Flame retardant properties and mechanism of an efficient intumescent flame retardant PLA composites

The charring agent (CNCA-DA) containing triazine and benzene rings was combined with ammonium polyphosphate (APP) to form intumescent flame retardant (IFR), and it was occupied to modify polylactide (PLA). The flame retardant properties and mechanism of flame retardant PLA composites were investigated by the limited oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis, microscale combustion calorimetry, scanning electron microscopy, laser Raman spectroscopy analysis and X-ray photoelectron spectroscopy. The analysis from LOI and UL-94 presented that the IFR was very effective in flame retardancy of PLA. When the weight ratio of APP to CNCA-DA was 3:1, and the IFR loading was 30%, the IFR showed the best effect, and the LOI value reached 45.6%. It was found that when 20wt% IFR was loaded, the flame retardancy of PLA/IFR still passed UL-94V-0 rating, and its LOI value reached 32.8%. The microscale combustion calorimetry results showed that PLA/IFR had lower heat release rate, total heat release, and heat release capacity than other composites, and there was an obvious synergistic effect between APP and CNCA-DA for PLA. IFR containing APP/CNCA-DA had good thermal stability and char-forming ability with the char residue 29.3% at 800 degrees C under N-2 atmosphere. Scanning electron microscopy observation further indicated that IFR could promote forming continuous and compact intumescent char layer. The laser Raman spectroscopy analysis and X-ray photoelectron spectroscopy analysis results indicated that an appropriate graphitization degree of the residue char was formed, and more O and N were remained to form more cross-linking structure. Copyright (c) 2016 John Wiley & Sons, Ltd.