Bio-inspired White Tablet Coating Film Without Titanium Dioxide

Titanium dioxide (TiO₂) is widely used as a white additive in food and pharmaceuticals, but its safety has raised increasing concerns. Currently, calcium carbonate is commonly used as an alternative to TiO₂ in white film coatings, although it provides inferior whiteness. With the development of the health industry, TiO₂-free and pigment-free white tablet coatings are becoming more desirable.

Inspired by white beetle scales, porous films were fabricated via phase separation between polyvinyl alcohol (PVA) and polyethylene glycol (PEG). The refractive index difference between polymer and air generated strong light scattering. Light-shielding effect of calcium carbonate of different morphologies was further investigated.

Under the same type of calcium carbonate as the opacifier, porous PVA/PEG films showed CIELab whiteness all above 80 (up to 87), much higher than the dense films using lipid plasticizers. With the same porous structure, quasi-rhombohedral calcium carbonate increased whiteness by 8.2% compared with spindle aggregates.

Porous structures dominated whiteness improvement. Bioinspired porous films via polymer-polymer phase separation represented a novel strategy for TiO₂-free white tablet coating, and could guide the screening of other phase-separating polymers to further improve the film whiteness and properties.