Chemically Functionalized Clay Epoxy Nanocomposites for Aerospace Applications
S. Balakrishnan, and D. Raghavan
Howard University, US
Keywords: Materials, Surfaces and Interfaces
Reinforcement of polymeric resin with nanoclay platelets has resulted in lightweight materials with enhanced mechanical and thermal properties. The selection of clay as reinforcing material is extremely appealing because of cost, high thermal inertness, and environmentally friendly characteristics. One of the major roadblocks in the wider use of nanoclay platelets in thermoset and thermoplastic polymeric materials has been the poor dispersion of polar clay into a non-polar polymer matrix. It is believed that consistent improvements in properties of clay loaded polymeric system can be achieved by minimizing clay aggregation, promoting the formation of chemical bonds between polymer and clay and achieving exfoliation of clay. The general expectation is that chemical coupling the functionalized clay sheets and the polymer can yield potential benefits of reinforcing nanofiller.
We report an approach to improve the compatability of clay and epoxy resin by ion-exchanging clay surface with functional surfactants. The reactive surfactants was synthesized from vernonia oil, an extract of renewable plant product. The oil was transesterified under basic medium and the intermediate was reduced using lithium aluminum hydride in hexane medium to obtain cis12, 13-epoxy-cis-9-nonadecenol (vernanol) as primary product. Vernanol was then converted into vernanyl mesylate, followed by reaction with potassium cyanide to obtain 13, 14-epoxy-cis-10-nonadecenitrile (C-19 nitrile). The C-19 nitrile was reduced with Lithium Aluminum Hydride in ether medium and then converted with HCl acid into 13 (14) Hydroxyl cis – 10-nonadecenyl amine hydrochloride (C-19 amine hydrochloride). The proton NMR of the reactive surfactant showed an intense singlet peak corresponding to a chemical shift at 8.2 d, characteristic of primary amine hydrochloride in the final compound (refer Fig. 1). The C13 NMR spectrum showed characteristic peaks for secondary alcohol groups at 62 d and 70 d, which suggests that the epoxy ring has opened during LAH reduction of nitrile compound. MALDI-TOF mass spectra for C-19 amine hydrochloride showed diagnostic peaks for M+ and M+1+ ions at m/z 298.5 and 299.5 amu respectively, which corresponds to primary ammonium cation.
The Na-Montmorillonite clay was ion-exchanged with reactive and non-reactive surfactant mixture (25:75 mole% of C-19 amine hydrochloride and octadecyl amine hydrochloride). The chemically functionalized clay and the epoxy resin were allowed to swell in a reactive diluent, glycidyl methacrylate (GMA). The mixture of swollen clay and epoxy resin was ultrasonicated, precured, and postcured to formulate epoxy nanocomposites. The nanocomposites were characterized using wide-angle x-ray diffraction and transmission electron microscopy. The absence of a peak at approximately 2.30 (2q) that corresponds to d001 reflection, indicates that the basal spacing has expanded and the nanoclay platelets may have partially exfoliated. To verify our results, we performed TEM of epoxy nanocomposites. At lower magnification (Figure 2a), we see considerable dispersion of clay platelets in epoxy matrix. At higher magnification (figure 2b), the micrograph shows partially exfoliated structure with some of the platelets randomly oriented, while others stacked with an interlayer separation of approximately 10nm. Studies are underway to quantify the degree of exfoliation and dispersion of clay platelets in epoxy nanocomposites and relate it to mechanical properties.
NSTI Nanotech 2003 Conference Technical Program Abstract