Study on the Self-Repairing Effect of Nanoclay in Powder Coatings for Corrosion Protection

Abstract

Powder coatings are a promising, solvent-free alternative to traditional liquid coatings due to the superior corrosion protection they provide. This study investigates the effects of incorporating montmorillonite-based nanoclay additives with different particle sizes into polyester/triglycidyl isocyanurate (polyester/TGIC) powder coatings. The objective is to enhance the corrosion-protective function of the coatings while addressing the limitations of commonly employed epoxy-based coating systems that exhibit inferior UV resistance. The anti-corrosive and surface qualities of the coatings were evaluated via neutral salt spray tests, electrochemical measurements, and surface analytical techniques. Results show that the nanoclay with a larger particle size of 18.38 µm (D50, V) exhibits a better barrier effect at a lower dosage of 4%, while a high dosage leads to severe defects in the coating film. Interestingly, the coating capacitance is found, via electrochemical impedance spectroscopy, to decrease during the immersion test, indicating a self-repairing capability of the nanoclay, arising from its swelling and expansion. Neutral salt spray tests suggest an optimal nanoclay dosage of 2%, with the smaller particle size (8.64 µm, D50, V) nanoclay providing protection for 1.5 times as many salt spray hours as the nanoclay with a larger particle size. Overall, incorporating montmorillonite-based nanoclay additives is suggested to be a cost-effective approach for significantly enhancing the anti-corrosive function of powder coatings, expanding their application to outdoor environments.

Synergistic Effect of Nanoclay and Barium Sulfate Fillers on the Corrosion Resistance of Polyester Powder Coatings

“…Comparing these results with the R p values obtained for the optimal condition of C1 (4%) in the previous study (ranging between 10 9 and 10 8 Ω•cm 2 ) [7], it is evident that the current coatings, which include the BaSO 4 , provided a slightly lower level of long-term barrier protection. However, this drawback is offset by the significant reduction in cost (about 15%).…”

“…This can be attributed to the larger contact area o the coarser particles with the binder matrices. Additionally, the finer particles resulted i significantly more entrapped air packets on their surfaces, leading to aggravated electro lyte ingress [7]. Consequently, the coating with 4% nanoclay C1 exhibited the highest pe formance, as evidenced by its highest Rpore, aligning with the results from the OCP and R measurements.…”

“…Optimal dosages for each additive were determined through systematic incorporation into the coating binder, followed by evaluation using applicable ASTM standards, electrochemical measurements, and surface and structure characterization. The nanoclay with a larger particle size exhibited more superior barrier properties and self-repairing capabilities in the neutral salt spray and electrochemical tests than the smaller one [7].…”

“…During the immersion period, an increase in the constant phase element (CPE coat ) and the corresponding exponential factor α coat values of the coatings was observed for coatings C1-02%-PB and C2-02%-PB, indicating the self-repairing function of the nanoclay [7]. Additionally, a decrease in the charge transfer resistance (R ct ) value signified the delamination of the coating from the substrate [33,34], as shown in salt spray tests.…”

“…We have evaluated the performance of two commercially available montmorillonitebased nanoclays, Claytone ® HT (C1) and CLOISITE ® 30B (C2), as anti-corrosive additives in the polyester/triglycidyl isocyanurate (TGIC) clearcoat powder coating system [7]. Both clays have a layered structure and a high aspect ratio, which can increase the tortuosity of coating films, decrease the permeability, and slow down the electrolyte ingress when the coating is exposed to a corrosive environment [8,9].…”