Studies On The Cure Behaviors Of Epoxy/Graphite Oxide (GO) Nanocomposites

As the main raw material of graphene, graphite oxide (GO) contains plenty of oxygen functionalities, such as hydroxyl and epoxy groups, which will influence the cure behavior of epoxy. In this thesis, GO prepared by Hummers method incorporated into high-performance tetraglycidyl-4,4'-diaminodiphenylmethane (TGDDM) with 4, 4'-diaminodiphenylsulphone (DDS) as a curing agent by sonication. The cure kinetics, thermal stability and morphology of the epoxy nanocomposites were studied.The structure of GO were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results showed that the conjugated structure of graphite was destroyed after oxidation, forming randomly aggregated, thin, crumpled chips closely associated with each other, so disordered degree increased from 0.07 to 0.99, the distance between sheets increased from 3.35A to 7.27A. XPS results indicated that the surface of GO contains high percentage of oxygen functionalities. Furthermore, the narrow, asymmetric Cls band characteristic of pristine graphite transformed into a complex band showing three maxima for GO, as expected, due to the high percentage of oxygen functionalities, which are the C in C=C bonds, C-O bonds and the carboxylate carbon (O-C=O). FT-IR results further confirmed that hydroxyl. carboxyl and cyclic epoxide groups were on the surface of GO, while the results of TGA showed that 51.2% weight of GO losted in the temperature of 700℃. And observation of SEM found that disordered degree of graphite increased after oxidation.The influence of graphite oxide on the isothermal and dynamic (non-isothermal) cure behavior of TGDDM/DDS systems were studied by differential scanning calorimetry (DSC). Furthermore, the thermal stability and morphology of epoxy/GO nanocomposites were investigated by TGA and SEM. Isothermal DSC results showed that time to maximal reaction rate (tp) decreased and the initial reaction rate ((da/dt)o) increased with the increase of GO contents, indicating that the graphite oxide catalyzed the cure reaction of epoxy resin. Diffusion control-modified Kamal model was used to characterize the isothermal cure kinetics of epoxy/GO nanocomposites. The activation energy for the initial stage of the reaction (E1) obtained by Kamal's model decreased first and then increased while the activation energy for the reaction after the initial autocatalytic stage(E2) slightly decreased with the increase of GO contents. Good agreement between experimental data and the autocatalytic model modified with diffusion control was found over the whole curing temperature range.The non-isothermal DSC results showed that the initial reaction temperature (Ti) and exothermal peak temperature (Tp) decreased whereas the conversions of reaction (a) increased with the increase of GO contents, and the activation energy (Ea) decreased first and then increased when a<0.2 whereas Ea decreased gradually when a>0.5 with the increase of GO contents based on the Friedman method, while Ea decreased first and then increased from both the Kissinger and FWO method. So conclusion can be made that the incorporation of GO can accelerate the cure reaction of TGDDM/DDS system at lower GO content in the initial reaction, and the accelerated effect can be enhanced with the increase of GO contents in the latter process of reaction. Therefore, it can be concluded that different types of oxygen functionalities on the surface of GO significantly catalyzed the cure reaction of epoxy. Furthermore, the catalytic effect increased with the increase of GO contents.TGA and differential thermogravimetry (DTG) results showed that the addition of GO significantly decreased the initial decomposition temperature of epoxy, which suggested that the existence of GO reduced the thermal stability of epoxy. SEM results showed that GO was uniformly dispersed in the epoxy due to the existence of epoxide groups on the surface of GO.