Brilliant white without pigments
A new process developed at the Karlsruhe Institute of Technology (KIT) has resulted in polymer films that are extremely thin and exhibit high light scattering. The cost-effective material can be applied industrially to a wide variety of objects to give them an attractive white appearance. The process can also make products more environmentally friendly.
A bright white surface gives furniture and other objects a clean, bright and modern appearance. Up to now, titanium dioxide has been the standard pigment for coloring paints, coatings and plastics, but also cosmetics, food, chewing gum or tablets white. However, the pigment is under criticism. "Titanium dioxide has a very high refractive index, it reflects incident light almost completely, but has the disadvantage that its particles do not degrade and thus pollute the environment in the long run," says Professor Hendrik Hölscher from the Institute of Microstructure Technology (IMT) of the KIT. In addition, there are concerns that titanium dioxide might potentially be harmful to health.
"We avoid the use of pigments that are harmful to the environment and health by creating porous polymer structures with a comparably high dispersion," says Hölscher. He and his team were inspired by the white beetle Cyphochilus insulanus, whose scales appear white thanks to a special nanostructure of its chitinous carapace. "Based on this model, we use polymers to produce solid, porous nanostructures that resemble a sponge," says Hölscher, who heads the Biomimetic Surfaces research group at IMT. Just like the bubbles of shaving or bath foam, the structure scatters the light, making the material appear white. The new technology for a cost-effective and harmless white appearance is suitable for a wide range of surfaces.
Environmentally friendly materials - modelled after nature
"The polymer films produced with our process are extremely thin, flexible and light, but still mechanically stable and can be applied industrially to a variety of products," the physicist explains. At a thickness of nine micrometers - nine thousandths of a millimeter - the newly developed polymer film reflects more than 57 percent of incident light. 80 to 90 percent can be achieved with a thicker film. For the development, the sponge-shaped microstructure was applied to acrylic glass. However, the process can be transferred to many other polymers. "In addition to films, entire objects can also be colored white. As a next step, we plan to produce particles, for example small beads, so that they can be incorporated into other materials," says Hölscher. "There are already inquiries from companies that are striving to make their products more environmentally friendly."
While engineers often developed solutions using materials consisting of many different chemical elements, nature usually limits itself to a single basic material that exhibits interesting mechanical, optical or physicochemical properties thanks to a complex three-dimensional structure. Bionics, which is concerned with understanding and imitating the phenomena of nature in order to make them technically usable, often leads to completely new solutions - which might never have been found in any other way, the researcher says.