In this study, a novel flame retardant (PMrG) was developed by self-assembling melamine and phytic acid (PA) onto rGO, and then applying it to the improvement of the flame resistance of PLA.
PMrG simultaneously decreases the peak heat release rate (pHRR) and the total heat release (THR) of the composite during combustion, and enhances the LOI value and the time to ignition (TTI), thus significantly improving the flame retardancy of the composite.
The flame retardant mechanism of the PMrG is also investigated.
On one hand, the dehydration of PA and the decomposition of melamine in PMrG generate non-flammable volatiles, such as H2O and NH3, which dilute the oxygen concentration around the combustion front of the composite.
On the other hand, the rGO, melamine, and PA components in PMrG create a synergistic effect in promoting the formation of a compact char layer during the combustion, which plays a barrier role and effectively suppresses the release of heat and smoke.
In addition, the PMrGs in PLA exert a positive effect on the crystallization of the PLA matrix, thus playing the role of nucleation agent.
Conclusions
This study demonstrates a simple and green synthesis method for a novel flame retardant via the self-assembly of melamine and phytic acid (PA) onto the rGO skeleton, and the composition can be adjusted by changing the ratio of rGO, melamine, and PA.
A prepared flame retardant (PMrG) is added into PLA, and it shows the best flame retardant effect on the composite when the ratio of rGO, melamine, and PA is controlled at 1:1:5 (PMrG-3).
When 10 wt% PMrG-3 is added, the obtained PMrG-3/PLA composite exhibits greatly reduced pHRR (decreased by 35.3%) and THR (decreased by 21.7%) values, and the TTI is increased from 46 s to 59 s.
In addition, the LOI value is increased from 19% to 25%, indicating the excellent flame retardant effect of PMrG-3 on PLA.
The improved flame-retardant performance of PMrG-3/PLA composites is attributed to the synergistic effect of the rGO, melamine, and PA components in PMrG, which promote the formation of a compact char layer during the combustion, effectively suppressing the release of the heat and smoke.
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