Paint and Coatings Industry News

Main News Page

The Self-Cleaning Coating? Research Suggests Hype May Hold Water

Friday, July 6, 2012

More items for Coatings Technology

Can lawn furniture, cell phones and even building façades clean themselves? The evidence suggests that the power of titanium dioxide to facilitate “self-cleaning coatings” is not some titanic fabrication.

Scientists at the Fraunhofer Institute Interfacial Engineering and Biotechnology (IGB) in Stuttgart, Germany, say testing there indicates the self-cleaning capabilities of TiO2 are indeed not so much baloney.

Or, dare we say, braunschweiger?

© Fraunhofer IGB

The surface coated with titanium dioxide molecules (right) looks very different from the non-coated sample (left).

In simple terms, the science behind TiO2’s self-cleaning claims holds that when sunlight hits the coated surface, the ultraviolet rays act as a catalyst, triggering an electrochemical reaction which produces free radicals, the Institute reported in an announcement on the technology. See: Cleaning with Sunlight.

“These and other active molecules strike a fatal blow to bacteria, fungi and similar organisms, first destroying the cell walls and then penetrating the cytoplasm—the substance that fills the cell—and damaging the bacteria’s DNA. As a result, the organic substances are destroyed instead of remaining stuck on the surface,” the scientists said.

The scientists investigated just how well these photocatalytic coatings work, including what organic elements they destroy and what they are powerless against.

The process used none other than a common mold haven—a garden chair.

“We ran some outdoor tests on garden chair armrests with photocatalytic coatings and compared them to ones made from conventional plastic,” said Dr. Iris Trick, group manager at the Fraunhofer IGB.

The team found that the formula “works on 30 different kinds of bacteria and fungi” after two years of testing.

Thinking Beyond Furniture

The scientists have tested the coating on glass and found that fingerprint smudges disappear after an hour of sun exposure.

“If you apply a thin coating of titanium dioxide to a glass surface such as a smartphone screen, the skin oils and fingerprints gradually disappear from the display by themselves,” says Dr. Michael Vergöhl, department head at the Fraunhofer Institute for Surface Engineering and Thin Films (IST) in Braunschweig and head of the Fraunhofer Photocatalysis Alliance.

“All that is needed is one hour of sunlight—unlike previous photocatalytic surfaces, which would have required the smartphone to be left in the sun for three days.”

The next step is to develop new materials that can also be activated by artificial light, the institute’s report says.

More information: Fraunhofer website.

The work of the German research team may be of note to those with an interest in this type of technology and use for TiO2. D+D has reported on a number of developments related to the technology, including self-cleaning exterior wall panels.

Technical experts from Alcoa Architectural Products gave D+D an exclusive look at its “self-cleaning” metal panels, which make use of the photocatalytic activity in TiO2 but do so while ensuring that same photocatalysis does not adversely affect organic paint and coatings on the surface. See: Why it Works: Alcoa Reviews Fundamentals of ‘Self-Cleaning’ Finish.

D+D also reported on an urban public-art, urban initiative in Manila, The Phillippines, that makes use of Boysen’s KNOxOUT paint. The product, according to product literature, “contains CristalActiv photocatalytic technology—ultrafine TiO2 that absorbs energy from light and transforms ordinary water vapor into hydroxyl and peroxyl radicals at the surface” thereby neutralizing smog. See: Painting a Brighter Airspace: Urban Art’s Public-Service Mission.