Materials Chemistry and Physics 118 (2009) 234–242 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys Cure kinetics of vapor grown carbon nanofiber (VGCNF) modified epoxy resin suspensions and fracture toughness of their resulting nanocomposites A.T. Seyhan a,d , Z. Sun a , J. Deitzel a , M. Tanoglu b,∗ , D. Heider a,c a Center for Composite Materials (CCM), University of Delaware, Newark, DE 19716, USA b Department of Mechanical Engineering, Izmir Institute of Technology, 35430 Urla, Izmir, Turkey c Department of Electrical and Computer Engineering, University of Delaware, Newark, DE 19716, USA d Department of Materials Science and Engineering, Anadolu University, Iki Eylul Campus, 26550 Eskisehir, Turkey article info Article history: Received 19 January 2009 Received in revised form 17 May 2009 Accepted 18 July 2009 Keywords: Polymers Nanostrcutures Dynamic scanning calorimetry (DSC) Fracture and toughness abstract In this study, the cure kinetics of Cycom 977-20, an aerospace grade toughened epoxy resin, and its suspensions containing various amounts (1, 3 and 5 wt.%) of vapor grown carbon nanofibers (VGCNFs) with and without chemical treatment were monitored via dynamic and isothermal dynamic scanning calorimetry (DSC) measurements. For this purpose, VGCNFs were first oxidized in nitric acid and then functionalized with 3-glycidoxypropyltrimethoxy silane (GPTMS) coupling agent. Fourier transform infrared (FTIR) spectroscopy was subsequently used to verify the chemical functional groups grafted onto the surfaces of VGCNFs. Sonication technique was conducted to facilitate proper dispersion of as- received, acid treated and silanized VGCNFs within epoxy resin. Dynamic DSC measurements showed that silanized VGCNF modified resin suspensions exhibited higher heat of cure compared to those with as-received VGCNFs. Experimentally obtained isothermal DSC data was then correlated with Kamal phe- nomenological model. Based on the model predictions, it was found that silanized VGCNFs maximized the cure reaction rates at the very initial stage of the reaction. Accordingly, an optimized curing cycle was applied to harden resin suspensions. Fracture testing was then carried out on the cured samples in order to relate the curing behavior of VGCNF modified resin suspensions to mechanical response of their resulting nanocomposites. With addition of 1 wt.% of silanized VGCNFs, the fracture toughness value of neat epoxy was found to be improved by 12%. SEM was further employed to examine the fracture surfaces of the samples. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Incorporation of nanofillers into various types of polymers has aroused great attention in materials science to accomplish multi- functional nanocomposites with enhanced mechanical and thermal properties [1–6]. In this manner, carbon nanofibers (CNFs) with large aspect ratio and surface area hold promise for the develop- ment of novel polymer based nanocomposites [3,4,2,6]. In addition, CNFs possess low cost relative to carbon nanotubes (CNTs). To real- ize, however, the desired ultimate properties in final composite parts requires the enhancement of poor dispersion state of CNFs, as in the case of CNTs, arising from their inert surfaces and huge surface areas [1–7]. Therefore, some chemical functional groups are grafted onto surfaces of CNFs or CNTs to enhance their compatibil- ity with the surrounding matrix resin [1–8]. Oxidation has been the most common reaction for such chemical modifications because it ∗ Corresponding author. Tel.: +90 232750 7806; fax: +90 232750 7825. E-mail address: metintanoglu@iyte.edu.tr (M. Tanoglu). provides a chemical convenience for the conceivable subsequent reactions. More specifically, oxidation reactions generate various functional groups including carboxylic acid, alcohols and ethers. Of all, the most valuable one is carboxylic acid groups. This is because a number of coupling reactions can take place in the presence of carboxylic acid groups, which enables introduction of different types of chemical molecules onto the surfaces of nanofillers [9,10]. However, chemical functional groups grafted onto the surfaces of nanofillers may have some considerable influences on the features of composite processing. In particular, they may alter cure kinet- ics, viscosity and flow behavior of the injected matrix resin in a simultaneous manner [2,6–18]. There have been a number of studies reported in the literature about the influence of nanofillers such as CNTs and CNFs on the cure kinetics of various types of epoxy resins [11–17]. Xie et al. [9,17] investigated the effects of incorporation of CNFs and CNTs on the cure kinetics of epoxy resins by conducting several isother- mal DSC measurements. They concluded that the presence of CNTs within the epoxy resin showed more pronounced effects on the cure kinetic parameters of the corresponding epoxy resin as com- 0254-0584/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2009.07.045