Isothermal Crystallization Kinetics of Polypropylene Latex–Based Nanocomposites with Organo-Modified Clay LULJETA RAKA, 1 ANDREA SORRENTINO, 2 GORDANA BOGOEVA-GACEVA 3 1 Department of Chemistry, Faculty of Natural Sciences and Mathematics, State University of Tetovo, 1200 Tetovo, Macedonia 2 Department of Chemical and Food Engineering, University of Salerno, I-84084 Fisciano, Salerno, Italy 3 Faculty of Technology and Metallurgy, St. Cyril and Methodius University, 1000 Skopje, Macedonia Received 7 March 2010; revised 27 April 2010; accepted 25 May 2010 DOI: 10.1002/polb.22069 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The effect of organo-modified clay (Cloisite 93A) on the crystal structure and isothermal crystallization behavior of isotactic polypropylene (iPP) in iPP/clay nanocomposites pre- pared by latex technology was investigated by wide angle X- ray diffraction, differential scanning calorimetry and polarized optical microscopy. The X-ray diffraction results indicated that the higher clay loading promotes the formation of the b-phase crystallites, as evidenced by the appearance of a new peak cor- responding to the (300) reflection of b-iPP. Analysis of the iso- thermal crystallization showed that the PP nanocomposite (1% C93A) exhibited higher crystallization rates than the neat PP. The unfilled iPP matrix and nanocomposites clearly shows double melting behavior; the shape of the melting transition progressively changes toward single melting with increasing crystallization temperature. The fold surface free energy (r e ) of polymer chains in the nanocomposites was lower than that in the PP latex (PPL). It should be reasonable to treat C93A as a good nucleating agent for the crystallization of PPL, which plays a determinant effect on the reduction in r e during the isothermal crystallization of the nanocomposites. The activa- tion energy, DE a , decreased with the incorporation of clay nanoparticles into the matrix, which in turn indicates that the nucleation process is facilitated by the presence of clay. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1927–1938, 2010 KEYWORDS: crystallization; nanocomposites; organoclay; poly- (propylene) (PP) INTRODUCTION Polymer/clay nanocomposites (PCNs) have attracted great research attention in recent years because of their significant improvement in physical properties over the neat polymer and conventional composites and improved mechanical properties (stiffness and strength). 1–3 Because of the platelet orientation, PCN also show dimensional stability in two dimensions instead of one known for isotropic fillers. Furthermore, in spite of their submicrometer lateral size, clays are only 1 nm thin and when single layers are dis- persed in a polymer matrix the resulting nanocomposite is optically clear in the visible region. 1 Commercially, PCNs have been used for their ability to improve flame retardancy of the polymer, to reduce gas and liquid permeability com- bined with a reduction of solvent uptake. 4–7 Isotactic poly- propylene (iPP)/clay nanocomposite is among the pioneer researched nanocomposites because iPP is one of the most widely used polyolefins, and its properties are greatly affected by the dispersion of clay in the polymer. 8 As it was recently shown that the newly developed latex (Scheme 1) technology offers an improved interfacial behav- ior, 11 the properties of nanocomposites associated with the addition of small fraction of nanoparticles/filler in the poly- mer matrix are strongly influenced by the nature of clay/ matrix interface. 9,10 Extensive research has shown that the morphology of iPP in fiber/filler-reinforced composites as well as its crystallization and melting behavior are affected by the presence of rein- forcing fibers (carbon, glass, polyethylene terephthalate, etc.). 12,13 The addition of different nanofillers (such as car- bon nanotubes and layered silicates) can induce enhanced nucleation in the matrix and thus changes in crystallization kinetics as well. 11,14,15 The relationship between crystalliza- tion kinetics and processing conditions of thermoplastic composites is very important for the optimization of the pro- cess and the properties of the end product. Research on the polymer crystallization can be carried out under isothermal and nonisothermal conditions, 16 and the analysis of the over- all crystallization rate under isothermal crystallization is gen- erally accomplished with the use of Avrami equation, which is valid at least for early stages of the process. 17 In the last few years, there have been many reports concern- ing crystallization behavior and morphology development under isothermal condition of polypropylene (PP)/clay nano- composites. 2,18–24 However, the effect of montmorillonite (MMT) on the crystallization behavior of iPP is still somehow controversial. Most researchers 22–24 observed an increase in crystallization rate, whereas others found that the filler slowed it down, 24,25 or had no (or had a minor) effect on Correspondence to: L. Raka (E-mail: luljeta.raka@unite.edu.mk) Journal of Polymer Science: Part B: Polymer Physics, Vol. 48, 1927–1938 (2010) V C 2010 Wiley Periodicals, Inc. CRYSTALLIZATION KINETICS OF PPL-BASED PNCS, RAKA, SORRENTINO, AND BOGOEVA-GACEVA 1927