Modifying commercial water-based acrylic paint with Rice husk-derived silica aerogel fillers for building thermal insulation

Abstract

For building retrofitting and energy conservation, thermal insulation coatings provide a significant advantage over mineral wool due to their ease of spray application on complex 3D shapes. This study investigates the use of rice husk derived silica aerogel (SA) as a low-cost thermal insulation additive in commercial water-based acrylic paint. The highly porous SA with nanostructured closed pores significantly reduces thermal conductivity by effectively inhibiting heat transfer through the paint coating. The supercritically-dried SA was methyl-silanized to achieve a balance of hydrophobicity and maintain a high silanol density, enabling its compatibility within the water-based emulsion. The SA particles were directly added at 20, 40, and 60 vol% into the emulsion, followed by spray coating onto a bulk substrate resulted in a 1.3 ± 0.2 mm dry film thickness. The relationship between SA volume fraction on the paint properties was investigated through a comprehensive evaluation of aesthetic, mechanical, and thermal characteristics. The introduction of SA did not substantially alter the original paint color, although it increased surface roughness due to SA aggregation. These surface aggregates effectively impede heat transfer and contribute to the formation of a thermally insulating char layer during combustion. Concurrently, the combination of preserved SA porosity and surface hydrophobicity endowed the modified paint with low thermal conductivity (0.11–0.07 W/mK), high cohesive strength (1.3–2.7 MPa), and a high-water contact angle (θ° = 110°).