Thermal Degradation And Combustion Behaviors Of Flame-retardant Modified Layered Double Hydrotalcides /Polyethylene Nanocomposites

Layered Double Hydrotalcides(LDH) are considered as a new flame retardant due to their high efficiency, non-toxic and environmental friend. The research aims at improving the flame retardant effects of LDHs by modification with flame retardant and construction of nano-structure in the composites. Accordingly, two kinds of modified LDHs with sodium dodecyl sulfate(SDS) and 2-carboxyl ethyl(phenyl) phosphinic acid(CEPPA) were used to prepare polyethylene(PE) based nanocomposites and intumescent flame retardant(IFR) composites. The structure of PE/LDHs composites was characterized with X-ray diffraction(XRD) and scanning electron microscopy(SEM). The thermal degradation and combustion behaviors were investigated by thermogravimetric analysis(TGA), microscale combustion calorimeter(MCC) and cone calorimeter(CONE). The flame retardant properties of flame retardant composites were evaluated by limiting oxygen index(LDH). The comparative studies were performed to investigate the effects of LDHs on the thermal degradation and combustion behaviors due to their compositions and structure. The attention was paid to understand the effects of modified LDH with flame retardant on the synergistic effect with IFR.The following results were collected.(1) The dispersion of LDHs in PE was found to be related to their structure and interlayer distance. Modified LDHs can form exfoliated structure due to its enlarged interlayer distance and good compatibility with PE.(2) Thermal degradation behaviors of PE/LDHs nanocomposites were found similar to PE. Little charring effects could be found in the nanocomposites with modified LDHs, leading to an increased combustion composition. The peak heat release rate(peak HRR) of nanocomposites decreased greatly. A decreased peak HRR of 42%, 19% and 45% was found in the nanocomposites with LDH, SLDH and CLDH, respectively. A better function of CLDH was revealed on suppressing the HRR.(3) Similar thermal degradation and gas phase combustion behaviors were found in LDH modified flame retardant materials and PE-IFR. The formation of intumescent charring layers was enhanced by LDHs, giving rise to a lower combustion composition. The flame retardant materials with CLDH presented much lower amount of heat and smoke released.(4) A better synergistic effect was revealed between CLDH and IFR, which greatly improved the flame retardant properties of intumescent flame retardant PE. A LOI of 32.5 was shown at the same loading levels of fillers. More compact charring layers with improved barrier effect and thermal stability were suggested to explain the synergistic flame retardant mechanism.