The lotus plant's extraordinary ability to keep itself clean by means of the ultrafine surface structures on its leaves has led to Buddhism's holy flower becoming rather a celebrity in our latitudes, too. Yet we can also observe this self-cleaning effect on our own indigenous plants such as the nasturtium, reed or lady's mantle: water droplets just roll off the surface of their leaves, taking particles of dirt along with them.
Learning from nature's example, science has recognized that it is not the smoothest possible surfaces but those with structures measuring some dozens of nanometers that repel dirt and water most effectively.
About ten years ago, dirt repellent wall paints were the first marketed products to technically utilize this self-cleaning effect. With Mincor® TX TT, BASF is now starting a new chapter: this innovative finishing material endows technical textiles for awnings, sunshades, sails and tents with the same self-cleaning effect as the lotus. What on the surface of the plant leaves are tiny papillae, on treated textiles are innumerable particles with a diameter of less than 100 nanometers embedded in a carrier matrix. Whether nature or technology - the effect is the same: these tiny nubs keep water droplets and particles of dirt at bay.
This is why, on the lotus plant only two to three percent of the droplet surface is in contact with the plant leaf. Because this minimal contact is confined to the outermost tips of the papillae, the adhesive forces that would otherwise cause a droplet to spread are also minimal. Instead, the water's surface tension forces prevail and invariably cause the droplet to form a spherical globule - and the water just rolls off. Particles of dirt on the surface, which because of the papillae also have hardly any contact with the leaf surface or the fabric treated with Mincor® TX TT, are carried along by the droplets and washed away without any need for detergents or scrubbing.
The principle sounds simple, but its practical implementation on textiles with the aid of Mincor® TX TT was a challenge for BASF's nanotechnologists. The main objective was to optimize the processing and durability of the finishing. "The solution is a composite material consisting of nanoparticles firmly embedded in a carrier matrix", explains Dr. Ralf Nörenberg, Head of BASF's Competence Center for Technical Textiles. The resulting composite has the required nanostructured surface, but does not release any nanoparticles, as extensive tests have proved.
In 2006, polyester awning fabrics finished with Mincor® TX TT were very successful in achieving the transition from the laboratory to practical application, and fabrics for sunshades and sails treated with Mincor® TX TT are also now in the trial phase. "This type of finishing is an ideal solution for these kind of fabrics that are continuously exposed to the outdoor elements and can't be put in a washing machine", says Nörenberg. "The next shower of rain washes off the dirt, and in prolonged periods of dry weather all that's needed is a brief shower from the garden hose."
With its seal of quality: "Selfcleaning inspired by nature", the Denkendorf Institute of Textile and Process Engineering (ITV) has established a new market standard. Only textile products proved to have a genuine self-cleaning effect based on nanostructured surfaces - like its model in nature - can receive this quality seal. "The first products that meet these strict standards and have been granted the quality seal are polyester fabrics finished with Mincor® TX TT", explains ITV's Dr. Thomas Stegmaier. Words like "nano" are now being lavished on countless products as promotional tags to boost their market potential. "But these products don't always deliver what they claim: at most one third of them", estimates Stegmaier, "meet accepted definitions of nanotechnology as used for example by the German Ministry of Education and Research (BMBF). We have therefore devised this quality seal as a form of guidance for consumers, at least where textiles are concerned."
Source: BASF, take a look an animation