Abstract
The objectives of this research are the preparation and characterization of Multi-Walled Carbon NanoTubes (MWCNTs)/Graphite Nanosheet (GNS) /Epoxy hybrid composites. There are three parts in this study. The first part of this research is the surface treatment of multi-walled carbon nanotubes (MWCNTs) by free radical reaction method, which is divided into two steps: 1. At first, the functionalized MWCNTs were prepared via free radical reaction with glycidylmethacrylate(GMA), which contains the epoxy group for polymerization on MWCNTs. 2. After GMA was polymerized on MWCNTs surface, Jeffamine® Jeffamine® Poly(oxyproplene)(POP-400) was grafted on GMA, which was assigned as GD400-MWCNTs. GD400-MWCNTs were analyzed by Raman spectrometer, X-ray photoelectron (XPS), Fourier transform infrared spectrometer (FT-IR) and thermogravimetric analysis (TGA). The morphology of GD400- MWCNTs were observed by Transmission electron microscope (TEM). The ID/IG area ratio of prinstine-MWCNTs and GD400-MWCNTs, are 1.08 and 1.16, respectively. The ID/IG values of GD400-MWCNTs indicate this modification will functionalize MWCNTs with slightly damage on the structure of MWCNTs. The characteristic absorption peaks of GD400-MWCNTs are more than that of prinstine-MWCNTs. There are characteristic peaks appeared, the peak at 285.60 eV corresponded to C-NH2, at 286.65 eV corresponded to C-O-C, on 286.86 eV corresponded to C-OH and at 288.00 eV corresponded to O-C=O, these peaks confirmed MWCNTs were successfully functionalized. The second part of this research is the redox reaction on Graphite Nano Sheet(GNS) that can reduce the number of layers of GNS, and increase their surface area to enhance the mechanical properties of composites. Modified GNS was analyzed by Raman spectrometer, X-ray photoelectron (XPS) and X-ray (XRD). The morphology of Modified GNS was observed by SEM and AFM. The Graphite Nano Sheet was exfoliated to form Graphene Oxide by using a modified Hummers method. The high density of oxygen functionalities on graphene oxide can provide chemical modified potentials and good dispersibility. XRD was used to observe the interlayer distance of graphite 002 plane, which indicated the that d-spacing of exfoliated Graphene Oxide changes from 3.4 Å to 7.3 Å. However, the Graphene Oxide possesses poor physical properties due to poor graphitic structure. In order to restore the graphitic structure of Graphene Oxide(GO), the chemical reduction had been used to reduce the Graphene Oxide(GO). The Raman and XPS were used to investigate the quality of graphitic structure and surface chemical composition of graphene-based materials. The results of Raman and XPS indicate that Graphene Sheet can be reduced effectively by chemical reduction. The FE-SEM was used to observe the surface morphology of GNS, GO and GS. The surfaces of GS exhibit typically crumpled and porous architectures which are different from carbon black and graphite. In this study, GNS, GO and GS were added into polymer matrix to investigate their effect on the mechanical properties of the polymer composites. The third part of this research is the preparation and characterization of the Pristine-MWCNTs/GNS/epoxy, GD400-MWCNTs/GNS/epoxy, GD400-MWCNTs/GO/epoxy and GD400-MWCNTs/GS/epoxy hybrid composites. From the tensile properties study, the following results were obtained: 1. When the Pristine-MWCNTs/GNS/Epoxy hybrid composites were prepared with 0.5 phr, 1.0 phr and 2.0 phr MWCNTs/GNS, it was found the best mechanical properties can be obtained with the lowest MWCNTs/GNS content (0.5 phr).Since the high nano filler content will cause aggregation and reduce its mechanical properties. 2. The hybrid composite of Pristine-MWCNTs/GNS with the ratio of 10/90 wt%(wt %) shows the best tensile modulus, tensile strength and elongation, which were 3361 MPa, 51 MPa and 2.9 %, respectively, and exhibit significant improvement comparing with neat epoxy (increase from 2646 MPa, 47.65 MPa and 2.6 %, the enhancement is 27.02 %, 6.93 % and 11.54 %, respectively.) Since adding carbon nanotubes can improve the dispersibility of GNS in epoxy matrix. 