Multifunctionality of supramolecular self-healing aeronautical nanocomposites

All materials are sensitive to damages. In the case of structural polymers, this usually makes the material unusable. The real challenge in the field of composite materials, suitably designed for structural applications (aircrafts, ships, wind turbine blades, automotive, etc.), consists in achieving specific targets such as: 1) weight reduction - to maximize the performance; 2) control of pollution during the manufacturing process of the materials and their use in service; 3) low consumption of fuel and resources; 4) reduction of the manufacturing and operating costs. Various criticalities, such as the absence of electrical and thermal conductivities and the poor impact damage resistance, severely limit the use of thermosetting resins for aeronautical applications, thus compromising their structural stability over time. An important step forward to contribute to the spread of use of structural composites can be reached by designing smart materials having autonomous damage-repair functionality and other specific functions integrated in the material structures. Commonly, self-healing polymeric materials can be divided into two different groups based on the approach chosen to impart self-healing functionality to the polymer. Based on this classification intrinsic or extrinsic systems can be developed. Extrinsic systems are often based on the microencapsulation concept. Recent extrinsic systems involve the use of a ruthenium initiator for Ring-Opening Metathesis Polymerization (ROMP), characterized by high thermal and chemical stability, able to preserve its own catalytic action in a very reactive. A very promising way to develop an intrinsic healing system is based on the supramolecular chemistry, which has a great influence on the overall mechanical properties of the final material. Usually, the supramolecular systems are characterized by repeatable and autonomous self-healing capability, but they have been developed for applications where no high mechanical performance of load-bearing materials is required. Supramolecular self-healing systems include dynamic covalent bonds and non-covalent interactions. In order to develop structural composites, which guarantee high mechanical performance and multifunctional properties, hybrid materials or nanomaterials have been functionalized with hydrogen bonding moieties able to activate supramolecular self-healing mechanisms and introduce additional functionalities. This work proposes an interesting strategy based on supramolecular chemistry with the aim of creating self-healing multifunctional materials for structural application in aeronautics and other fields, where high mechanical performance is required. In particular, the authors propose the use of molecules employed as self-healing fillers, having functional groups able to act both as hydrogen bonding donors and acceptors, to add into a toughened epoxy resin in combination with pristine Multiwall Carbon Nanotubes (MWCNTs) aimed at activating self-healing mechanisms and simultaneously conferring electrical conductivity to the resulting nanocomposites.