Spherulite nucleation in isotactic polypropylene based nanocomposites with montmorillonite under shear R. Nowacki a , B. Monasse b , E. Piorkowska a, * , A. Galeski a , J.M. Haudin b a Department of Polymer Physics, Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90 363 Lodz, Poland b Ecole des Mines de Paris, Centre de Mise en Forme des Materiaux, UMR CNRS 7635, BP 207, 06 904 Sophia Antipolis, France Received 3 November 2003; received in revised form 11 March 2004; accepted 5 April 2004 Available online 18 May 2004 Abstract The crystallization of nanocomposites of isotactic polypropylenes with organo modified montmorillonite compatibilized by maleic anhydride grafted polypropylene was studied by light microscopy in isothermal conditions in quiescent state and in shear. The isothermal and nonisothermal crystallization of the composites was also investigated by DSC method. Only weak nucleation activity of montmorillonite was observed during crystallization in static conditions. The clay nucleation activity was greatly enhanced in shear-induced crystallization and resulted in a drastic decrease of spherulite sizes. In nanocomposite films crystallized isothermally the intense nucleation of isotactic polypropylene spherulites was observed when the polymer was forced to flow to compensate the volume shrinkage due to crystallization. It was also found that the presence of a glass support enhances spherulite nucleation in nanocomposites which is caused possibly by shear due to a difference in thermal shrinkage of a polymer matrix and a glass support. q 2004 Elsevier Ltd. All rights reserved. Keywords: Polypropylene based nanocomposites; Montmorillonite; Nucleation under shear 1. Introduction Nanocomposites of polymers with montmorillonite (MMT) are recently a subject of intense investigations. The addition of exfoliated and well dispersed nano-clay, enhances the barrier properties and reduces flammability [1–4]. Usually the presence of nano-clay platelets influ- ences also mechanical properties [4–6]. Nanocomposites with MMT based on isotactic polypropylene (iPP) were also obtained and studied because of the industrial importance of this polymer. The routes to obtain iPP based nanocompo- sites with MMT and the description of material properties were recently reviewed in Ref. [7]. The methods to obtain iPP nanocomposites by melt mixing of organo-modified MMT with a compatibilizer—polypropylene grafted with maleic anhydride (PP-MA) [8] and to use anhydrides— modified propylene oligomers as compatibilizers for iPP/ MMT system [9] were reported. Since the properties of semicrystalline polymers depend on their crystalline structure, the crystallization and the morphology of iPP based nano-clay composites prepared by different methods were investigated [5,6,10 – 13]. The crystallization kinetics of neat polymers is deter- mined by the spherulite nucleation and growth rate. The elevation of nonisothermal crystallization peak temperature due to the presence of MMT was found in composites prepared by melt blending of organo-modified MMT with iPP [10,12]. The nucleation effect of MMT during isothermal crystallization was observed in both PP-MA/ MMT [5] and PP/PP-MA/MMT [13] systems and also in PP/ MMT nanocomposites synthesized by intercalation polym- erization [11]. Svoboda et al. [6] found the acceleration of isothermal DSC crystallization only in PP/PP-MA/MMT systems containing the clay tactoids while no MMT nucleation ability in systems with well dispersed clay was observed. Pozsgay et al. [12] demonstrated that the ability of MMT to nucleate iPP crystallization depends on clay deposit and the organo-treatment of clay; the latter acting not by the modification of the clay surface tension but by the alteration of interlayer distance. They concluded that the nucleation occurs not on the surfaces but rather in the interlayers of clay particles and attributed the nucleating 0032-3861/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2004.04.058 Polymer 45 (2004) 4877–4892 www.elsevier.com/locate/polymer * Corresponding author. Tel.: þ 48-42-681-89-52; fax: þ 48-42-684-71- 26. E-mail address: epiorkow@bilbo.cbmm.lodz.pl (E. Piorkowska).