3. The tensile modulus, tensile strength and elongation of GD400- MWCNTs/GNS/Epoxy hybrid composite with MWCNTs/GNS ratio of 10/90 wt% were 3361 MPa, 61.52 MPa and 3.9 %, respectively (the enhancement is 27.04 %, 29.09% and 50% respectively, comparing with those of neat epoxy.) 4. The tensile modulus, tensile strength and elongation of GD400- MWCNTs/GO/Epoxy hybrid composite with MWCNTs/GO ratio of 10/90 wt% were 2940 MPa, 67.59 MPa, 4 %, respectively (the enhancement is 11.11%, 41.82% and 53.85% respectively, comparing with those of neat epoxy.) The tensile modulus, tensile strength and elongation of GD400-MWCNTs/ GS /Epoxy hybrid composite in MWCNTs/ GS 10/90 wt% were 3631 MPa, 9.32 MPa, 3.9 %, respectively (the enhancement is 37.22 %, 45.45 % and 50 % respectively, comparing with those of neat epoxy.) From the Glass Transition Temperature(Tg) study, the following results were obtained: 1. The hybrid composite of Pristine-MWCNTs/GNS with the ratio of 10/90 wt%(wt %) shows the highest Tg which was 52℃, respectively, and exhibit significant improvement comparing with neat epoxy (increase from 42.99 ℃, the enhancement is 20.96 %, respectively.) Since adding carbon nanotubes can improve the dispersibility of GNS in epoxy matrix. 2. The Tg of GD400- MWCNTs/GNS/Epoxy hybrid composite with MWCNTs/GNS ratio of 10/90 wt% was 52.69 ℃, respectively (the enhancement is 22.56%, comparing with those of neat epoxy.) 3. The Tg of GD400-MWCNTs/GO/Epoxy hybrid composite with MWCNTs/GO ratio of 10/90 wt% was 54.41 ℃, respectively (the enhancement is 26.56. %, respectively, comparing with those of neat epoxy.) The Tg of GD400-MWCNTs/GS/Epoxy hybrid composite in MWCNTs/ GS 10/90 wt% was 56.9℃, respectively (the enhancement is 32.36 %, respectively, comparing with those of neat epoxy.) From the Coefficient of thermal expansion (CTEα1 and CTEα2) study, the following results were obtained: 1. The hybrid composite of Pristine-MWCNTs/GNS with the ratio of 10/90 wt%(wt %) shows the lowest CTEα1 and CTEα2, which were 81 ppm/℃and 240 ppm/℃, respectively, and exhibit significant improvement comparing with neat epoxy (decrease from 90.2 ppm/℃ and 262.1 ppm/℃, the enhancement are 10.20 % and 8.43 %, respectively.) Since adding carbon nanotubes can improve the dispersibility of GNS in epoxy matrix. 2. The CTEα1 and CTEα2 of GD400-MWCNTs/GNS/Epoxy hybrid composite with MWCNTs/GNS ratio of 10/90 wt% were 80.22 ppm/℃ and 236.2 ppm/℃, respectively (the diminution are 11.06 % and 9.88 %, comparing with those of neat epoxy.) 3. The CTEα1 and CTEα2 of GD400-MWCNTs/GO/Epoxy hybrid composite with MWCNTs/GO ratio of 10/90 wt% were 79.36 ppm/℃ and 246.5 ppm/℃, respectively (the diminution are 12.02% and 5.95 %, comparing with those of neat epoxy.) The Tg of GD400-MWCNTs/GS/Epoxy hybrid composite in MWCNTs/GS 10/90 wt% were 70.13 ppm/℃ and 225.5 ppm/℃, respectively (he diminution are 22.25 % and 13.96 %, respectively, comparing with those of neat epoxy.) This study demonstrates a unique method to improve the mechanical properties of GNS, GO and GS filled epoxy composites via introducing one dimensional carbon nanotubes. Since long and tortuous MWCNTs can bridge the adjacent GNS, GO and GS and inhibit the face to face aggregation, resulting in a high contact area between 3-D hybrid architecture and polymer matrix. The tensile modulus, tensile strength and elongation of GD400-MWCNTs/ GS /Epoxy hybrid composite in MWCNTs/ GS 10/90 wt% were 3631 MPa, 9.32 MPa, 3.9 %, (the enhancement is 37.22 %, 45.45 %and 50 % respectively, comparing with those of neat epoxy.) Thus, minimizing the stacking effect and reducing aggregation of GNS, GO and GS are the most important issues to realize the potential of graphene-based composites.The 3-D hybrid architectures is a very important concept to improve reinforcing efficiency of graphene-base polymer composites.