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Potato Starch Stars in New Coating Binder

Monday, January 15, 2018

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A newly developed coating formulation that uses potato starch as a key component is being touted by its creators as an eco-friendly, biobased option, and while it's viable mainly for indoor applications right now, research is underway to attempt to ready it for use in corrosion-protection coatings for steel substrates.

Researchers from Germany's Fraunhofer Institute for Manufacturing Engineering and Automation IPA, working in tandem with the Institution for Applied Polymer Research IAP, developed the coating; they say that previously, biobased binders or film formers were unable to meet important specifications for paint and varnish products.

This has changed with the use of modified starch.

Starch Solution

Traditionally, starch has been applied in the paper/corrugated cardboard and adhesives industries, noted Christina Gabriel, a scientist at the Fraunhofer IAP. But when it comes to paints and varnishes, starch was used only as an additive.

“With starch as the main component of a water-based dispersion, we now have very promising adhesion results,” Gabriel added.

© Photo Fraunhofer IAP

Researchers focused on developing a coating for metals used indoors, such as aluminum, which is often found in fire doors or window frames.

Researchers focused on developing a coating for metals used indoors, such as aluminum, which is often found in fire doors or window frames.

Development Challenges

Using starch as a main component for paints and varnishes still posed a challenge, however, as film formers have many roles to play, such as forming a continuous film, while also being compatible with additional layers and additives. There must also be the capacity to embed pigments and fillers.

"In its natural form, however, starch exhibits several properties, which stand in the way of its use as a film former,” Gabriel said.

“For example, it is not soluble in cold water and neither does it form continuous, non-brittle films. We therefore had to modify the starch to adapt it to the requirements, as in spite of all the challenges, as a renewable and cost-effective raw material, starch is of great interest for many sectors."

The solution? Breaking the starch down.

This process improves the material’s solubility in water and the solids content of the starch in water, as well as its film-forming ability, noted the Fraunhofer IAP.

This is not yet sufficient, however; while the film former should initially be soluble or dispersible in water, the coating must not dissolve. To address this, a chemical process known as esterification is employed, resulting in starch esters that are dispersible in water. These form continuous films that adhere well to substrates such as glass and aluminum.

The modified starch is then crosslinked, where the coating’s sensitivity to water to reduced further. Long-term stability tests expose the material to rapidly changing temperature cycles that replicate the change from day to night and the rotation of the seasons.

The material is also exposed to electrolyte-enriched water, in order to demonstrate how the coating reacts to water and how well it resists extreme conditions.

Current Testing

Testing is currently being conducted to determine the modified starch’s resistance to corrosion and adhesion to certain substrates.

"Apart from the already tested aluminum, two other important metals, steel and galvanized steel, are to be tested," said 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."

New recipes to increase coating optimization are also being tested.

   

Tagged categories: Asia Pacific; Coating Materials; Coating Materials; Coatings Technology; EMEA (Europe, Middle East and Africa); Latin America; North America; Renewable raw materials; Research and development; Z-Continents

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