Processing of kaolin micro-composite functional fillers for enhancing the near-IR reflective performance of polyurethane resin coatings

Polyurethane (PU) resin products meant for protective coatings are chemically composed of two-phase microstructures; soft ‘polyols’ and hard ‘diisocyanates and chain extenders’. For durable high-performance specialty PU coatings, their surface heat reflectance property is to be enhanced; otherwise, the absorption of solar heat energy eventually generates heat build-up that finally induces microstructural changes and chemical degradation. Hence, in this work, an attempt is made to improve the poor IR reflectance property of PU resin by incorporating kaolin micro-composite functional fillers. In this study, kaolin delamination was first carried out using alumina and zirconia milling media. Delaminated kaolin was treated with colloidal oxides, SiO ₂, Al ₂O _3, and TiO _2, to produce kaolin micro-composite fillers. The filler effect, chemical interaction, heat build-up, scratch resistance, and hydrophobic properties were examined, and results were presented. The study confirmed that when Al ₂O ₃-modified kaolin micro-composites improved the scratch resistance, the incorporation of 10 mass% mixed oxide kaolin micro-composite fillers enhanced the NIR reflecting property of PU coats from 4% to 53%. A facile strategy to enhance the solar heat shielding property of PU top coats for obtaining long-life durable protective coatings is presented in this work.