Working the classics
The Coatings Science International (Cosi) Conference 2019 came home to Nordwijk in the Netherlands to hold its annual meeting again almost directly at the beach. Around 90 international experts from 19 countries attended the event to learn about latest developments in the scientific coatings’ community.
This year some trends clearly stood out from the rest of the four-day programme. After numerous lectures about modern topics like functionalities or bio-based coatings, the conference focused more on some classic issues. Especially corrosion was a very dominant topic this year. And even though it has been explored since the beginning of natural sciences, the conference showed that there is still a lot to learn about corrosion and room for improvement regarding anti-corrosive coatings.
Alternative corrosion inhibitors
One example is the issue of the fairly toxic corrosion inhibitor chromate VI that needs to be replaced. Ander Cervella-Dominguez from the University of Manchester gave some new insights into the leaching behaviour of lithium salts, which could be used as an alternative. Especially lithium carbonate has a more or less similar leaching behaviour to strontium chromate. However, the salt alone is not the only factor that affects leaching. In his talk Cervella-Dominguez provided insights into the effect of the pigment volume concentration (PVC) on leaching.
Generally speaking, he showed that a high PVC increases the leaching, but that also the binder has an influence, which has to be accounted for. The target of all this work is to tune the coating in such a way that leaching of the lithium occurs fast enough to provide enough inhibitor to the substrate to counter corrosion. On the other hand, this should not occur too fast as it could lead to blistering in that case and the inhibitor could also run out too fast.
Later, in a second talk, his colleague Eugenio Bonetti, also from the University of Manchester, presented first results of a theoretical modelling that can describe the effect of PVC on the leaching mechanism with good fits to the experimental data.
Matthew Unthank of Northumbria University received the innovation award for his work on new epoxy hybrids.
Everybody working in the field of corrosion protection comes into contact with epoxy coatings. They are also very common for the protection of tanks or pipelines that are used to transport chemicals. In his lecture, Matthew Unthank of Northumbria University showed that by using trialkylborates it is possible to create new epoxy-amine-borate hybrid coatings with very promising barrier properties when compared to non-hybrid epoxies. He showed that the hybrid coating has a significant reduction of solvent uptake. Even for methanol the uptake was reduced by about 26 %, which normally is very hard to achieve. The lecture left some impression on the Cosi-committee and was later awarded with the Cosi Innovation Award.
Watching paint cure
Another prominent topic at Cosi 2019 was grazing incidence small-angle X-ray scattering GISAXS technology. The technique was presented to the coatings community for the first time by Stephan Roth from DESY Hamburg and KTH Stockholm two years ago at Cosi 2017. Since then it has been used more extensively. The technology is useful to investigate the nanostructure formation during deposition and subsequent drying of paints and inks.
The technology was applied in the research of multiple presenters. One example was a study of latex film formation where it showed a strong difference in the structure of the formed films between hard latexes with a Tg of over 50 °C and soft latex with a Tg below room temperature. In other lectures low angle x-ray scattering was presented as a technique to follow the development of nanostructures during in-situ photopolymerisation in thermosets or to explore the behaviour of silver nanowires in conductive and flexible composites.
Worth mentioning is also the presentation of Ingo Alig from Fraunhofer LBF (picture above). He presented his findings on the interplay of oxygen inhibition and inhibition by radical scavengers during curing free-radical polymerisation and cross linking of methacrylate resins. This is especially relevant for reactive coatings and other resins where one would like to control the duration of the inhibition period and to reduce the thickness of the oxygen inhibited unreacted surface layer. He showed that diffusion-controlled polymerisation leads to a sharpening of the interface between polymerised and unreacted region and to a reduced final conversion. For the development of the simulated model that showed good agreement with experimental data he was awarded with the Cosi Award for the most important scientific contribution.
New applications
Even though the conference has an academic focus, some new applications always pop up. This year’s most surprising one was a coating developed by Akzo Nobel that prevents insects from walking on walls. In her presentation Aurélie Féat showed how to choose the right binder and pigments to turn architectural coatings into slippery coatings that can prevent ants and other insects to get a good grip on the surface. She demonstrated that controlling the diameter of paint pigment particles and the particle size of the binder could strongly decrease adhesion of insects to the surface.
The presentation showed that by using the right PVC, solid particles at the top surface often detached and adhered to the tacky pads of insects. The coating itself, however, is not market-ready yet. Especially the weathering stability has to be increased before it could be used in real-world applications.
Jan Gesthuizen
