Synthesis And Characterization Of Two-component Acidic Ion Intercalated Layered Double Hydroxide And Its Use As A Flame-retardant In Ethylene Vinyl Acetate Copolymer(EVA)

Layered double hydroxides(LDHs)had been recognized as a kind of anionic clay mineral with unique layered structure,interlayer intercalation and anion exchangeability.LDHs can prevent the heat,smoke and oxygen from transferring between underlying materials and flame zone during combustion,and can diluting combustible gas.Thus,LDHs is widely used as flame retardant,heat stabilizer and so on.Two-component acidic ion intercalated LDHs,modified LDHs and exfoliated LDHs were prepared in this study.The structure,thermal stability,mechanical property,rheological property,and non-isothermal crystallization of the prepared LDHs were characterized,respectively.These LDHs were also used as novel nano-flame-retardants in ethylene vinyl acetate(EVA).(1)A series of two-component acidic ion intercalated LDHs(Mg Al Zn-X₁/X₂-LDHs) were prepared by coprecipitation during microwave crystallizing.The resulting material was used as nano-flame-retardant and incorporated into EVA matrix to form nanocomposites,Mg Al Zn-X₁/X₂-LDHs/EVA.The characterization results revealed that the nanocomposites can significantly improve the thermal stability and the thermal oxidative resistance of pristine EVA.The limit oxygen index(LOI)values of Mg Al Zn-X₁/X₂-LDHs/EVA increased by 6%?10%in comparison with pristine EVA(LOI=19).Meanwhile,underwriterslaboratoriestest(UL-94)of Mg Al Zn-X₁/X₂-LDHs/EVA reached UL-94 V-0 rating.The cone calorimeter tests also revealed that the incorporation of Mg Al Zn-X₁/X₂-LDHs into EVA can greatly reduce the smoke formation and heat release in the nanocomposites.(2)The MgAlZn-SnO₃^2-/CO₃^2--LDHs were modified by four surface-modification agents.The modified LDHs were used as nano-flame-retardant and incorporated into EVA with a weight ratio of 40/60.It was found that the modified LDHs can improve the compatibility of LDHs and EVA matrix effectively.They can also improve the flame retardant and mechanical property of Mg Al Zn-Sn O₃^2-/CO₃^2--LDHs/EVA nanocomposites obviously.(3)The exfoliated LDHs were prepared in sodium dodecyl sulfonate formamide solution under microwave crystallization.The resulting solution was clear and transparent which indicated that the hydrotalcite was exfoliated successfully.The characterization results of mechanical property,rheological property and SEM,also revealed that exfoliated hydrotalcite was excessively intercalated into the EVA matrix.Thus,the compatibility between LDHs and EVA matrix was improved significantly.The mechanical and rheological properties of the exfoliated LDHs were also improved.(4)The non-isothermal crystallization behaviour of the intercalated LDHs,modified LDHs,and exfoliated LDHs in EVA nanocomposites were studied by DSC.The results show that the initial crystallization temperature(T₀),the crystallization peak temperature(T_p),and the end crystallization temperature(T_e)of these nanocomposites were all shifted to a lower temperature region with the increase of cooling rate?.Crystallization rate:exfoliated LDHs/EVA>modified LDHs/EVA>intercalated LDHs/EVA>EVA pristine matrix.This tendency shows that the dispersion degree of different hydrotalcite in EVA matrix can promote the crystallization rate of the resulting nanocomposites.The higher dispersion degree and crystallization rate can give rise to better mechanical properties of the LDHs/EVA nanocomposites.