Polylactide (PLA) nanocomposites with improved mechanical and barrier properties are of growing industrial interest and therefore required green modified montmorillonites (gm-MMTs) to meet the expectation of totally biosourced material. In this study, ulvans that are polysaccharides and glycoproteins extracted from seaweed are used as surfactants to achieve intercalated clays. The effect of this gm-MMT (ALL350) on the crystallization kinetics of PLA was compared to Cloisite 30B, and pristine MMT was taken as a reference. Rheology, differential scanning calorimetry, and transmission electronic microscopy experiments were performed to better understand the effects that dominate the so-called nucleating effect observed in PLA nanocomposites. It was found that two major driving forces explain the efficiency of the ALL350 that enhances PLA nucleation. The first one is the decrease of the interfacial energy and the second is a reduction of the complex viscosity that acts on the induction period. Reduction of both the interfacial energy and the surface friction forces between PLA chains and polysaccharides-treated clay platelets is assumed to facilitate the induction process. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012