Kaolin–Epoxy-Based Nanocomposites: A Complementary Study of the Epoxy Curing by FTIR and Fluorescence P.D. Castrillo, 1 D. Olmos, 1 J.M. Torkelson, 2 J. Gonza´ lez-Benito 1 1 Dpto. Ciencia e Ingenierı´a de Materiales e Ingenierı´a Quı´mica, Universidad Carlos III de Madrid, Avda, Universidad 30, 28911 Legane´ s, Madrid, Spain 2 Department of Chemical & Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208 This work is focused on the study of the effect exerted by the presence of kaolin on the cure reaction of an epoxy-based polymer, discussing the influence of dif- ferent kaolin pretreatments. During the last few years, the interest on polymer matrix nanocomposite materi- als has sharply increased because generally they show improved properties when compared with those of the neat polymer (without filler). Among this sort of materi- als, polymer clay nanocomposites have been widely studied. However, there are not many works about kaolin-based composites. Although several techniques have been used to monitor the cure process in epoxy- based composites such as Fourier transform infrared spectroscopy (FTIR) or differential scanning calorime- try, only the use of the fluorescent response from a flu- orophore seems to be adequate to monitor the reac- tion exactly at the interfaces at a molecular scale. In this work, FTIR and fluorimetry were used to monitor the cure reaction of the different composite systems at different curing temperatures. The analysis of FTIR experiments revealed that the presence of the rein- forcement clay affects the extent of the cure reaction depending on the nature of its surface. On the other hand, the use of a fluorescent molecule chemically bonded to the reinforcement allows studying the curing exactly at the interface. Finally, with the collected data, a kinetic analysis was done and the results obtained were compared in terms of the technique used and the information source (interface or bulk). At the interface, the activation energy for the epoxy reaction is lower than that carried out in the bulk indicating that the reaction at the interface proceeds via a particular mechanism for which the reaction is favored. It seems that a higher amount of hydroxyl groups is capable of catalyzing the cure reaction. POLYM. COMPOS., 31:781– 791, 2010. ª 2009 Society of Plastics Engineers INTRODUCTION Polymers filled with layered silicates are a kind of nanocomposites that have been extensively studied during the last two decades. In many cases, these materials have shown to have good flame retardant properties, thermal stability, gas barrier properties, and improved same ki- netic analyses mecano-dynamical properties. Most of the research activity in this field has been focused on the study of nanocomposites based on different polymer mat- rices, such as epoxies [1, 2], polystyrene [3, 4], polypro- pylene [5, 6], polyethylene [7], filled with hectorite or montmorillonite [2, 6]. However, although less exten- sively, other layered silicates such as vermiculite [8], ben- tonite [9], and kaolinite [10] have also received some attention. In all cases, the good dispersion of the nano- platelets arising from a full exfoliation of the layered silicates is the most important challenge to achieve the important enhancement of certain properties. However, to study how the inorganic filler specifically interacts with the polymer matrix is a crucial issue to subsequently understand the final performance of this sort of materials. In fact, to know and to understand the possible changes of the polymer matrix appearing at the interface can help to explain the final morphology and, consequently, the final properties of the nanocomposites. Among all the polymer matrices that have been studied in this kind of composites, the epoxy-based thermosets have received an important attention mainly looking for the improvement of several properties such as their fracture toughness and resistance to crack propagation. However, this improvement of properties seems to be very dependent on the degree of exfoliation of the clay [11]. For this reason, in the case of using clays, great efforts must be focused on the complete dispersion of the inorganic filler which should imply the full layers exfolia- tion. This important task can be tackled from two main Correspondence to: J. Gonza´lez-Benito; e-mail: javid@ing.uc3m.es Contract grant sponsor: MEC; contract grant numbers: MAT2004-01347, MAT2007-61607. DOI 10.1002/pc.20860 Published online in Wiley InterScience (www.interscience.wiley.com). V VC 2009 Society of Plastics Engineers POLYMERCOMPOSITES—-2010