Epoxy/Layered Double Hydroxide Nanocomposites: Investigating the Influence of Preparation Method on Mechanical Properties

This study investigates the macro- and micromechanical properties of epoxy-based nanocomposites containing Mg-Al/NO3 layered double hydroxides (LDHs), with a comparative evaluation of two preparation routes: solvent exchange and direct drying from an aqueous LDH slurry. LDHs were characterised using atomic force microscopy (AFM), scanning transmission electron microscopy, and X-ray diffraction methods. Tensile tests and AFM nanomechanical mapping were used to obtain the macro- and micromechanical properties of LDH/epoxy nanocomposites, respectively. Both preparation methods resulted in nanocomposites with comparable mechanical performance. Young’s modulus increased by approximately 30–70% at lower LDH loadings (1–2 wt.%), and the ultimate tensile strength remained largely unchanged compared to pure epoxy. At higher LDH contents, tensile strength decreased by approximately 15–26%, while fracture strain decreased by up to 54%, which was attributed to particle aggregation, as confirmed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The mechanical response and stiffness maps obtained by the peak force AFM nanomechanical mapping revealed that nanocomposites prepared using solvent-exchanged LDHs exhibit significantly narrower interfacial widths and higher stiffness compared to those made by the conventional approach, indicating improved interfacial bonding and mechanical performance. Overall, the solvent-exchange approach proved effective for improving the interfacial properties and stiffness of epoxy/LDH nanocomposites.