Incorporation of carbon nanotubes in epoxy polymer composites

Abstract

The goal of this research was to develop and explore methods for incorporating Single-Walled Carbon Nanotubes (SWNTs) into polymer matrices, to form composites, in which the presence of SWNTs would improve significantly their mechanical properties, electrical conductivity, and thermal conductivity. We have used the concept of interpenetrating polymer networks (IPNs) for the design of our composites. One (preformed) network would consist of tangled SWNTs. It would be penetrated and swollen by the prepolymer molecules, which would polymerize in place, forming the second (interpenetrating) network. For the polymer matrix we chose epoxy resin systems, because of their chemical versatility, low setting stresses, and good mechanical properties. The main problem to be overcome was the very pronounced tendency of SWNTs to aggregate and the inability of polymerizable organic molecules to penetrate the aggregates and disperse the SWNTs. Several attempts to disperse SWNTs into an epoxy-acrylate system, specially formulated for low viscosity, using sonication energy were not successful. Neither were attempts to infuse epoxy prepolymer into the pores of bucky paper. A novel process was developed, which uses solvent in conjunction with sonication to disperse SWNTs into epoxy prepolymers, then divides the system into droplets that are sprayed into a heated chamber and deposited on a heated substrate. Control of the relative rates of solvent evaporation and polymerization/cure resulted in the formation of composites with dispersed SWNTs. Such composites, containing 1 wt. % SWNTs showed a drop in electrical resistivity of ca. 14 orders of magnitude (5.0 Ohm•m, compared to 2.0 x 1014 Ohm•m for pure epoxy). An efficient method for making SWNTs/epoxy/fiberglass composites was developed by incorporating SWNTs on the surface of fiberglass using the incipient wetting method. Small amount of SWNTs (0.1 wt. % of SWNTs) increased the flexural strength of the composites by 13%. This method can be extended to other fiber reinforcements such as Kevlar, carbon fiber, and ceramic fibers. SWNTs were chemically bridged both glass fiber and Epoxy matrix in the glass fiber/SWNTs/Epoxy composites. Fluorinated SWNTs (F-SWNTs) were chemically reacted with amine group active silane agent coated glass fiber. Chemically coated SWNTs-glass fiber was further reacted with Epoxy matrix. Surface analysis of chemically coated SWNTs/glass fiber confirmed the introduction of chemical bonding between glass fiber and F-SWNTs. (Abstract shortened by UMI.)