Synthesis of organo-modified α-zirconium phosphate and its effect on the flame retardancy of IFR poly(lactic acid) systems

Novel intumescent flame-retardant poly(lactic acid) (PLA/IFR)/organo-modified α-zirconium phosphate(OZrP) nanocomposites were prepared via incorporation of charring agent (CA), ammonium polyphosphate (APP) and OZrP into PLA. OZrP was synthesized directly by a solvent thermal method. The morphological characterization of PLA/IFR/OZrP nanocomposites was conducted by wide angle X-ray diffraction (WXRD) and transmission electron microscopy (TEM). The effect of the OZrP on flame retardancy and the thermal stability of PLA/IFR composites were studied by thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter test. The TGA data illustrated that the OZrP could increase the residue and significantly improve the flame retardancy of PLA/IFR/OZrP nanocomposites showing an excellent synergistic effect. The addition of OZrP to the flame-retardant PLA increases the LOI and enhances the UL-94 rating. Cone calorimeter tests gave clear evidence that the incorporation of OZrP into PLA/IFR composites resulted in the significant reduction of the heat release rate (HRR), low total heat release (THR) and high amount of char residues during combustion. The flame-retardant mechanism of PLA/IFR/OZrP nanocomposites may correspond to the intumescent flame-retardant mechanism and catalyzed carbonization mechanism caused by OZrP.