The Effect of Adherends on the Curing of an Epoxy Adhesive

The effect of E-glass, cured vinyl ester resin, and silica gel on the curing of an epoxy-anhydride adhesive was examined. The techniques used were calorimetry in both isothermal and scanning modes and Fourier transform infrared spectroscopy in the attenuated total reflectance (ATR-FTIR) mode. Isothermal calorimetry was used to obtain the exotherm, conversion rate, and curing kinetic parameters, and scanning calorimetry was used to obtain the glass transition temperature. ATR-FTIR was used to study the curing kinetics and chemistry of the adhesive. The results suggest either the immobilization of a layer of the epoxy adhesive adjacent to inert solid surfaces or selective adsorption of the accelerator or both, each of which suppresses the cure reaction. This was reversed by the presence of adsorbed water. At least for this epoxy-anhydride system, adsorbed water seems to have had the beneficial effect of increasing the crosslink density in the interfacial region between the adhesive and adherend. Water seems also to change the overall cure reaction, causing more ether formation and less ester formation than without water. An additional finding was that the cured vinyl ester surface appeared to have a catalytic effect on the reaction, perhaps in conjunction with the accelerator, benzyldimethylamine.