Size impact of microcapsules in room temperature, self-healing thermosets

Protective epoxy coatings for metal substrates are used for wear resistance and physical protection against environmental conditions that may result in physical or chemical changes, such as corrosion. Previous work done by Pratama et al. [1] investigated the use of encapsulated solutions containing maleimide-based healing agents for self-healing of furan functionalized epoxy networks through reversible Diels-Alder chemistry. Results from these studies show that the use of phenyl acetate (PA) as a solvent, and the concentration and structure of maleimide healing agent affects the degree of physical and chemical bonding across the crack surface. A urea-formaldehyde (UF) encapsulation technique was used to create capsules with a diameter of ≤ 300 μm and could recover 71% of its initial load after fracture. Such capsules are too large for incorporation into protective coatings that generally have a thickness of 30-40 μm. Thus, capsules with an approximate diameter of ≤ 20 μm were created by increasing shear rate and by incorporating ultrasonication processing to the UF encapsulation procedure. The purpose of this work is to study the relationship between capsule size and healing efficiency in self-healing thermosets.