Easily Recyclable White Polymer Films as Replacement for TiO₂ Pigments

Titanium dioxide (TiO₂) has developed in recent decades as a standard white pigment for paints, coatings, films, cosmetics, and foods. But it has repeatedly come under criticism for its potential hazard for the environment and health. Therefore, its use as a food additive has been banned in Europe and further restrictions are expected worldwide. Consequently, replacements are being intensively sought. We, therefore, present a bio-inspired polymer structure that is fabricated via foaming polymers with supercritical CO₂. In that way, tiny nanobubbles are formed inside the polymer, turning the originally transparent material perfectly white. This is a purely structural effect; all other material properties of the respective polymer stay unchanged. Therefore, the respective polymer remains a mono-fraction simplifying recycling dramatically. The process is environmental-friendly and can be utilized with bio-based polymers such as PLA (polylactide) or cellulose acetate and is highly scalable. The foamed films can be used directly and also tolerate further process steps, such as thermoforming.