Properties Of Hydromagnesite And Synergistic Agent In EVA

Hydromagnesite(Mg₅(CO₃)₄(OH)₂·4H₂O,HM for short)is a widely distributed natural basic magnesium carbonate mineral.As a new type of environmental friendly natural mineral flame retardant,hydromagnesite has great cost advantages.Natural hydromagnesite can be a substitute of aluminum hydroxide and magnesium hydroxide and be used as a new mineral type flame-retardant filler.Ethylene-vinyl acetate copolymer(EVA)is one of the most widely used polymer materials.However,it is too much flammable with a much lower limiting oxygen index(LOI)value of only 17%to 19%,cause serious fire hazard.These shortcomings may severely restrict the application of EVA in related fields.Therefore,it is very necessary to reduce the fire hazard of EVA itself.Focusing on the above problems,this study first applied HM with particle sizes of D50=4.04?m and 12.38?m to prepare flame-retardant composites HM¹/EVA and HM²/EVA respectively,and compared their flame retardancy with the brucite(MDH)composites MDH/EVA,confirming the feasibility of HM as a flame-retardant filler for polymer composites.The composite HM¹/EVA containing the smaller particle size HM had better flame retardancy and mechanical properties than composite HM²/EVA.Secondly,by adding three different synergists,silicone(SIC),rod-shaped zinc borate(ZB)and sepiolite(SEP)separately with HM into composites,the effect of the synergist type,the synergist addition amount,the total amount of synergist and HM on the flame retardant and mechanical properties of composite materials were investigated.Finally,O174 silane coupling agent was used to dry-modify HM,and then SEP and modified HM were compounded to prepare composite materials.The effect of HM on the flame retardant and mechanical properties of composites before and after the modification was compared and studied.The main research contents and conclusions of this study are as follows:(1)HM,as a flame-retardant filler,had similar properties to brucite MDH,and can improve the LOI value,performance in vertical burning test and carbonization properties of composite HM/EVA.When the addition amount of HM was increased to 60 wt.%,the particle size of HM had almost no effect on the vertical burningburning test.Compared with the composites HM²/EVA,the composites HM¹/EVA prepared with a particle size of D50=4.04?m had better overall performance in TTI,THR and TSP,and the residual carbon was denser.The mechanical properties of the EVA composite material was slightly improved.(2)The effect of SIC,ZB and SEP used as synergists on properties of compositeswere investigated systemically.(1)When the addition amount of ZB or SEP was 9 wt.%,the total addition amount(wt.%)of ZB and HM in the composite material was 40,50 and 60 respectively.When the total addition amount of SEP and HM(wt.%)was 50 and 60 respectively,the LOI of composite materials ZB-HM/EVA and SEP-HM/EVA could reach 30%,which could meet the general requirements for flame retardant materials.(2)When the total addition amount of HM and ZB was 40 wt.%,the synergistic effect of ZB and HM on the vertical burningburning of composite materials was more significant.When the total addition amount was greater than or equal to 50 wt.%,the composites contaning the two synergists SIC and SEP tended to perform better in the vertical burning test,and there was no dripping during the combustion process with the UL-94 level to be V-0,Paricularly,when the total amount of HM and synergist was 60 wt.%,and the amount of synergist SEP(wt.%)was 3,6 and 9 respectively,the burning time(t₁+t₂)of the composite material was less than 1.0 s,showing excellent vertical burning performance.(3)When SIC was used as a synergist it has a negative impact on the smoke suppression performance of composite SIC-HM/EVA.The rod-shaped ZB and SEP could improve the thermal shielding performance and smoke suppression performance of the composite material,and the composite material SEP9-HM51/EVA showed good smoke suppression and thermal shielding performance at the same time.However,the change of the addition amount of ZB and SEP did not affect significantly the smoke suppression performance of the composites.(4)Compared with the composite material of SIC and ZB,the performance in carbonization of the residual carbon was better when 9 wt.%of SEP was added,and a silicon-carbon protective layer was formed on the surface.When the total addition amount increased to 60 wt.%,there were a relatively flat and dense carbon layer formed on the residue surface of composite materials SIC-HM/EVA,ZB-HM/EVA and SEP-HM/EVA,and the surface of the carbon residue was white and gray.The residual mass was greater.In particular,the composite material SEP9-HM51/EVA prepared with 9 wt.%SEP addition had basically no cracks on the outer surface of the carbon residue,and the carbon residue structure was denser,Its integritywas relatively better maintained,and a dense Mg O protective layer was formed on the surface of the carbon residual.(3)With the increasing of total added amount of three synergists and HM the tensile strength and elongation at break of composite materials HM/EVA,SIC-HM/EVA,ZB-HM/EVA and SEP-HM/EVA decreased too much comaring to those of pure EVA.However,comparing the three composparallelly,when the total addition amount of HM and SEP was 60 wt.%,the mechanical properties of SEP-HM/EVA composites performed the best.When the total amount of synergist and HM for the three composites was the same,the decrease of the composites`tensile strength followed the sequence:(SEP+HM)>(ZB+HM)>(SIC+HM),and the decrease of elongation at break followed:(SEP+HM)>(SIC+HM)>(ZB+HM),indicating that the synergistic combination of SEP and HM had a smaller impact on mechanical property of the composites SEP-HM/EVA.Comparing with the synergistic combination containing ZB and HM,the synergistic combination containing ZB and HM performed better in terms of tensile strength,but worse in the elongation at break.The decreasing effet of the synergist on the composite tensile strength and elongation at break follows in descending order:HM>SEP>ZB?SIC.It showed that the increase of HM addition was the most critical influencing factor for the decrease of tensile strength and elongation at break of the composite materials.(4)Dry modification of HM powder with O174 silane coupling agent was conducted,and the optimal conditions for dry modification of HM powder was as follows:the modification time was 10 min,modification temperature was 140?,the amount of O174 silane was 1.5 wt.%.Compared with the composite material SEP9-HM51/EVA,the LOI value of the composite material m SEP9-HM51/EVA with O174 silane coupling agent modification reached 34.2%,and the improvement rates was 2.9%.The UL-94 level was maintained at the V-0 level and there was no dripping phenomenon at the same time.THR was reduced by 19.72%,and TSP was reduced by 7.14%.The tensile strength increased by 21.32%,and the elongation at break increased 27.45%.All these demonstrated that HM modified with O174 silane coupling agent could effectively improve the flame retardancy,smoke suppression and mechanical properties of the composite m SEP9-HM51/EVA.