Effects of Single-Walled Carbon Nanotubes on the Crystallization Behavior of Polypropylene L. Valentini, 1 J. Biagiotti, 1 J. M. Kenny, 1 S. Santucci 2 1 Materials Engineering Center, Universita ` di Perugia, 05100 Terni, Italy 2 Dipartimento di Fisica, Unita ` INFM, Universita ` dell’Aquila, 67010 Coppito (AQ), Italy Received 25 February 2002; accepted 26 April 2002 Published online 19 November 2002 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/app.11469 ABSTRACT: Polypropylene matrix composites reinforced with single-walled carbon nanotubes (SWNTs) were pro- duced with different nanotube concentrations. The charac- terization of these new materials was performed by differ- ential scanning calorimetry and Raman and Fourier trans- form infrared spectroscopy to obtain information on the matrix–nanotube interaction, on the crystallization kinetics of polypropylene, and especially on the macrostructure and organization of the nanotubes in the composite. On the one hand, the results conﬁrmed the expected nucleant effect of nanotubes on the crystallization of polypropylene, but on the other hand, this effect was not linearly dependent on the SWNT content: there was a saturation of the nucleant effect at low nanotube concentrations. Raman spectroscopy was successfully applied to demonstrating that in the composite ﬁlms, the crystallization kinetics were strongly affected by the distance between the nanotube bundles as a result of a different intercalation of the polymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 708 –713, 2003 Key words: nanocomposites; poly(propylene) (PP); differen- tial scanning calorimetry (DSC); Raman spectroscopy INTRODUCTION Because of the unusual mechanical 1,2 and electronic properties, 3,4 extensive studies have been devoted to the use of carbon nanotubes (CNTs) as nanoﬁbers to improve the performance of a matrix or to achieve new properties. 5–8 One of the advantages of CNTs as reinforcements is their large surface area, which can induce better adhesion with the polymeric matrix, which is an important factor for an effective enhance- ment of the composite properties. 9,10 Among the most versatile polymer matrices, poly- oleﬁns such as polypropylene (PP) are the thermoplas- tics of higher consumption because of their well-bal- anced physical and mechanical properties and their easy processability at a relatively low cost. In PP ma- trix composites, the crystalline morphology of the polymer can be inﬂuenced by the ﬁbers, which can act as nucleant agents inﬂuencing the crystallization pro- cess. Recent developments of nanoﬁller-reinforced composites have shown that it is possible to obtain well-performing materials. 11 To unlock the potential of CNTs for applications in thermoplastic matrix- based nanoﬁller composites, we need to analyze the crystallization behavior and the consequent micro- structure of such polymers to provide useful informa- tion for the design of processing operations. In this work, we investigated the effects of different concentrations of single-walled carbon nanotubes (SWNTs) on the crystalline kinetics and morphology of PP matrix composites. The thermal characterization was performed with differential scanning calorimetry (DSC). The vibrational properties of the composites at several nanotube concentrations were studied with Raman spectroscopy. Fourier transform infrared (FTIR) spectroscopy was then used to examine the possible chemical interactions between the two materials. EXPERIMENTAL A commercially available grade of isotactic polypro- pylene (iPP; melt-ﬂow index = 2.9 dg/min at 190°C and 5 kg, density = 0.90 g/cm 3 ), kindly supplied by Solvay (Brussels, Belgium) under the trade name of Eltex-P HV-200, was used in this work. Nanotubes (SWNTs) were commercially obtained from CarboLex (Kentucky). The material consists of packed bundles of nanotubes with individual diameters equal to 12–20 Å. There are about 30 nanotubes per bundle (with an average bundle diameter of 100 Å) with a length of several micrometers. For the composite production, PP was melt-blended with the addition of several nanotube concentrations speciﬁed as weight percentages in the polymer: 5, 10, 15, and 20%. The temperature of the mixing system was estimated by a thermocouple regulation to 190°C, and the blending time was 10 min. The nonisothermal thermal analysis was performed with a PerkinElmer (Maryland) Pyris 1 differential Correspondence to: J. M. Kenny (kenny@unipg.it). Journal of Applied Polymer Science, Vol. 87, 708 –713 (2003) © 2002 Wiley Periodicals, Inc.