In-Situ Synthesis Of Several Typical Hydrotalcite Hybrid Materials And Its Flame Retardancy In EVA Composites

Hydrotalcite?also known as layered double hydroxide,LDH?,as a kind of environmental friendly flame retardant,has many problems such as large dosage and low efficiency,so its application is limited.In this work,three kinds of hydrotalcite hybrid materials of LDH-Si,LDH-Ti and LDH-Si/Ti were in-situ synthesis using silica?SiO₂?and titania?TiO₂?as synergistic agents.The products were characterized using X-ray diffraction?XRD?and EDS.Subsequently,EVA/LDH-Si composites,EVA/LDH-Ti composites and EVA/LDH-Si/Ti composites were prepared by melt blending method.Flame retardant,smoke suppression and thermal degradation properties of the composites were characterized via cone calorimetry test?CCT?,limiting oxygen index?LOI?,scanning electronic microscopy?SEM?,smoke density test?SDT?,thermogravimetry-Fourier transform infrared spectrometry?TG-IR?and so on,and the mechanism of flame retardant and smoke suppression was explored.Results showed that flame retardant,smoke suppression and thermal degradation properties of EVA/LDH-Si composites,EVA/LDH-Ti composites and EVA/LDH-Si/Ti composites were clearly improved compared with pure EVA and EVA/LDH composites?ELDH?.?1?The results of XRD and EDS confirmed that three kinds of hydrotalcite hybrid materials of LDH-Si,LDH-Ti and LDH-Si/Ti can be prepared successfully by in-situ synthesis method,and they have well-formed crystalline layered structure.?2?The heat release rate?HRR?,total heat release?THR?,mass loss and smoke production rate?SPR?of the EVA/LDH-Si composites declined significantly compared with EVA and ELDH.The peak heat release rate?pHRR?of the EVA/LDH-Si composites was only 195 kW/m² after the addition of 47.5%LDH-2.5%Si to EVA,which was respectively reduced by 87.1%and 28.5%,compared with EVA and ELDH.And the luminous flux of the composites was kept above 88.2%with the application of the pilot flame.Moreover,the LOI value of the EVA/LDH-Si composites can be as high as 30.8%.Compared to ELDH,EVA/LDH-Si composites show a higher thermal stability with carbon yield of up to 32%.?3?The HRR,THR,mass loss and SPR of the EVA/LDH-Ti composites significantly reduced than pure EVA and ELDH.When the addition of 49%LDH-l%Ti,The pHRR of the EVA/LDH-Ti composites was only 207.2 kW/m²,which was respectively declined by 86.3%and 24.1%than pure EVA and ELDH.And its LOI value can be as high as 29.8%.When a pilot flame was applied in the test,the luminous flux of the EVA/47.5%LDH-2.5%Ti composites was kept above 75%.Moreover,the EVA/LDH-Ti composites show a higher thermal stability than ELDH.?4?Compared to pure EVA and ELDH,the HRR,THR,mass loss and SPR of the E VA/LDH-S i/T i composites significantly reduced.When the addition of 47.5%LDH-1.5%Si/l%Ti,the pHRR of the EVA/LDH-Ti composites was only 164.7 kW/m²,which was respectively declined by 89.1%and 39.6%than pure EVA and ELDH.And its LOI value can be as high as 30.7%.Moreover,the luminous flux of the EVA composites was kept above 90%with the application of the pilot flame.Besides,the EVA/LDH-Si/Ti composites show a higher thermal stability with carbon yield of up to 34.7%.?5?The hydrotalcite hybrid materials can obviously improve the flame retardant efficiency using the SiO₂ and TiO₂ as synergistic agents of LDH.Its synergistic mechanism is mainly the condensed phase flame retardant.SiO₂ and TiO₂ can form a protective carbon layer with the metal oxides formed by the decomposition of LDH,and improve its morphology,resulting in the improvement of the flame retardant,smoke suppression and thermal degradation properties of the materials.