Microwave-driven spheroidization for performance enhancement of ultra-fine powder coatings

Powder coatings are recognized for their eco-friendly properties but often result in thick films and less aesthetically pleasing finishes. In contrast, ultra-fine powder coatings offer the potential for thinner, smoother, and more attractive films while maintaining zero volatile organic compound (VOC) emissions. However, a predominant challenge associated with ultra-fine powders is their poor flowability. By achieving spherical particle shapes, flowability can be improved, highlighting the crucial role of particle shape in the powder industry. This study focuses on transforming the irregular shapes of powder coating particles into a more spherical form using microwave heating and nano silica particles (nano-SiO₂). The investigation includes an analysis of morphology, flow properties, and appearance characteristics, with variations in nano-SiO₂ content (0.5–1.75 wt%). The employed microwave provided rapid heating and caused only a negligible rise in molecular weight, implying no pre-curing. The microwave-driven method produced particles with an average sphericity (roundness, R) of 0.98. Meanwhile, the angle of repose (AOR) of the powder decreased by 17.8°, and the outflow rate increased from 6.9 g/min in the reference sample to 134.4 g/min, indicating a significant improvement in both static and dynamic flowability of the powder. The use of nano-SiO₂ combined with microwave heating offers a promising approach for spheroidizing irregular particles and enhancing the performance of ultra-fine powder coatings. As a result, the surface appearance of spherical specimens with an optimal amount of nano-SiO₂ improved significantly. However, excessive nano-SiO₂ content can counteract these benefits, suggesting that sphericity has a superior effect on the appearance of powder coatings when nano-SiO₂ levels are carefully optimized.