Effect of aging on mechanical properties of resorcinol-formaldehyde gels

Resorcinol-Formaldehyde gels have been prepared in aqueous solutions. After a gelification stage at 80 degreesC, an aging was performed in water or acetic acid solutions at ambient temperature or in the parent liquid at 80 degreesC for different durations. Shear modulus of gels immersed in water is measured using the 3 points bending technique. The evolution of elastic constant with time depends on the pH of aging solution. The strengthening is more pronounced for aging under acidic conditions than in water. Nevertheless when the aging stage is performed at 80 degreesC for a few days, quite identical values of shear modulus are obtained comparatively to acid treatment. The enhancement of mechanical properties of RF gels in acidic conditions is related to polycondensation reaction rates.