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

Abstract

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, SiO2, Al2O3, and TiO2, 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 Al2O3-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.