Failure of elastic-plastic core-shell microcapsules under compression

Characterization of the failure behavior of microcapsules is extremely important to control the release of their core actives by mechanical forces. The strain and stress of elastic-plastic uninflated core-shell microcapsules at failure (rupture or bursting) has been determined using finite element modeling (FEM) and micromanipulation compression experiments. The ductile failure of polymeric microcapsules at high deformations is considered to occur when the maximum strain in the shell exceeds a critical strain, resulting in their rupture. FEM has been used to determine the maximum strains present in the capsule wall at different deformations for three types of shell material: elastic, elastic-perfectly plastic and elastic-perfectly plastic with strain hardening at large strains. The results obtained were used to determine the failure strain and stress of melamine-formaldehyde microcapsules, with average population values of ~0.48 and ~350 MPa, respectively. Thus, the elastic-plastic stress-strain relationship has been determined for the core-shell microcapsules tested.