Two Fraunhofer institutes have joined forces to tackle corrosion with a new form of metal coating based on renewable raw materials like potato starch.
Researchers at the Fraunhofer Institute for Applied Polymer Research IAP, in cooperation with the Fraunhofer Institute for Manufacturing Engineering and Automation IPA, hope their solution could someday do away with petroleum-based film formers.
Germany produces no less than 100,000 tons of coating materials for protection against corrosion every year – with a sizable majority of them being byproducts of petroleum. Paints and varnishes with bio-based binders or film formers are usually too expensive or fail to meet the industry’s requirements.
Now scientists at Fraunhofer IAP have found a way to make use of modified starch in making this field more sustainable and cost-effective.
Nevertheless, according to Fraunhofer IAP scientist Christina Gabriel, starch exhibits several properties, which stand in the way of its use as a film former. For example, it is not soluble in cold water and neither does it form continuous, non-brittle films.
The solution by the scientists involves an initial degradation step of the starch 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.
However, in order to produce a starch-based coating material, which is comparable with a conventional coating, this is not yet sufficient, as although the film former should initially be soluble or dispersible in water, the coating must subsequently no longer dissolve in water.
The starch must therefore be modified further. This takes place by way of a chemical process known as 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 tests, the coated materials are exposed to rapidly changing temperature cycles in a time-compressed form to simulate the change from day to night and the course of the seasons.
In addition, the test objects are exposed to electrolyte-enriched water in order to see how the coating reacts to water and how resistant it is under extreme conditions.
Image and content: Fraunhofer IAP