In Germany alone, 100,000 tonnes of coating materials for protection against corrosion are produced every year. However, in the past, paints and varnishes with bio-based binders or film formers have usually been too expensive or could not meet the requirements.
Through the use of modified starch, scientists at the Fraunhofer IAP have found a way which even in this field makes sustainable and cost-effective solutions possible. ‘In the field of paints and varnishes, starch was usually only used as a additive’, says Christina Gabriel, a scientist at the Fraunhofer IAP in Potsdam-Golm. ‘With starch as the main component of a water-based dispersion, we now have very promising adhesion results.’ At the center of the research is the coating of metals for indoor use, for example aluminum, which can be used for fire doors, computer housings or window frames.
The solution by the Potsdam scientists involves the starch initially being broken down in order to improve its solubility in water and the subsequently associated solids content of the starch in water, as well as its film forming ability. After application however, the coating must no longer dissolve in water. The starch must therefore be modified further, by esterification. The resulting starch esters are dispersible in water, form continuous films and have very good adhesive properties on glass and aluminum surfaces.
The stability tests to check the long-term stability are then also carried out at the Fraunhofer IPA. In the next step, the resistance to corrosion and adhesion of the modified starch on different metal substrates is examined. New ‘recipes’ are also being tested, which are intended to optimize the properties of the coating even further.
‘Apart from the already tested aluminum, two other important metals, steel and galvanized steel, are to be tested’, states Gabriel. ‘Our investigations show that with its good film forming and very good adhesion properties on various materials, starch esters have the potential to be future alternatives to petroleum-based film formers in the coatings industry.’