| Layered double hydroxides (LDHs) have drawn enormous attention as environmental fire retardant in recent years for they have shown good flame retardancy and smoke suppression due to their unique chemical composition and layered structure. The investigations on the flame retardancy of LDHs focus on three aspects:the effects of different metal cations on flame retardancy; the effects of different anions on flame retardancy; the synergistic effect between LDHs and other fire retardant. A novel hydroxide was prepared and introduced into ethylene vinyl acetate (EVA) composite and EVA containing an intumescent flame retardant (IFR) system in order to improve the thermal stability and flame retardancy. This paper contains the following two part research work:1. NH2SO3-1 was intercalated into layered double hydroxide to prepare a novel sulfamic acid-intercalated MgAl-LDH (SA-LDH) through acid-base reaction. Fourier transform infrared (FT-IR) analysis confirmed the presence of sulfamic acid in LDH. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were also used to characterize the structural morphology of SA-LDH, and the results revealed that the interlayer space of LDH had been enlarged from 0.76 to 0.91 nm and proved the formation of hydrogen bond between SA-LDH. FT-IR, XPS, XRD and UV spectrophotometer were used to characterize the EVA/SA-LDH composite and the result revealed that SA-LDH has good compatibility with EVA. The flammability properties and thermal stability of EVA and its composites were evaluated using thermogravimetric analysis (TGA), cone calorimeter, limiting oxygen index (LOI), and the UL-94 protocol. The LOI can achieve 24.7% at loading fraction of 20% LDH. While compared to EVA/LDH composite, PHRR, and PHRR2 values for EVA4 are reduced by 28.2% and 34.5% from a value of 883.3 to 633.8kW/m2 and 934.5 to 612.4kW/m2 as well as the AMLR from 18.7 to 12.3g/sm2. Synergistic effects were observed in cone calorimetry for the formulation containing MgAl-NH2SO3-LDH. SA-LDH shows better fire resistance than LDH.2. NH2SO3-1 intercalated MgAl-LDH (SA-LDH) was prepared and introduced into ethylene vinyl acetate (EVA) composite containing an intumescent flame retardant (IFR) system in order to improve the thermal stability and flame retardancy of EVA. The structure and thermal stability of SA-LDH is characterized by the FTIR, XRD, TEM and TG analysis. The flame retardancy and smoke suppression was evaluated by limiting oxygen index (LOI), vertical burning UL-94, and cone calorimeter (CONE) tests. The LOI increased to 26.9% at the presence of 1 phr SA-LDH. The twin peaks were observed for EVA composites containing IFR, and the PHRR, and PHRR2 of EVA/19 phr IFR/1 phr SA-LDH sample are 504 and 584.5 kW/m2 respectively which are reduced by 15.7% and 30.2% compared with that of the EVA/20 phr IFR sample. The morphology of char after combustion was characterized by scanning electron microscope (SEM), and it revealed more compact char structure was formed at the presence of SA-LDH.3. Phosphaphenanthrene based carboxylic acid (DM) was synthesized by reacting 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) with maleic acid (MA). DM anion was then intercalated into layered double hydroxide (LDH) before being introduced into ethylene vinyl acetate (EVA) copolymer in order to improve the fire performance of the composite. XRD results revealed that the interlayer space of LDH was enlarged from 0.77 to 2.12 nm by DM intercalation. Key characteristic bands of DM anionic were observed in the FT-IR spectrum of DM-LDH. The flame retardancy of EVA composites was evaluated by limiting oxygen index (LOI), UL-94 and the cone tests, and the results demonstrated the introduction of DM-LDH could significantly improve the fire resistance of EVA composites.In summary, two novel acid-intercalated LDH (SA-LDH and DM-LDH) were prepared through acid-base reaction and it indicates that the LDHs can improve the flame retardant of EVA composites effectively. |
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