Graphene derivatives as self-healing enhancers in functional polyurethane coatings

Embedding nanofillers within a matrix remains a well-studied approach to improve the properties of the neat polymers. In particular, the incorporation of graphene derivatives within polymers that exhibit self-healing capabilities could significantly enhance the self-healing performance by further promoting the reassembling of reversible bonds, thus, reinforcing the relevant intrinsic self-healing mechanisms. Motivated by the unique capabilities of graphene oxide (GO) to form hydrogen bonds and of reduced GO (rGO) as an ideal thermal conductor, we utilized partially reduced GO (p-rGO), synthesized by reducing GO under mild conditions, as an additive incorporated within a waterborne polycarbonate polyol-based polyurethane (PU) at various low concentrations between 0.015 wt% and 0.050 wt%. This significantly enhances the self-healing capacity of neat PU from ∼55% to ∼83%, when heated at 90 °C for 22 h; the self-healing behavior was quantified by grey value analysis of the damaged/restored area. The acceleration of the self-healing process in the case of p-rGO can be understood as being due to a synergy of two self-healing mechanisms that act complementary: the presence of residual oxygen functionalities on the p-rGO flakes favors the formation of hydrogen bonds between p-rGO and the functional groups of the PU, whereas the high thermal conductivity of p-rGO allows effective heat diffusion within the PU matrix, thus, increasing chain mobility. To our knowledge, it is the first time in the literature that p-rGO is used as a self-healing enhancer in PU-based coatings. As the need for the development of novel high-performance self-healing systems increases, the present study provides a new approach in the field of self-healing decorative coatings, in which the morphological restoration of the cracks is of particular importance, rather than the mechanical recovery, aiming to highlight the unique potential of graphene derivatives when embedded within a polymer, to be further integrated in everyday life applications.