Polymer nanocomposite adhesives with internal nano-heaters to facilitate multilayer laminate separation

Laminating adhesives used in multilayer films present strong, irreversible adhesion that limits the produced packaging systems to single-use applications. From a sustainability point of view, the recovery of individual polymers after use is imperative and a pivotal step is to make this adhesion reversible via breakdown of the adhesive structure. This work describes a promising strategy based on the incorporation of graphene into thermoreversible adhesive resin formulations to trigger the rupture of the adhesive network by exposure to IR radiation. Graphene is a thermal absorber that abruptly heats up under irradiation and efficiently dissipates this heat to the surrounding environment causing the adhesive network to collapse, resulting in remarkable changes in its mechanical properties. In this study, graphene was incorporated at low concentrations (0.25–1 wt %) into solvent-free polyurethane adhesives containing thermoreversible moieties. The photothermal effect at different loadings was evaluated and the formulation displaying the best balance between photothermal effect and optical properties was selected. Furthermore, the effect of irradiation on cyclability, fluidity and mechanical properties of the graphene-containing adhesives is evaluated. Good cyclability was observed and samples with a graphene loading of 0.25 wt % and 11.5 wt % of thermoreversible bonds (TRB) showed the largest difference in elongation under IR irradiation with respect to the neat adhesive. Creep testing demonstrated that the strain of this sample increases by almost 200% after irradiation due to the breakdown of the three-dimensional adhesive network triggered by the photothermal effect of graphene.