Hollow polymer-silica particles as an alternative to TiO2 opacifiers

The significant environmental impact associated with TiO₂ production has prompted the exploration of more sustainable alternatives for opacifiers. Polymeric hollow particles (HPs) emerged as promising candidates, but they have not yet been able to fully replace TiO₂ in coatings. In this study, we report for the first time a total replacement of TiO 2 using polymer-silica HPs, achieving comparable or superior optical properties. We investigate 3-(trimethoxysilyl)propyl methacrylate (TPM) HPs with different size and shell thickness in coatings formed under different environmental conditions in the presence of polymeric binder particles. The smaller HPs (1 μm diameter, 0.2 μm shell thickness) demonstrated superior optical properties, achieving solar reflectance values up to 73.3 % across the visible and near infrared spectrum. They outperformed both larger HPs (∼5 μm diameter, 0.25 μm shell thickness) and TiO₂ reference coatings containing the same mass percentage of opacifier. We report various film microstructures depending on the film forming conditions and correlate them with the interplay between diffusion, evaporation, and sedimentation processes. Importantly, high optical performance was maintained across the range of microstructures found, indicating reduced sensitivity to HP distribution within the coating. This is a promising feature when it comes to reliability of use in a range of industrial formulations. • Hollow polymer-silica particles were synthesized and tested as coating opacifiers. • Characterised particle distribution in coatings and linked it to theory. • Particle size and shell thickness strongly influenced optical performance. • Hollow particle coatings outperformed TiO₂ reference coatings. • Robust performance in 3 environments supports commercial use of hollow particles.