Fracture resistance of epoxy-based composites with dopamine-modified nano-fillers

Abstract

In this work, polydopamine-coated MMT clay (D-clay) and polydopamine-coated carbon nano fibre (D-CNF) has been prepared via a novel slurry method. The modified D-clay and D-CNF are then incorporated into epoxy resin to form nanocomposites. The characterization of the D-clay epoxy nanocomposites was carried out using X-ray diffraction (XRD), transmission electron microscope (TEM), thermal gravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Young’s modulus and fracture toughness were determined by a mechanical tester. Young’s modulus increases with increasing D-clay and D-CNF loading. However, the fracture toughness decreases with increased D-clay loading but increases with increased D-CNF loading.

Explanation has been made with the aid of fractographic analysis using scanning electron microscope (SEM), as well as TEM observation of the crack-clay interactions. It was found that although polydopamine (PDOPA) provides a strong adhesion between the fillers and the matrix, leading to enhanced elastic stiffness, the enhancement prohibits energy release via secondary cracking, resulting in a decrease in fracture toughness. Comparative study with virgin clay (V-clay) nanocomposites shows increased fracture toughness, which supports our explanation for the decreased toughness in D-clay composites.

The comparison with D-CNF epoxy composites reveals the effect of the type and form factor of nanofillers on the mechanical properties of nanocomposites. Explanation has been made with the aid of fractographic analysis, as well as TEM observation of the crack-fibre interactions. Comparative study with modified CNF shows an increase in fracture toughness. The result indicates that the clay form factor does affect the fracture toughness of the nanocomposites.