Effect of confinement level and local heating on healing efficiency of self-healing particulate composites

Shape memory polymer based self-healing materials are a special class of materials that have been the subject of much research over the past decade and many impactful discoveries have been made thus far. In a previous study (Compos. Sci. Technol. 2010; 70: 1419–1427) it was shown that in order for efficient healing, confinement during healing is essential. It was also shown that use of a two-step close-then-heal (CTH) method during healing of damaged shape memory particulate composites provided molecular scale healing. The present study further investigates the influence of confinement levels and local heating on the healing efficiencies of a polystyrene based shape memory polymer with 6% by volume of thermoplastic particle additives (copolyester as solid healing agent). The healing process was conducted by locally heating fractured cylindrical specimens at three levels of lateral (radial) confinements and axial constraints, and varying heating times. It is found that, lateral confinement levels, axial constraints, and heating times all control the healing efficiency. Almost complete strength recovery is obtained with 100% lateral confinement, 12 MPa axial constraint stress, and 60 min of heating time.