59th Annual Report on Research 2014

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Reports: DNI1052308-DNI10: Graphene-Integrated Durable Rubber Sealants for Petroleum Exploration

1. Experimental The graphene was produced from graphite by the modified Brodie’s method. 1 L of 1 mg/ml graphene oxide (GO) solution was mixed with 50M of N-(3-Dimethylaminopropyl)-N0-ethyl carbodiimide hydrochloride (EDAC) by stirring for 10 min and then 100 ml of allylamine was added. The resultant mixture was vacuum filtrated and dried at 70 °C to obtain the allyl functionalized graphene oxide powder (AGO). The AGO was further reduced by hydrazine to obtain reduced AGO (RAGO), as illustrated in Fig. 1. The allylamine is attached onto graphene through the carboxyl group and the allyl groups are present after the reduction.
Subsequently, 350 g FKM was mixed with 5.25 g (1.5 wt%) graphene nanoparticles, 8.75 g (2.5 phr) peroxide and 10.5 g (3 phr) Ca(OH)₂ by an open twin-roll miller at 80 °C. The mixed pastes were compression molded and cured at 177 °C, 5 MPa by a hot press machine according to ASTM D3182.   2. Characterization The Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra of the as-synthesized graphene nanosheets were illustrated in Fig. 2. The peaks at around 1360 cm^-1,1690 cm^-1 and 3400 cm^-1 indicate that only GO and AGO contained oxygen-containing groups. The attachment of allylamine on AGO and RAGO was confirmed by the peaks at 820 cm^-1 and 1610 cm^-1, which represent the primary amine groups and the stretching of amine groups, respectively. The peak at ~399 eV in Fig. 2(b) further validates the presence of nitrogen in AGO and RAGO. The C1s XPS spectra proved that both AGO and RAGO showed weakened signals at ca. 289.2 eV in contrast with GO, which indicates the presence of the covalent bonds between allylamine and graphene.
The thermogravimetric analysis (TGA) results in Fig. 3 indicated the excellent thermal stability of RGO and RAGO at the vulcanization temperature of 177 °C while GO and AGO are not suitable nanofillers for high temperature utility. The influence of the functionalized graphene on the vulcanization kinetics in FKM was also studied through the rheology curves of all the nanocomposite samples at 177 °C by an oscillating disc rheometer (ODR) according to ASTM D2084. As shown in Fig.3(b), the presence of RAGO in FKM compound provided the highest values of maximum torque, as well as the lowest values of scorch time and the optimum cure time, suggesting an accelerated vulcanization of FKM.       The vulcanization kinetics of the nanocomposites at different temperatures was further analyzed as shown in Fig.4.(a). The degree of curing (a) and the values of specific rate constant K for the control samples were calculated through linear multiple regression analysis. The plots of conversion rate (da/dt) versus the degree of conversion (a) were summarized in Fig. 4(b). As the temperature increased, both the peak height of the conversion curve and the peak position were increased. The activation energy Ea required for vulcanization was subsequently calculated by the Arrhenius equation, as shown in Fig. 4(c). The addition of RAGO dramatically decreased the Ea of the nanocomposites from 120.97 kJ/mol to 56.59 kJ/mol, which indicated that the allyl groups on the graphene accelerated the vulcanization by decreasing the Ea.     Fig. 5 shows the tensile test results of the cured FKM composites. The tensile strength of RAGO/FKM is increased by 70.4% at 175 °C, 45.6% at 125 °C, and 26.3% at 75 °C when compared to that of the control. It is mainly accredited to the high modulus/strength and large aspect ratio of graphene. Moreover, the enhanced covalent bonding between allyl functionalized graphene and the FKM matrix further contribute to a higher tensile strength.     3. Results and Discussion In this project, thermally stable graphene was achieved with allyl functionalization and was incorporated into FKM by a radical trap enhanced free radical reaction. The rheometer test, equilibrium swelling, and tensile test indicated that allyl functionalization of graphene significantly improved the performance of FKM nanocomposites. The vulcanization kinetics analysis revealed that the activation energy was reduced by half after covalently bonding allyl functionalized graphene. This work provides an effective functionalization method to incorporate graphene into polymers through a free radical reaction.   4. Impact of this research The research will impact the further development and applications of graphene in petroleum exploration materials. (1) A cost-effective processing method using ultrasonication and co-coagulation technique was employed to fabricate graphene-integrated FKM nanocomposites. (2) The effects of processing, surface modification, graphene fractions, and curing agent on the crosslinking network structure and properties of FKM nanocomposites were revealed and will be further optimized by material/process design. (3) A novel graphene/FKM nanocomposite with superior high-temperature mechanical properties, and gas-/liquid-barrier properties is anticipated to bring a breakthrough in next-generation gas/liquid sealant materials that are able to stand up in harsh environments for petroleum exploration. The results of this research will advance the PI’s career path by dissemination through annual reports to ACS, presentations in ASME, ACS, invited talks/seminars, and journal publications in high-quality academic journals. The funding also helps to improve research infrastructure and build up more experimental data for other potential proposals. The research achievements have been incorporated into the graduate course ME5340 (Elasticity) and ME6330 (Bio/Nano-materials). 1 Phd student is supported by this grant and works toward his dissertation. Till now, two journal papers have been published and the other two are under reviews. An undergraduate student is also involved in this project. Those students gained intensive experience in nanotechnology for petroleum engineering materials and will have better opportunities to work in the field of petroleum engineering.