Synergistic effect of expandable graphite, melamine polyphosphate and layered double hydroxide on improving the fire behavior of rosin-based rigid polyurethane foam

Abstract

The halogen-free flame retardant rosin-based rigid polyurethane foams were successfully prepared based on renewable rosin polyester polyol, intumescent flame retardants (such as expandable graphite and melamine polyphosphate) and layered double hydroxide. The morphology, thermal conductivity, mechanical property, thermal stability, flame retardancy and fire behaviors of all RPUFs were comprehensively investigated. Furthermore, potential synergy between layered double hydroxide (LDH), expandable graphite (EG) and melamine polyphosphate (MPP) on fire behavior of rosin-based RPUF has been investigated in detail. XRD results showed that LDH is exfoliated and well dispersed in rosin-based RPUF. The results of SEM and thermal conductivity tests showed that adding intumescent flame retardants (such as EG and MPP) or further adding LDH into RPUF does not have significant influence on the cell structure and thermal conductivity of rosin-based RPUF. The results of TGA showed that adding EG, MPP or further adding LDH into RPUF decreases the initial decomposition temperature and the second-stage maximum-rate decomposition temperature of RPUF, while increases the char residue of RPUF at high temperature whether under N2 atmosphere or air atmosphere. Furthermore, it is noteworthy that simultaneously adding EG, MPP and LDH into RPUF can significantly improve the flame retardancy, mechanical property and fire behavior of rosin-based RPUF. The LOI value of EG10/MPP10/LDH3.0/RPUF sample increases from 19.1 to 28.0% compared to that of pure RPUF. The compressive strength and specific compressive strength (compressive strength/density) for EG10/MPP10/LDH3.0/RPUF sample in parallel direction increase about 8.3% and 7.1% compared to that of pure RPUF, respectively. The cone calorimeter test results showed that simultaneously adding EG, MPP and LDH into RPUF can significantly decrease the heat release rate (HRR), total heat release (THR) and smoke emission behavior of RPUF sample. The average heat release rate (Av-HRR) and total heat release (THR) decrease about 32.5% and 5.2% compared to that of pure RPUF, respectively. The average smoke production rate (Av-SPR), average rate of smoke release (Av-RSR), average specific extinction area (Av-SEA), total smoke release (TSR) and CO/CO2 weight ratio of EG10/MPP10/LDH3.0/RPUF sample decrease about 26.9%, 25.5%, 2.7%, 0.8% and 16.7% compared to that of pure RPUF, respectively. These test results indicating that LDH has synergistic effect with intumescent flame retardants (such as EG and MPP) on improving the fire behavior of rosin-based rigid polyurethane foam.