The effect of different organic modified montmorillonites (DK1, DK2, and DK4) based on a novel intumescent flame retardant (IFR) poly(lactic acid) (PLA) system is reported. The IFR system was composed of microencapsulated ammonium polyphosphate and lignin. The morphological characterization of PLA/OMMT nanocomposites was conducted by X-ray diffractometry and transmission electron microscopy. The flame retardant and thermal properties of the composites were evaluated by limiting oxygen index (LOI), vertical burning test (UL-94), and cone calorimeter. From the results, it could be seen that the sample containing DK2 possessed the best flame retardance, such as lower peak heat release rate (pHRR) and higher LOI value. The thermal degradation and gas products of the samples were monitored by thermogravimetric analysis and thermogravimetric analysis infrared spectrometry. Scanning electron microscopy was used to explore the surface morphology of the char residues. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013