Assembling Lipoic Acid and Nanoclay into Nacre-Mimetic Nanocomposites

A facile strategy to obtain nacre-mimetic nanocomposite materials is presented. The proposed economically feasible and environmentally friendly process consists in fusing dynamic poly­(lipoic acid) and montmorillonite (MTM) via a water evaporation method. Lipoic acid (LA), a naturally occurring molecule, can readily undergo thermal-, UV-, or (water) evaporation-induced dynamic ring-opening polymerization. This monomer has been equipped with various organic and inorganic counter cations, altering the physical properties of both the obtained poly­(lipoate)­s and the resulting nacre-like nanocomposites. The mechanical performance of the nanocomposites can be accordingly tuned from rigid and brittle to soft and ductile. Importantly, the composites containing triethanolammonium cations show enhanced ductility with an elongation at break up to around 16% when compared to other reported nacre-mimetic nanocomposites with similar MTM content (elongation at break usually below 10%). Moreover, the influence of MTM content on the mechanical properties of the nanocomposites is elucidated. Furthermore, the dynamic nature of the poly­(lipoate)­s and supramolecular architecture within the composites enables water-assisted self-healing of superficial scratches, as evaluated by optical microscopy, and closed-loop recycling for materials with up to 70 wt % MTM. Finally, the nanocomposites were found to exhibit flame retardancy.