Multi-level self-healing ability of shape memory polyurethane coating with microcapsules by induction heating

A shape-memory polyurethane (SMPU) was designed and used in the field of self-healing coating due to the capability to recover to its permanent shape in a predefined way. This technique could be modified by two different kinds of microcapsules to improve the localized corrosion resistance of healed coating by induction heating. For this purpose, the SMPU was synthesized by solvent polymerization using isophorone diisocyanate (IPDI) as hard segments and polycaprolactone (PCL) as soft segments. The results obtained from dynamic mechanical thermal analysis (DMTA) displayed a phase-separation structure, which is consistent with the results of 1H NMR characterization. The repeatable shape-memory measurements further demonstrated that the shape recovery of SMPU is above 75%. Appending some microcapsules embedding Alodine 5200 and a heat-generating agent into SMPU, adhesion of aluminum substrate with healed coatings could be greatly improved, as well as corrosion resistance. In addition, the heat released from the exothermic reaction between the heat-generating agent and oxygen are supplied to the shape-memory recovery of polyurethane. It was clear that the corrosion resistance evaluations (by electrochemical impedance spectroscopy and scanning Kelvin probe measurements) confirm that the modified shape memory polyurethane have comparable healing efficiencies (η = 77.3%) and excellent self-healing performances.