Unveiling the synergistic impact of nanoclay on the mechanical performance of polyester nanocomposite coatings

Abstract

Abstract

Polyester coatings on pre-coated metal (PCM), typically crosslinked with hexamethoxymethyl melamine (HMMM), must provide both wear resistance and high formability. However, increasing hardness to improve wear resistance often reduces toughness, compromising formability. Although nanoclay incorporation has emerged as a promising strategy to mitigate this trade-off, its interactions with the polyester-HMMM network remain poorly understood. This study systematically evaluates the synergistic effects of surface-modified Lucentite (LU) nanoclay and HMMM on hardness ( H ), creep resistance, formability, and wear performance. LU-HMMM interactions produced a complex, non-linear influence that departed from classic rule-of-mixtures predictions. Low LU loadings (≤0.5 wt%) increased H by 5–12% and reduced creep. At higher LU loadings (3–5 wt%), however, hydroxyl groups on the LU consumed HMMM, reducing crosslinking and lowering H by 23–26%. At 30–40 wt% HMMM, excess crosslinker limited hardness gains from low LU additions. At moderate LU loadings (0.25–1 wt%), toughness improved without compromising hardness, overcoming the conventional hardness-toughness trade-off as LU-induced softening remained minimal, allowing nanoclay reinforcement and crack suppression. The highest wear resistance was achieved by coatings containing 0.25 wt% LU with 30 wt% HMMM and 3 wt% LU with 40 wt% HMMM, owing to an optimal balance of hardness, toughness, and surface roughness.