Bio-inspired self-healing polymer foams with bilayered capsule systems

Bio-inspired, self-healing polymer foams containing novel calcium-alginate capsule system was developed for load-bearing application. The capsules were created by a multi-stage encapsulating process that can encapsulate two mutually reactive healing agents within single capsules. The capsules had a bilayered structure with the epoxy resin encapsulated within the inner layer and the hardener within the outer layer. To evaluate the mechanical self-healing performance, the following tests were conducted, i.e. (1) cyclic quasi-static compression tests for foams; (2) quasi-static three-point bending for foam core sandwich beams; and (3) high-speed soft impact for foam core sandwich beams. Cyclic quasi-static compression tests demonstrated (1) bilayered capsule systems had better multiple self-healing effect compared to the dual capsule system without external interventions; and (2) bilayered capsules could enhance the stiffness and strength of foams. For foam core sandwich beams, the bilayered capsules did not have a noticeable effect on the effective stiffness of the beams; however, it could provide a noticeable self–healing effect when the damage occurred. The images obtained from scanning electron microscope (SEM) and X-ray microcomputed tomography (μCT) suggest that the micro-cracks induced by the static and impact loading were either fully or partially healed by the released healing agents without external interventions.