Synergies of Nanocopper and Graphene as Cofillers in a Shape-Memory Polyurethane

Graphene and its related materials are commonly used as reinforcements in shape-memory polymers (SMPs) to engineer their functional properties, but at the cost of a reduction in their failure strain. Here, we demonstrate that the reduced failure strain in multilayer graphene reinforced polyurethane (PU/MGR) composites (at 2.0 wt % MGR) could be enhanced by more than two times with the introduction of copper nanoparticle (CuNP) cofillers (0.1–1.0 wt % CuNP). The CuNPs play a crucial role in disrupting the π–π and van der Waals interactions between the MGR sheets, which serve to reduce their agglomeration and suppress the number of stress–concentration sites. Interestingly, introduction of CuNPs was found to not only increase the failure strain but also contribute to remarkable tribological and thermal properties of the PU/MGR/CuNP composites. CuNP-decorated MGR fillers present at a sliding tribo-interface enabled the easy shearing and rolling of MGR sheets across each other, thereby significantly reducing the friction to attain a state of superlubricity exhibiting an ultralow and stable coefficient of friction of ∼0.05–0.06. These concepts derived from using CuNPs as cofillers in graphene-reinforced PU may be extended to many other SMP systems for various functional systems.