Polylactide (PLA) was modified physically by filling with inorganic additives-organomodified particles of clay, unmodified particles of clay as well as with a plasticizer-poly(ethylene glycol). The PLA-based systems were prepared by melt blending of PLA with other components. Combination of PLA with organomodified clay particles formed nanocomposite with intercalated nanostructure, while introducing microparticles led to microcomposite, respectively. The clay concentration was maintained at 3 wt% in the both systems. Additionally unfilled PLA, plasticized PLA and plasticized nanocomposite were prepared under the same blending conditions. For plasticization, 10 wt% of poly(ethylene glycol) was used. Two groups of the PLA samples and PLA-based systems featured by starting amorphous structure or semicrystalline structure were considered, respectively. The structure, thermal behavior, thermo-optical properties and dynamic mechanical response of the PLA-based systems were investigated and compared with unfilled PLA of the same thermomechanical history and with the neat (unprocessed) PLA. The influence of the composition and thermal treatment on the structure and physical properties of the considered samples was determined. The effect of aging on the structure and crystallization ability of the PLA material from its glassy amorphous state was evaluated as well. Temperature modulated differential scanning calorimetry, thermo-optical analysis, X-ray diffraction technique, dynamic mechanical analysis (DMTA) were used. (C) 2004 Elsevier Ltd. All rights reserved.