Gelation kinetics in elastomer/thermoset polymer blends

Abstract

The chemical gelation of polymer blends involving a thermoset component has been investigated utilizing multiple waveform dynamic rheology, complemented by differential scanning calorimetry and small angle x-ray scattering measurements. Three epoxy/rubber mixtures, with different degrees of pre-reacted material and catalyst, were used. The curing temperatures were determined with simple temperature ramps, whereas the characteristic gel times were quantified using the well-known self-similarity of the gel structure, which yielded a very low gel exponent (0.05), indicative of the high molecular weights and additives used in the samples; this exponent was unchanged with temperature, suggesting the same gelation mechanism. These times decreased with increasing temperature. Gelation was not affecting the phase-separated morphology. The presence of pre-reacted material and catalyst were found to reduce the gel times (for different temperature steps). Finally, the shear history of the samples did not affet the curing temperatures and kinetics. These results can serve as a useful guide for appropriately blending thermosetting and thermoplastic compounds in order to obtain structural materials for different applications.