Thermodynamic characterization of separation phenomena at the silica/polymer interface within glass-reinforced composites using adsorption chromatography. Part I

Glass-reinforced thermoset epoxies do not exhibit their theoretical mechanical performance because the interface between the glass and the polymer is weak. It is well known that glass surfaces can separate compounds differing in polarity because the silica surface is acidic and highly polar. Adsorption chromatography on silica stationary phases can be used to quantitatively evaluate the thermodynamics of separation phenomena. A variety of surface modifications are commonly used to qualitatively enhance the bonding between silica and the organic matrix; however, this report provides baseline data on the interactions between unmodified silica surfaces and a resin-hardener pair typical of those used in commercial glass-reinforced polymer composites. The adsorption equilibria of the polyfunctional amine, Jeffamine T-403, and the bifunctional epoxide. DER332, were quantitatively compared on an unmodified silica liquid chromatography column. It was determined that the competition between these premix components for the silica surface was dominated by Jeffamine, with a value greater than 220 for the equilibrium constant, K, for this sorption process at room temperature. This constant was calculated from the chromatographic retention factors. k', determined for the monomers by measurement of their times of retention. tR, in a 15 cm column using eluents of differing polarity. The thermodynamic Gibbs energy for this process was determined from the equilibrium constant to be at least-13 kJ/mol.