Chi Him Lo - Waterborne coatings for corrosion protection
Presentation - pdf
Chi Him Lo2, Bob Luigjes2, Simon R. Gibbon3, Stuart B. Lyon1, Lee A. Fielding1
1School of Materials, The University of Manchester, Manchester, M13 9PL, UK.
2AkzoNobel, Rijksstraatweg 31, 2171 AJ Sassenheim, The Netherlands.
3AkzoNobel, Stoneygate Lane, Felling, Gateshead, Tyne & Wear, NE10 0JY , UK
Surfactant additives are essential in waterborne direct-to-metal (DTM) formulations for attainment of coherent and defect-free films. However, residual surfactants are suspected of influencing film microstructure and can have adverse effects on the final coating properties (e.g. appearance, adhesion, viscoelasticity and/or barrier properties) [1,2]. In this work, atomic force microscopy infrared (AFM-IR) and scanning electron microscopy (SEM) are used to elucidate the additive-induced microstructural changes of polymer films and study the coating deterioration mechanisms after exposure to corrosive environments.
The results demonstrated AFM-IR can identify and map the sulfonate groups of anionic surfactants across the styrene-acrylic copolymer film. It has been found that varying the type or/and amount of sulfur-containing surfactant in the coating can cause significant differences in corrosion protection performance.
These findings can provide deeper insight into the relationships between binder-additive structures, film morphologies and the corrosion protection performance of formulated waterborne acrylic coatings.
Q&A
From Jordan Petkov : Do latex particles undergo coalescence the way emulsion droplets do? After all they have been polymerised prior ending up on the substrate? Isn't their deformability more important?
Answer: I would say that definitely, but also one thing we wanted to study in this project was how to adding a surfactant will affect the coating.
From Jordan Petkov : What is the hypothesis why the higher Tg results in larger three phase contact angle?
Answer: In this case is due to the increase in styrene content, we just change the monomer composition.
From Emma Michailidou : What is the effect of Tg on adhesion and corrosion protection you observe system specific or would you expect similar results with other types of polymers as well?
Answer: In this case I would say is more system specific, because we have to add extra coalescence to get the film formation so there are some effects coming from the coalescence agent and not just the binder.
From Dr Tolutope Siyanbola : What is the nature of your hardener in the water based coating system? How did you carryout its optimization in the system.
Answer: In terms of hardener do you meant the thickener or the binder?
From Koray Yıldırı: crosslinker maybe?
From Peter Collins : By hardener I think that the @chi means a 2 pack crosslinker, but I think that these are almost certainly 1 pack air drying coatings that don't have a hardener added.
Answer: Thanks Colin for the explaination…. Yes I didn't use hardener (or cross-linker) and the binder doesn't have cross-linking group
From Joe Keddie : Interesting work. After adding the coalescing aid, what is your VOC content?
Answer: we didn’t calculate because the VOC content in decorative paint it doesn’t count adding a high boiling point coalescence agent, but I would say is around 10% weight.
From Ayse Ersoy : Hi, What is the thickness of the coating? Transparent? Could it be applied to glass?
Answer: we did applied it to glass, but for this we applied it to polypropylene and to aluminium.
From Lee Farren : What film thicknesses have you done your corrosion testing at?
From Ayse Ersoy : what is the thickness please?
Answer: The dry film thickness of the coating is 50 microns.
From Jordan Petkov : Have you evaluated the wetability of the steel by the aqueous solutions of the surfactants?
From Jordan Petkov : Some surfactants subject of size, charge etc. can bring about depletion interaction that can destabilise the dispersion. Have you looked at this?
Answer : I didn't look at the wettability of the surfactant on steel, one of the problem we had with studying the surfactant solution on steel is that flash rusting can occur.
From Jordan Petkov : The wetability should be measured in the framework of seconds, this is relevant to what type of film you form in the first place. The hydrophobic surfactants clearly doesn't help wetability and it was manifested by bad corrosion.
Answer : Jordan, thanks for the interesting comment and I will have a look at the wettability later.....the hydrophobic surfactant is often used as wetting agent for waterborne coating but not specific for steel substrate.