Abstract:

Objective: The objective of this study was to analyze synergistic flame retardant mechanism of magnesium-aluminum layered double hydroxides(MgAl-LDHs) and melamine phosphate(MP), and to provide theoretical bases of MgAl-LDHs and MP compound flame retardant for fiberboard. Method: The flame retardant performance of medium density fiberboard was tested using oxygen index meter and cone calorimeter. The synergistic effect on heat release performance and smoke generation characteristics of compound flame retardants was performed through synergy ratio of limiting oxygen index (LOI), heat release rate(HRR), total heat release(THR), smoke production rate(SPR) and total smoke release(TSR). Furthermore, the thermogravimetric, fourier infrared spectroscopy and thermogravimetric-fourier infrared spectroscopy combined techniques were used to discuss the condensed phase and gas phase flame retardant mechanisms between MgAl-LDHs and MP. Result: The oxygen index of medium density fiberboard that produced with MgAl-LDHs and MP compound flame retardant was 31.9%. The compound flame retardant did not show a synergistic effect in the calculation of the oxygen index synergy ratio. However, the ratio calculation of cone calorimeter showed a synergistic effect. The pyrolysis analysis showed that the flame retardant effect of compound flame retardant on wood powder was better than that using MgAl-LDHs or MP alone. During the combustion process, MP catalyzed MgAl-LDHs rapid decomposition to release a large amount of water vapor and carbon dioxide, and to absorb the heat of the medium density fiberboard to further reduce the surface temperature. The result led to the combustion difficult to maintain, and simultaneously water vapor and carbon dioxide diluted the combustible gas and oxygen concentration for reducing combustion rate. The flame retardant mechanisms of compound flame retardant were mainly the gas phase flame retardant, and there was not an obvious condensed phase. The gas phase flame retardant was the result of the combined action from a cooling effect and a dilution effect. The compound flame retardant was mainly gas phase flame retardant before 320 ℃ and transformed into condensed phase flame retardant after 380 ℃. Conclusion: The synergistic mechanisms of MgAl-LDHs and MP compound flame retardant shown in three aspects: 1) The decompose temperature range of compound flame retardant was increased and its initial decompose temperature was 198 ℃, meaning that the MgAl-LDHs would decompose in a lower temperature. 2) MgAl-LDHs and MP were released a large amount of water vapor, carbon dioxide and ammonia gas during thermal decomposition, these gas diluted the combustible gas on combustion surface and presented dilution effects. 3) Synergistic effect of MP catalyzed carbon formation and MgAl-LDHs high temperature melting coverage.

Key words: magnesium-aluminum layered double hydroxides (MgAl-LDHs), melamine phosphate (MP), medium density fiberboard, flame retardant, saynergistic effect