Morphology and Crystallization Behavior of the PP/PET Nanocomposites Carmen I. W. Calcagno, 1,2 Cleide M. Mariani, 1 Se ´rgio R. Teixeira, 3 Raquel S. Mauler 1 1 Instituto de Quimica - PGCIMAT, Universidade Federal do Rio Grande do Sul, Av. Bento Gonc ¸alves, 9500, Porto Alegre/RS 91501-970, Brazil 2 CEFET/RS, Av. Copacabana, 100, 93216-120, Sapucaia do Sul, Brazil 3 Instituto de Fisica - PGCIMAT, Universidade Federal do Rio Grande do Sul, Av. Bento Gonc ¸alves, 9500, Porto Alegre/RS 91501-970, Brazil Received 10 May 2007; accepted 14 May 2008 DOI 10.1002/app.28977 Published online 26 September 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Nanocomposites containing polypropylene (PP), PET, and montmorillonite were prepared in a twin- screw extruder. X-ray diffraction, transmission electron mi- croscopy, scanning electron microscopy, atomic force mi- croscopy, polarized optical microscopy, and differential scanning calorimetry were used to characterize the sam- ples. Intercalated and exfoliated morphology were ob- served in the nanocomposites. The PET domains usually presented spherical shapes and they were the start point to PP crystallization. The average diameter and number of PET domains was evaluated. The influence of addition of PP-MA as compatibilizer on PP/PET was investigated. The interconnected morphology was observed in the nano- composite containing PP-MA. The clay located predomi- nantly in the interphase and in the PET phase. The crystallization process was monitored and the PET crystal- lization rate was slower in the nanocomposites. V V C 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 29–36, 2009 Key words: nanocomposite; PP/PET blend; crystallization INTRODUCTION Polypropylene (PP), is one of the most important type of thermoplastics used in industrial processes. The growth of its importance is attributed to its attractive combination of low cost, low density, and high heat distortion temperature (HDT). However, there are always certain shortcomings in physical and chemical properties that can limit the universal use of any given polymer. Polymer blending is a useful technique to gener- ate materials with specific enhanced properties. The blending of polyolefins with engineering plas- tics is a route to improve the mechanical properties of polymeric materials. Another route that has been widely used is based on the development of nanocomposites. Nanocomposites use low filler content (usually <6%) and show extraordinary advantages in the me- chanical, thermal, optical, and physicochemical properties when compared to the pure polymer or the conventional composites (with micrometer par- ticles sizes). 1,2 Silicates, like montmorillonite (MMT), have been used for nanocomposites preparation owing to their high aspect ratio (size/thickness) and unique intercalation/exfoliation characteristics. The improvement in nanocomposites properties is directly correlated with the exfoliation/dispersion of the nano- clay layers within the polymeric matrix. There are sev- eral techniques used for dispersing clay at a nanoscopic scale, as in situ intercalative polymerization; solvent swollen polymer (solution blending); or melt intercala- tion method, as described in recent reviews. 1–4 The dispersion of the clay into polyolefins was found to be a key step in the preparation of nano- composites. Because of the low polarity of PP, it is difficult to get the exfoliation and homogeneous dis- persion of the silicate layer at the nanometer level in the polymer. Several tentative have been done to obtain polyolefin nanocomposites and most of them result in intercalated morphology. 5,6 Nevertheless, polymer/clay nanocomposites have experienced some success in several kinds of polar polymers and the blending of a polar and an apolar thermoplastic polymer appeared, therefore, to be promising. 7–15 The PP/PET blend development has importance due its potential for some applications in engineer- ing. The addition of PET in PP results in elastic modulus increase and improvement in the mechani- cal properties. 16 However, no study on nanocompo- sites containing these two polymers was found. Most chemically different polymers are immiscible and their blending leads to materials with weak inter- facial adhesion and poor mechanical performances. It is difficult to obtain good dispersion in polymer Journal of Applied Polymer Science, Vol. 111, 29–36 (2009) V V C 2008 Wiley Periodicals, Inc. Correspondence to: R. S. Mauler (mauler@iq.ufrgs.br). Contract grant sponsor: The Conselho Nacional de Desenvolvimento Cientı ´fico e Tecnolo ´ gico-CNPq, Pronex/ FAPERGS.