Wetenschap - 20 januari 2016

Painting with mussel techniques

tekst:
Roelof Kleis

A paint on water basis that flows well? It could be possible, Wageningen chemistry research shows. Courtesy of the mussel.

Photo: Rijkswaterstaat

Professional painters use paint on water basis. Out of necessity, because paint on the basis of volatile solvents is too unhealthy. But it is not pleasant. Waterborne products do not flow as nicely as alkyd paint, as each DIYer can tell you. Companies such as Akzo Nobel have therefore been searching for ‘water paints’  that flows well. ‘But they have no idea how’, says polymer chemist Marleen Kamperman.

Akzo Nobel was thus interested in financing a nice piece of fundamental research of one of Kamperman’s pupils, PhD student Juan Yang. The starting point for her research is the mussel. That animal firmly attaches itself to surfaces under water. Firm enough to withstand heavy waves. The mussel does this with a string of protein polymer. The strings are secreted out of the foot in a liquid and aqueous form.

mosselproefschrift.jpg

Once exposed to the environment a reaction takes place in which the strings cure and become strong and tough. That trick that the mussel performs is a model to what a water soluble paint should do, Kamperman explains. ‘Particles that remain in solution as a protein and harden in air. That is exactly what you want from paint.’

The chemistry behind this was thus mimicked from the mussel: the polymerization of catechol with protein amine. This results in a polymer that is in fact a long chain where catechol are attached to it as charms. This catechol-amine polymer is water soluble in an acidic environment and cures in air. This curing is based on a rapid mutual oxidation of the catechol side groups of various chains. The resulting network forms a thin film.

The cure is initiated by lowering the acidity of the solution. This is also one of the problems that still needs to be overcome to be able to achieve a practically applicable paint, Kamperman explains. ‘The paint systems of Akzo Nobel are in fact based on increasing the acidity as the paint is applied. They are put off by a system in which the cure occurs in a alkaline environment. You have to change all the components of the paint, also the pigment for example, so that also they will remain stable in our route.’

Besides that other questions remain to be answered. How, for example, does the paint flow? ‘We have developed a water soluble system’, says Kamperman, ‘but we have not investigated how this system flows. Moreover, the polymer that we have developed is still too long, which is disadvantageous for the solubility. We must still learn how to steer that process.’ So there is still some work to be done before the first mussel paint can be found in the stores. Kamperman hopes that Akzo Nobel wants to continue with her group.


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