The combined effect of epoxy nanocomposites and phosphorus flame retardant additives on thermal and fire reaction properties of fiber-reinforced composites

This study investigates the thermal stability of an aerospace grade epoxy resin containing a silicate-based nanoclay modified by an organophosphorus moiety (vinyl triphenyl phosphonium bromide; VTP), double-walled carbon nanotubes (DWCNTs) and/or conventional phosphorus containing flame retardants (FRs) at weight fractions up to 20% using thermogravimetric analysis (TGA). When FR additives (15 wt%) or VTP containing nanoclay (5 wt%) are used independently, the overall thermal stability enhancement of the epoxy resin follows the order; ammonium polyphosphate (APP) > nanoclay VTP > resorcinol bis-(diphenyl phosphate) (RDP) > tris-(tribromoneopentyl) phosphate (TBP). The addition of DWCNTs alone did not significantly alter the thermal stability of the epoxy resin matrix. The concomitant addition of VTP together with RDP, APP, and TBP at a cumulative weight fraction of 20% led to synergistic improvements in the thermal stability of the resin. The fire reaction properties of the glass fiber-reinforced laminates prepared from modified resin formulations were measured under cone calorimetry conditions at an incident heat flux of 50 kW/m2. The addition of conventional FRs with or without the nanoclay significantly reduced the peak value heat release rate and total heat release relative to the control sample. DWCNTs alone did not show a significant effect on the fire reaction properties of the epoxy resin composites. The burning behavior of the flame-retarded samples as evaluated by cone calorimetry correlated very well with TGA and differential thermal analysis (DTA) data. The depolymerization intensity as measured from DTA data agreed with PHRR from cone calorimetry while the TTI showed a direct correlation to the onset of thermal degradation as determined from TGA data. According to a fire risk assessment based on cone calorimetry data, nanocomposites containing APP achieved the highest fire safety rating.

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