Crosslinking of epoxy resins at interfaces. IV. Anhydride‐cured resins at carbon and graphite surfaces

Abstract

AbstractDispersions of carbon blacks and chopped carbon fibers in epoxy resins may be characterized by infrared internal reflection spectroscopy (IR–IRS). The high surface areas of the carbons (often ≥ 100 m2/g) ensure a high degree of interfacial contact between the carbon surface and the polymer. The crosslinking kinetics and final crosslinked state of an anhydride‐cured epoxy resin are shown to be affected strongly by the carbons through adsorption of the tertiary amine catalyst at oxidation sites on the carbon surface. Oxidative treatments of the carbons (nitric acid oxidation, air oxidation) increase the effect on the crosslinking chemistry. Carbon dioxide treatment of the carbons, which produces a basic surface, reduces the effect on the crosslinking. The effects on the crosslinking kinetics were confirmed by differential scanning calorimetry (DSC). The relevance of these results to the characterization of the interphase in carbon fiber/epoxy composites is discussed.