Enhancement of the long-term storage stability of one-part epoxy systems through the microencapsulation of thermal latent accelerators

 
Thermosetting polymers, like epoxy resins, have a special importance as one-part formulations due to their simple handling and processability, in which dicyandiamide (DICY) is usually used as thermal latent hardener. Urons or imidazoles are employed as accelerators to increase the reactivity and reduce the curing temperature of these epoxy systems. However, these accelerators dramatically reduce the storage stability of the formulation (few days at room temperature). By means of spray drying, it was possible to microencapsulate a powdered urone accelerator in such a way that a significant increase in storage stability (over two months) of the epoxy formulation could be achieved. The investigations dealt with the material and process parameters of the spray drying process and the reactivity, vicosity and the storage stability of the epoxy resin system. Gum arabic, which is already established in the food and pharmaceutical industries, has been successfully tested as encapsulation material.