Date of Award
Doctor of Philosophy in Chemical Engineering (PhD)
College, School or Department Name
Department of Chemical Engineering
Julia A. King
Due to their high specific stiffness, carbon-filled polymer composites are commonly used in the construction of structural components of subsonic fixed-wing aircrafts, such as the fuselage and control surfaces. In this work, neat epoxy (EPON 862 with EPIKURE Curing Agent W) was fabricated along with 1- 6 wt% of three types of GNP available from XG Sciences Inc. and 1-4 wt% of another type of GNP available from Asbury Carbons added to epoxy. The curing cycle for this epoxy was 121 °C for 2 hours followed by 177 °C for two hours.
GNP are short stacks of individual layers of graphite that are newly developed and available at a low cost. XG Sciences Inc. xGnP®-M-15 has a platelets diameter of 15 μm and a thickness of 7 nm. xGnP®-M-5 has a diameter of 5 μm and a thickness of 7 nm. The specific surface area for both M-grades is 130 m2/g. xGnP®-C-300 has a diameter of 2 μm and a thickness of 2 nm with a specific surface area of 300 m2/g. Asbury Carbon’s TC307 GNP has a particle size <1 μm diameter and ~8 layers (1.1 nm) thick and a specific surface area of 350 m2/g.
Development of good dispersion techniques was the most important contribution of this project. Proper dispersion is very important for obtaining a good composite. For each of the four types of GNP used in this study, a unique dispersion method was developed. High shear mixing was used in combination with sonication to exfoliate the GNP and disperse it into the epoxy matrix. An optical microscope was used to monitor the dispersion during mixing progression.
The composites were tested for their mechanical properties using typical macroscopic tensile testing, nanoindentation, and dynamic mechanical analysis. The addition of any of the four types of GNP resulted in an increase in the modulus (stiffness). The modulus can be predicted using the Halpin-Tsai model. The Halpin-Tsai model takes into account the mechanical properties of the polymer and the filler and also the filler geometry. The 2D randomly oriented filler Halpin-Tsai model was useful for predicting the modulus for xGnP®-M-15 in epoxy and xGnP®-M-5 in epoxy, this was confirmed visually through microscopy. The 3D randomly oriented filler Halpin-Tsai model predicted the modulus well for the xGnP®-C-300 and the TC307, microscopy visually confirmed that the filler was oriented in all three planes.
From the mechanical properties, one type of GNP was chosen for use in a unidirectional carbon fiber composite. The continuous carbon fiber composites were tested via macroscopic tensile tests. The GNP chosen did not have an effect on the composite’s axial modulus, but increased the transverse modulus. The carbon fiber’s mechanical properties dominate over the GNP/epoxy properties in the axial direction. As far as current literature available, continuous carbon fiber has never been used as a reinforcement for GNP/epoxy composites.
Klimek-McDonald, Danielle René, "MECHANICAL PROPERTIES OF GRAPHENE NANOPLATELET/EPOXY COMPOSITES", Dissertation, Michigan Technological University, 2015.