Thermo-physical characterisation of epoxy resin reinforced by amino-functionalized carbon nanofibers S.G. Prolongo * , M. Campo, M.R. Gude, R. Chaos-Morán, A. Ureña Dpt. Ciencia e Ingeniería de Materiales, Universidad Rey Juan Carlos, 28933 Móstoles, Madrid, Spain article info Article history: Received 19 June 2008 Received in revised form 1 September 2008 Accepted 21 October 2008 Available online 29 October 2008 Keywords: A. Carbon nanofiber A. Nanocomposite A. Polymer-matrix composites (PMCs) B. Thermal properties B. Thermomechanical properties abstract Epoxy/carbon nanofibers (CNFs) composites with different proportions of CNFs have been synthesised. In order to improve the CNFs dispersion into epoxy matrix, the nanofibers were functionalized with amino groups. The effect of the content and the functionalization of the nano-filler on the morphology of nano- composite structure has been studied by optical and electron microscopies. It has been found that the CNFs dispersion is enhanced with the functionalization process up to nanofibers contents of 1 wt%. It has been also found that reached dispersion level markedly affects to the physical and thermo-dynamical mechanical properties of the epoxy nanocomposites. The addition of CNFs causes an important increase of the coefficient of thermal expansion and the glassy storage modulus of nanocomposites but the a-relaxation temperature decreases. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Carbon nanostructures, nanotubes and nanofibers, present no- vel combinations of mechanical and electrical properties. They have high strength and flexibility, extraordinary elastic modulus, high thermal and electrical conductivity and low density [1]. The introduction of these nanostructures as structural reinforcements into polymer matrices may improve their mechanical properties, increasing at the same time the electrical conductive properties of the material [2]. These nanocomposites can be applied for aero- space, electronic devices and many other industrial applications. Therefore, researches on carbon nanoreinforcements/polymer nanocomposites have actually become a key topic in the field. However, the expected spectacular results have not been founded yet [3–6]. It has been well recognized that several fundamental changes in the composites processing must be carried out in order to enable applicable reinforcement by carbon nanotubes and nanofibers. Poor dispersibility and chemical inertness of as-syn- thesised carbon nanostructures are the main processing limita- tions [2,3,7]. When the carbon nanoreinforcements are mixed into a poly- meric matrix, they spontaneously tend to bundle together, which makes their dispersion more difficult. Many research efforts have been carried out to achieve a homogeneous dispersion, including the use of ultrasonication, high shear mixing, aid of sulfactants, alignment, among others [8–12]. On the other hand, the weak interfacial bonding between nanoreinforcement and matrix limits the load-transfer ability. To enhance the stiffness and strength of polymeric matrix is necessary the efficient transfer of stress from polymer matrix to the nanoreinforcements. Typically, the nanore- inforcements are covalent functionalizated through reactive linker molecules [3,5–8,13]. Chemical reaction between linker and matrix functional groups can provide carbon/matrix interfaces of high covalent integrity. Rodriguez [14] reported that graphitic carbon nanofibers (CNFs), particularly those having the platelet or herringbone struc- tures, have edge-site carbon atoms at external surface graphite layer, which are especially suitable for covalent functionalization. Lukehart and co-workers [7] published a successful synthesis pro- cedure in steps to functionalize CNFs; it was based on the surface oxidation, acylation and finally amino-functionalization of carbon nanofibers, providing a highly functionalized CNFs. The final objective of the present work is to obtain a homo- geneous dispersion of CNFs into an epoxy network as well as producing a strong interface between the fillers and polymer matrix by means of CNFs functionalization. We applied the Lukehart’s procedure of CNFs funtionalization, optimizing the experimental conditions [15] and using as reactive linker 4,4 0 - methylenedianiline (DDM), which is the same crosslinker used for the epoxy curing reaction. Also, several dispersion tech- niques have been tested in order to get a homogeneous disper- sion. We study the effect of CNFs functionalization and nanoreinforcement content added on the physical, thermal and mechanical properties of the epoxy resin. The presence of voids and other kinds of discontinuities was analysed by density 0266-3538/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2008.10.018 * Corresponding author. Tel.: +34 91 488 80 83; fax: +34 91 488 81 50. E-mail address: silvia.gonzalez@urjc.es (S.G. Prolongo). Composites Science and Technology 69 (2009) 349–357 Contents lists available at ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech