Self-healing varnishes

The recent decade brought about new dimensions to materials developments; stimuliresponse materials capable of responding to internal or external stimuli. The ability of materials to autonomously self-heal is the most promising property [1]. The number of publications that appeared in the past decade concerning the self-repair of polymeric materials is quite extensive. They cover different fields of research, including thermoplastic and thermoset polymers, polymer composites, and coatings. The first ideas already started to develop in the 1990s, when scientists started to look at nature to solve the recurring problem of damage to materials [2]. The process of implementing a strategy of autorepair of a damage is a subject of increasing interest. One of the challenges for many of the already developed self- -repairing systems is to enhance the structural stability and mechanical properties of the materials. The first developed self-healing materials relied on microencapsulated healing agents within the bulk polymer [3]. Upon mechanical stress, the microcapsules were ruptured releasing agents that reacted with the catalyst in the polymer matrix to repair the damage [4–5]. Among many other crosslinking methods relying mainly on epoxy chemistry, ‘click’-based chemistry, the use of thiolene-based systems, as well as catalytic crosslinking reactions based on ring opening metathesis polymerization have found wide application in materials science. In the latter methodology, the catalyst present inside the matrix then promotes an autorepair reaction via ROMP. Thermosetting autorepair polymers which have been proposed so far include Grubbs’ first-generation catalyst; currently, the possibility of applying other ruthenium catalysts such as second-generation Grubbs’ catalyst and Hoveyda–Grubbs’ second-generation catalyst are under evaluation [3]. In addition to the aforementioned methods, you can also find self-healing coatings in the reaction of Diels-Alder. The self-healing concept envisages a similar recovery of material properties, such as fracture toughness, corrosion resistance, or conductivity, to improve the durability and reliability of the polymer materials. Damage due to impact, wear or fatigue initiates a healing mechanism that preferentially without external stimulus can recover any functionality. Researchers working in the field of self-healing polymeric materials mainly focus on high-end applications where the added value outweighs the cost of production. Such applications can, for example, be found in the transport sector, electronics, and structural materials. Car coatings, structural composites in airplanes, conductive polymers in sensors are only some examples of many targeted applications. Repair of damage in these materials is often laborious, not cost-efficient and only detected on the macroscopic level when it is too late. On the other hand, self -healing materials try to avoid macroscopic failure by responding immediately or at least fast enough to damage [1]