Cure kinetics of vapor grown carbon nanofiber (VGCNF) modified epoxy resin suspensions and fracture toughness of their resulting nanocomposites

Abstract

a b s t r a c tIn 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 asreceived, 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 phenomenological 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.

Effects of graphene oxides on the cure behaviors of a tetrafunctional epoxy resin

“…The influence of carbonbased nano-fillers on the enthalpies of the epoxy cure reaction is different for different nanocomposites. The addition of CNTs [19,20,31] and EG [24] decreased the "H of epoxy, whereas CNF had no pronounced effect on the heat of the TGDDM/DDS cure reaction [32] and silanized and polyaniline modified CNFs increased the "H of epoxy [33,34]. It is believed that the addition of hydroxyl-containing compounds (water, alcohols, phenols, acids) considerably promoted the interaction of epoxy compounds with amines and other nucleophilic reagents [35].…”

Nano-Scale Reinforcing and Toughening Thermoplastics: Processing, Structure and Mechanical Properties

“…In addition, CNF has been applied as the toughening filler of the structural material for resin based composites. (Seyhan et al, 2009) reported that the addition of low content of silanized vapor grown carbon nanofiber (VGCNF) improved the fracture toughness of the epoxy resin by about 12%. They concluded that attachment of epoxide end groups containing silane molecules to surfaces of CNF enhanced the compatibility between CNF and epoxy.…”

Effects of graphene nanoplatelets and graphene nanosheets on fracture toughness of epoxy nanocomposites

“…[11][12][13] In addition, many studies concerning the effects of carbon nanostructures on mechanical and fracture behaviour of thermosetting polymers had reported a notable change in fracture resistance of nanocomposites with lower filler contents in comparison with silica or clay. [14][15][16][17][18] Modification of polymer matrices with graphene platelets (GPs) as reinforcement has opened a new path towards manufacturing advanced materials. 19,20 A GP consists of several single graphene layers with a usual stack thickness around 3 to 80 nm.…”