Polymer alternative to white pigments
Polymer foils that are extremely thin and characterised by a high light scattering rate are being produced in a biomimetic process developed at Karlsruhe Institute of Technology (KIT) in Germany. Researchers claim that the material can be applied industrially to give objects an attractive white appearance and make them environmentally more compatible.
The team at KIT explains how titanium dioxide has been the standard pigment used for white colouring of lacquers, paints and plastics, as well as of cosmetics, foods, chewing gum, or pills. ‘Titanium dioxide has a very high refractive index - it reflects incident light almost completely. But it is associated with the drawback that its particles do not degrade and thus pollute the environment in the long term,’ says Professor Hendrik Hölscher of KIT’s Institute of Microstructure Technology (IMT).
He and his team were inspired by the white beetle Cyphochilus insulanus, whose chitin scales appear white thanks to their special nanostructure. ‘Based on this model, we produce polymer-based, solid, porous nanostructures, which resemble a sponge,’ says Hölscher, who heads the Biomimetic Surfaces Group of IMT. Similar to the bubbles of shaving or bathing foam, the structure scatters light, which makes the material appear white. At a thickness of 9µm, the polymer foil reflects more than 57% of the incident light, which rises to 80 to 90% if the thickness is increased.
‘Apart from foils, entire objects may be coloured white. As a next step, we plan to produce particles, e.g. small beads that are added to other materials,’ Hölscher adds.