Mechanically induced dye-release from polyurea microcapsules in a rubbery adhesive

Especially in the building industry the demand for in situ monitoring concepts of adhesive joints persists. In a new approach, microcapsules filled with special dyes, are added into a rubbery adhesive. Certain stress levels within the adhesive lead to a breakage of the capsules, which release their liquid cores. This results in a detectable colour change and thus, enables non-destructive condition monitoring of the bond. Dye-filled polyurea microcapsules were produced by interfacial polymerization by varying synthesis parameters while their influence on capsule morphology and wall thickness was determined. The morphology and thermal properties of the microcapsules were characterized by scanning electron microscopy and dynamic differential calorimetry, respectively. Subsequently, the method of nanoindentation was used to study the deformation and fracture behaviour of the microcapsules. Finally, it was analysed to what extent the microcapsules break within a polymer matrix, e.g. by critical stress levels or deformations. This development is a new quality assurance method for glass façades.