Dispersion of Silica Aerogel Particles in Thermal Insulating Waterborne Coating

Nowadays, thermal insulation coatings have attracted considerable attention as they are one of the most practical solutions to reduce energy consumption, by which greenhouse gas emissions are reduced. To prepare this composite, water-borne acrylic resin containing nano porous structures i.e. silica aerogel with two different particle sizes were considered. Firstly, the dispersion of the nano porous particles in water-borne acrylic resin was investigated. The main challenge was wetting and dispersing of aerogel particles in the waterborne resin, without any penetration of the dispersion medium in the nano pores. Three types of dispersant were used, and the dispersing process efficiency was characterized by a particle size analyzing, rheological behavior, zeta potential, and electron microscopy. The experimental results indicated that an anionic surfactant (sulfosuccinate) was more efficient than non-ionic surfactants (alkyl EO/PO copolymer and octylphenol ethoxylate). Additionally, the sufficient method to disperse the particles in water, and acrylic resin was studied. Owing to the consequences of the final particle size, the rheological behavior of the dispersion, and the diffusion of the medium into the nano pores, mechanical mixing with a mild shear rate and short mixing time was adopted. The thermal conductivity of the prepared coatings containing 2, 4, and 6 wt. % of aerogel particles was measured. The effect of concentration and size of aerogel particles on the thermal conductivity of acrylic film was evident. The results showed that it was possible to reduce 37-46 % of thermal conductivity using 6 wt. % of silica porous aerogels in the coating. Finally, the thermal transmittance (u-value) of a typical wall with the optimum insulating coating was calculated according to ISO 9869 standard. The results showed that the u-value would decrease by 24 % if the optimum coating was used with a thickness of 1.5 mm.