Introduction Biodegradable polymers are growing mainly due to ecological reasons [1–3]. Commercial starch based blends are very useful for the management of post-consumer waste and are used especially for packaging industry [4–6]. Polymeric materials have been filled with several inorganic synthetic and/or natural compounds in order to increase several properties (especially mechanical and impact properties) and decrease others (such as gas permeability) [7–16]. In the case of crystalline polymers, mechanical and physical properties are strongly dependent on the crystal structure and morphology that are related with the crystallization degree. Cyras et al. [4] have studied the effect of natural fibres (sisal) on the crystallization behaviour of MaterBi-Z (polycaprolactone/starch blend). They have found that the Avrami exponent, n, was close to 2 for the matrix and that this exponent remained constant when sisal fibres were incorporated up to 30 mass%. On the other hand, they demonstrated that for a given crystallization temperature, the induction time and the half-time of crystallization in- creased with fibers incorporation (30 mass%). An increase on the half-time of crystallization is related with a decrease on the crystallization rate. Both activation energies (for induction time and for the rate constant) slightly increased when fibres were added. In the case of nanocomposites, investigation of the early stages of crystallization is of particular interest, because of the possible role of clay platelets and tactoids in crystal nucleation. It has been studied that clay particulates greatly affects the crystallization behaviour and morphology of polymer matrix. In several cases, heterogeneous nucleation was observed [15, 17, 18]. Nanoparticles can either increase or decrease the global crystallization rate of a semicrystalline polymer: Fornes et al. [19] have shown that high clay concentrations reduce the rate of crystallization in the case of Nylon 6/MMT nanocomposites. Similar effects have been observed for nanocomposites in other matrices like PCL systems. Di Maio et al. [18] have studied the case of PCL (polycaprolactone)/MMT. They showed that the addition of 0.1% of nanoclay resulted in a reduction of the crystallization half-time to less than 1/2 of that of the pure matrix. The highest crystallization rate was achieved with 0.4% of clay. At higher nanoclay concentration, the crystallization rate started to decrease. Furthermore, besides the influence on nucleation, a retarding effect of the silicate layers on the crystal growth of polymer matrices has been found [19–21]. In the crystallization of extruded PA-6 (polyamide-6)/MMT nanocomposites, the overall crystallization rate decreases with increasing silicate layer content at the highest silicate layer contents, or even over the full silicate layer content range [19]. Another important effect of clay incorporation is the change on the crystallinity degree which is strongly related with final mechanical properties. Strawhecker et al. [22] have shown for PEO that the enthalpy of melting (measured by DSC), showed no strong effect of the silicate loading and/or the crystal- 1388–6150/$20.00 Akadémiai Kiadó, Budapest, Hungary © 2008 Akadémiai Kiadó, Budapest Springer, Dordrecht, The Netherlands Journal of Thermal Analysis and Calorimetry, Vol. 91 (2008) 3, 749–757 ISOTHERMAL CRYSTALLIZATION OF LAYERED SILICATE/STARCH-POLYCAPROLACTONE BLEND NANOCOMPOSITES C. J. Perez, A. Vázquez and V. A. Alvarez * Research Institute of Material Science and Technology (INTEMA), – National University of Mar del Plata (UNMdP) Av. Juan B. Justo 4302, 7600 Mar del Plata, Argentina The isothermal crystallization behavior of layered silicate/starch-polycaprolactone blend nanocomposites was studied by means of differential scanning calorimetry (DSC) measurements. The theoretical melting point was higher for the matrix than for nanocomposites. At low clay concentration, the induction time decreased and the overall crystallization rate increased acting as nu- cleating agent whereas at higher concentrations became retardants. Classical Avrami equation was used to analyze the crystallization kinetic of these materials. n values suggested that clay not only affected the crystallization rate but also influenced the mechanism of crystals growth. An Arrhenius type equation was used for the rate constant (k). Models correctly reproduced the experimental data. Keywords: Avrami equation, biodegradable polymers, clays, crystallization, modeling, nanocomposites * Author for correspondence: alvarezvera@fi.mdp.edu.ar