Aliphatic polyesters such as polylactide (PLA) currently deserve particular attention in the area of environmentally degradable polymer materials. PLA is produced via polymerization of renewable products, namely lactic acid or lactide. In this work, the synthesis of PLA is done by reactive extrusion via ring opening polymerization of L,L-lactide using a continuous single-stage process which is a fast and an easy method. The resulting PLA is fully characterized by solid state NMR. It is shown that it exhibits properties similar to those of PLA synthesized by the traditional methods. A kinetic model based on a phenomenological approach permits one to describe the polymerization of L,L-lactide. PLA nanocomposites containing multi-wall carbon nanotube (MWNT) are also prepared by reactive extrusion. Reaction to fire of PLA nanocomposite shows a slight improvement of the flame retardancy. The nanodispersion characterized by transmission electronic microscopy (TEM) is acceptable but should be improved to obtain the best flame retardancy. Copyright © 2010 John Wiley & Sons, Ltd.